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+The Project Gutenberg EBook of Gas and Oil Engines, Simply Explained, by 
+Walter C. Runciman
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+
+Title: Gas and Oil Engines, Simply Explained
+       An Elementary Instruction Book for Amateurs and Engine Attendants
+
+Author: Walter C. Runciman
+
+Release Date: November 17, 2008 [EBook #27286]
+
+Language: English
+
+Character set encoding: ISO-8859-1
+
+*** START OF THIS PROJECT GUTENBERG EBOOK GAS AND OIL ENGINES ***
+
+
+
+
+Produced by Steven Gibbs, Greg Bergquist and the Online
+Distributed Proofreading Team at https://www.pgdp.net
+
+
+
+
+
+
+
+
+
+
+
+  GAS AND OIL ENGINES
+
+  SIMPLY EXPLAINED
+
+  _An Elementary Instruction Book for Amateurs
+  and Engine Attendants_
+
+
+  BY
+  WALTER C. RUNCIMAN
+
+
+  _FULLY ILLUSTRATED_
+
+
+  LONDON
+
+  Model Engineer Series. The "Model Engineer"
+  Series, no. 26.
+
+  1905
+
+
+
+
+CONTENTS
+
+  CHAP.                                                PAGE
+
+        PREFACE                                           5
+
+
+     I. INTRODUCTORY                                      7
+
+    II. THE COMPONENT PARTS OF AN ENGINE                 13
+
+   III. HOW A GAS ENGINE WORKS                           22
+
+    IV. IGNITION DEVICES                                 33
+
+     V. MAGNETO IGNITION                                 47
+
+    VI. GOVERNING                                        51
+
+   VII. CAMS AND VALVE SETTINGS                          63
+
+  VIII. OIL ENGINES                                      81
+
+
+
+
+PREFACE
+
+
+My object in placing this handbook before the reader is to provide him
+with a simple and straightforward explanation of how and why a gas
+engine, or an oil engine, works. The main features and peculiarities in
+the construction of these engines are described, while the methods and
+precautions necessary to arrive at desirable results are detailed as
+fully as the limited space permits. I have aimed at supplying just that
+information which my experience shows is most needed by the user and by
+the amateur builder of small power engines. In place of giving a mere
+list of common engine troubles and their remedies, I have thought it
+better to endeavour to explain thoroughly the fundamental principles and
+essentials of good running, so that should any difficulty arise, the
+engine attendant will be able to reason out for himself the cause of the
+trouble, and will thus know the proper remedy to apply. This will give
+him a command over his engine which should render him equal to any
+emergency.
+
+  WALTER C. RUNCIMAN.
+
+  LONDON, E.C.
+
+
+
+
+GAS AND OIL ENGINES
+
+SIMPLY EXPLAINED
+
+
+
+
+CHAPTER I
+
+INTRODUCTORY
+
+
+The history of the gas engine goes back a long way, and the history of
+the internal combustion engine proper further still. It will be
+interesting to recount the main points in the history of the development
+of the class of engine we shall deal with in the following pages, in
+order to show what huge strides were made soon after the correct and
+most workable theory had been formulated.
+
+In 1678 Abbé Hautefeuille explained how a machine could be constructed
+to work with gunpowder as fuel. His arrangement was to explode the
+gunpowder in a closed vessel provided with valves, and cool the products
+of combustion, and so cause a partial vacuum to be formed. By the aid of
+such a machine, water could be raised. This inventor, however, does not
+seem to have carried out any experiments.
+
+In 1685 Huyghens designed another powder machine; and Papin, in 1688,
+described a similar machine, which was provided with regular valves, as
+devised by himself, in the _Proceedings of the Leipsic Academy_, 1688.
+From this time until 1791, when John Barber took out a patent for the
+production of force by the combustion of hydrocarbon in air, practically
+no advancement was made. The latter patent, curiously enough, comprised
+a very primitive form of rotary engine. Barber proposed to turn coal,
+oil, or other combustible stuff into gas by means of external firing,
+and then to mix the gases so produced with air in a vessel called the
+exploder. This mixture was then ignited as it issued from the vessel,
+and the ensuing flash caused a paddle-wheel to rotate. Mention is also
+made that it was an object to inject a little water into the exploder,
+in order to strengthen the force of the flash.
+
+Robert Street's patent of 1794 mentions a piston engine, in the cylinder
+of which, coal tar, spirit, or turpentine was vaporised, the gases being
+ignited by a light burning outside the cylinder. The piston in this
+engine was thrown upwards, this in turn forcing a pump piston down which
+did work in raising water. This was the first real gas engine, though it
+was crude and very imperfectly arranged.
+
+In 1801 Franzose Lebon described a machine to be driven by means of
+coal-gas. Two pumps were used to compress air and gas, and the mixture
+was fired, as recommended by the inventor, by an electric spark, and
+drove a piston in a double-working cylinder.
+
+The atmospheric engine of Samuel Brown, 1823, had a piston working in a
+cylinder into which gas was introduced, and the latter, being ignited,
+expanded the air in cylinder whilst burning like a flame. The fly-wheel
+carried the piston up to the top of its stroke, then water was used to
+cool the burnt gases, which also escaped through valves, the latter
+closing when the piston had reached the top of its stroke. A partial
+vacuum was formed, and the atmospheric pressure did work on the piston
+on its down stroke. A number of cylinders were required in this engine,
+three being shown in the specification all connected to the same
+crank-shaft. According to the _Mechanic's Magazine_, such an engine with
+a complete gas generating plant was fitted to a boat which ran as an
+experiment upon the Thames.
+
+A two-cylinder engine working on to a beam was built in Paris, but no
+useful results were obtained.
+
+Wright's engine of 1833 used a mixture of combustible gas and air, which
+operated like steam in a steam engine. This engine had a water-jacket,
+centrifugal governor, and flame ignition. In 1838 Barnett applied the
+principle of compression to a single-acting engine. He also employed a
+gas and air pump, which were placed respectively on either side of the
+engine cylinder, communication being established between the receiver
+into which the pumps delivered and the working cylinder as the charge
+was fired. The double-acting engines which Barnett devised later were
+not so successful.
+
+From this time to about 1860 very few practical developments are
+recorded. A number of French and English patents were taken out,
+referring to hydrogen motors, but are not of much practical value.
+
+Lenoir's patent, dating from 24th January 1860, refers to a form of
+engine which received considerable commercial support, and consequently
+became very popular. A manufacturer, named Marinoni, built several of
+these engines, which were set to work in Paris in a short time. Then,
+due to sudden demand, the Lenoir Company was formed to undertake the
+manufacture of these engines. It was claimed that a 4-horse-power engine
+could be run at a cost of 3ˇ4 shillings per day, or just one half the
+cost of a steam engine using 9ˇ9 pounds of coal per horse-power per
+hour. Many similar exaggerated accounts of their economy in consumption
+were circulated, and the public, on the strength of these figures,
+bought.
+
+It was understood that 17ˇ6 cubic ft. of gas were required per
+horse-power per hour, but it was found that as much as 105 cubic ft.
+were often consumed. The discrepancy between the stated figures and the
+actual performance of the engine was a disappointment to the using
+public, and, as a result, the Lenoir engine got a bad name.
+
+Hugon, director of the Parisian gas-works, who, together with Reithmann,
+a watchmaker of Münich, hotly contested Lenoir's priority to this
+invention, brought out a modification of this engine. He cooled the
+cylinder by injecting water as well as using a water-jacket, and used
+flame instead of electric ignition. The consumption was now brought down
+to 87ˇ5 cubic ft.
+
+At the second Parisian International Exhibition, 1867, an atmospheric
+engine, invented by Otto & Langen about this time, was shown. In this
+engine a free piston was used in a vertical cylinder, the former being
+thrown up by the force of the explosion. The only work done on the
+up-stroke was that to overcome the weight of the piston and piston rod,
+and the latter being made in the form of a rack, engaged with a toothed
+wheel on the axle as the piston descended, causing the fly-wheel and
+pulley to rotate.
+
+Barsanti and Matteucci were engaged in devising and experimenting with
+an engine very similar to this some years before, but Otto & Langen, no
+doubt, worked quite independently. Barsanti's engine never became a
+commercial article; while Otto & Langen's firm, it is said, held their
+own for ten years, and turned out about 4000 engines. In 1862 the French
+engineer, Beau de Rochas, laid down the necessary conditions which must
+prevail in order to obtain maximum efficiency. His patent says there are
+four conditions for perfectly utilising the force of expansion of gas in
+an engine.
+
+(1) Largest possible cylinder volume contained by a minimum of surface.
+
+(2) The highest possible speed of working.
+
+(3) Maximum expansion.
+
+(4) Maximum pressure at beginning of expansion.
+
+These are the conditions and principles, briefly stated, that combine to
+form the now well-known cycle upon which most gas engines work at the
+present time.
+
+It was not until 1876, fifteen years after these principles had been
+enumerated, that Otto carried them into practical effect when he brought
+out a new type of engine, with compression before ignition, higher
+piston speed, more rapid expansion, and a general reduction of
+dimensions for a given power. Due to this achievement, the cycle above
+referred to has always been termed the "Otto" cycle.
+
+
+
+
+CHAPTER II
+
+THE COMPONENT PARTS OF AN ENGINE
+
+
+Having recounted very briefly the chief points in the development of the
+gas engine from its beginning, we may proceed to deal with matters of
+perhaps more practical interest to those who we are assuming have had
+little or no actual experience in making or working internal combustion
+engines.
+
+The modern gas engine comprises comparatively few parts. Apart from the
+two main castings--the bed and cylinder--a small engine, generally
+speaking, consists of four fundamental members, viz., the valves and
+their operating mechanism, the cams and levers; the ignition device for
+firing the charge; and the governing mechanism for regulating the supply
+and admission of the explosive charge. There are innumerable designs of
+each one of these parts, and no two makes are precisely alike in detail,
+as every maker employs his own method of achieving the same end, namely,
+the production of an engine which comprises maximum efficiency with a
+minimum of wear and tear and attention.
+
+Therefore, before dealing with each of these primary parts in an
+arbitrary manner, and with the cycle of operations in detail, we propose
+to make the reader familiar with the general arrangement and method of
+working which usually obtains in the smaller power engines. In the
+following illustrations these parts are shown. A (fig. 1) is the
+ignition device which carries the ignition tube to fire the charge. H
+and I (fig. 2) are the main valves, and GC (fig. 1.) is the gas-cock.
+The side or cam shaft N (sometimes called the 2 to 1 shaft), the cams
+which move the levers M, the latter in turn operating the valves, and
+causing them to open and close at the proper time, are shown in fig. 11.
+A bracket bolted up to the side of cylinder forms a bearing for one end
+of the side shaft, and also carries a spindle at its lower end on which
+the levers oscillate, transmitting the motion imparted to them by the
+cams to the valves. The main cylinder casting and the bed need no
+description. In some cases the bed is in two portions, though now a
+great many makers are discarding the lower portion altogether, having
+found that it is cheaper, and quite as satisfactory, to use a built-up
+foundation instead, and, if necessary, to cut a trough for the fly-wheel
+to run it. This arrangement, however, only obtains where larger engines
+are concerned. A half-compression handle by which the exhaust cam is
+moved laterally on the side shaft as required is not needed on very
+small engines.
+
+[Illustration: FIG. 1.--General Arrangement of a Gas Engine and
+Accessories.]
+
+Further reference will be made to this in another chapter, and,
+although this is not a necessity on a _small_ engine, it is always
+employed on engines over 2 B.H.P. In fig. 1, HW is the cooling water
+outlet and CW the inlet. A small drain cock is shown at DC, through
+which the water in the cylinder water-jacket may be drawn off when
+required. The pipes leading to the inlet and outlet of this supply are
+connected to the cooling water tank by means of a couple of broad, flat
+nuts and lead washers, one inside and the other outside the tank, the
+latter, when clamped up well, making a perfectly water-tight joint. The
+outlet pipe making an acute angle with the side of tank, the washers
+used there should be wedge-shape in section. It is also desirable to fit
+a stop-cock SC, so that the pipes can be disconnected from the engine
+entirely, or the water-jacket emptied without running the whole of the
+water out of the tank. The exhaust pipe EP is made up of gas-barrel. It
+should lead from the engine to the silencer or exhaust box (if one is
+found to be necessary) as directly as possible, _i.e._, with no more
+bends than are needed, and what there are should not be acute. The
+silencer can be inside or outside the engine-room, whichever is most
+convenient; but both it and the exhaust piping should be kept from all
+direct contact with wood-work, and at the same time in a readily
+accessible position.
+
+Beyond the exhaust-pipe and box and the water-tank, the gas bag GB and
+gas meter (where small powers are concerned, the ordinary house or
+workshop lighting meter may be used without inconvenience) are the only
+other accessories which are included in a small installation.
+
+[Illustration: FIG. 2.--A Section of a Gas Engine.]
+
+Fig. 2 gives a sectional view, showing the cylinder and liner. The
+latter is a very desirable feature in any type of gas engine, but
+especially in the larger sizes; for at any future time, should it be
+found necessary to re-bore the liner, it can be removed with comparative
+ease, and is, moreover, more readily dealt with in the lathe than the
+whole cylinder casting would be.
+
+The liner is virtually a cast-iron tube, with a specially shaped flange
+at either end. At the back end the joint between it and the cylinder
+casting has to be very carefully made. This is a water _and_ explosion
+joint; hence it has not only to prevent water entering the cylinder from
+the water-jacket, but also to be sufficiently strong to withstand the
+pressure generated in the cylinder when the charge is fired. For this
+purpose specially prepared coppered asbestos rings are used, which will
+stand both water and intense heat. Sometimes a copper ring alone is
+employed to make the joint. At the front end the liner is just a good
+fit, and enters the bed easily, and a couple of bolts fitted in
+corresponding lugs on the liner, pass through the back end of cylinder
+casting, so that by tightening up these the joint at back end is made
+secure. A small groove is cut on a flange, and a rubber ring, of about
+1/4-in. sectional diameter, is inserted here when the liner is fitted
+into the cylinder casting. This makes the water-jacket joint at the
+front end.
+
+[Illustration: FIG. 3.]
+
+[Illustration: FIG. 5.]
+
+[Illustration: FIG. 4.]
+
+Lugs are provided on the bed and cylinder castings, and are bored to
+receive steel bolts--three are sufficient, provided the metal in and
+around these lugs is not pinched. In some cases a continuous flange is
+provided on both bed and cylinder, and a number of bolts inserted all
+the way round. This, however, is unnecessary, and has a somewhat clumsy
+appearance. When these bolts are tightened up, the cylinder and liner
+are clamped firmly to the bed; but the liner being free at the open end,
+can expand longitudinally without causing stresses in the cylinder
+casting.
+
+The combustion chamber K is virtually part of the cylinder, and has
+approximately equal to one-fourth the total volume of the cylinder. The
+shape varies somewhat in different makes of engines; in some it is
+rectangular, with all the corners well rounded off; in others it is
+practically a continuation of the cylinder, _i.e._, it is circular in
+cross-section, with the back end more or less spherical; while, again,
+it is made slightly oval in cross-section; but in every case the corners
+should be _well_ curved and rounded off, so that there is no one part
+which is liable to become heated disproportionately with the rest of the
+casting; in fact, in the whole cylinder casting there should be no
+sudden change, but a uniformity in the thickness of the metal employed.
+This point should be carefully remembered, although it applies more
+particularly to those parts of the casting subjected to higher
+temperatures than the rest.
+
+The main bearings are usually of brass or gun-metal, and are adjusted
+for running in the same manner as any steam or other engines would be.
+The "brasses" are in halves, and are held down by the cast-iron caps, as
+shown in fig. 1.
+
+These bearings require extremely little attention, and do not show the
+wear and tear of running nearly so soon as the connecting-rod brasses.
+These, too, are usually of brass or gun-metal; but there are various
+forms of construction employed in connection with the back end or piston
+pin bearings. On very small engines the connecting rod is swollen at the
+back end in the forging, and then machined up and drilled, as shown in
+fig. 3. In this hole the brasses are inserted after being scraped up to
+a good fit on the piston pin.
+
+A flat is cut on one of the brasses, and a set screw is fitted, as
+shown, to prevent any movement of the latter after the final adjustment
+has been made. A lock nut should be used in conjunction with this set
+screw. Another method, and one more generally used on larger engines, is
+shown in fig. 4. In this case the brasses are larger than in the former,
+where they are virtually a split bush; here they have holes drilled in
+them to take the bolts, the latter usually and preferably being turned
+up to the shape shown in fig. 5.
+
+
+
+
+CHAPTER III
+
+HOW A GAS ENGINE WORKS
+
+
+The gas engine of the present day, although from a structural point of
+view is very different to the early engine, or even that of fifteen
+years ago, is, in respect to the principle upon which it works, very
+similar. The greater number of smaller power engines in use in this
+country work on what is known as the Otto or four-cycle principle; and
+it is with this class of engine we propose to deal.
+
+Reference to the various diagrams in the text will help considerably,
+and make it an easy matter for any reader hitherto totally unacquainted
+with such engines to see why and how they work.
+
+Coal-gas consists primarily of five other gases, mixed together in
+certain proportions, these proportions varying slightly in different
+parts of the country:--Hydrogen (H), 50; marsh gas (CH4), 38;
+carbon-monoxide, 4; olefines (C6H4), 4; nitrogen (N), 4.
+
+Gas _alone_ is not explosive; and before any practical use can be made
+of it, a considerable quantity of air has to be added, diluting it down
+to approximately ten parts air to one of pure gas. This mixture is _now_
+highly explosive.
+
+The reader will do well to bear these facts constantly in mind,
+especially when he is repairing, adjusting, or experimenting with a gas
+engine. We wish to emphasise this at the outset, because a consideration
+of these facts will keep cropping up throughout all our dealings with
+the gas engine, and if once a fairly clear conception is obtained of how
+gas will behave under certain and various conditions, half, or even more
+than half, our "troubles" will disappear; the cry that the gas engine
+has "gone wrong" will be heard less often, and users would soon learn
+that the gas engine is in reality as worthy of their confidence as any
+other form of power generator in common use.
+
+But to revert to the explanation of the cycle of operations. The cycle
+is completed in four strokes of the piston, _i.e._, two revolutions of
+the crank shaft.
+
+At the commencement of the first out-stroke (the charging or suction
+stroke) gas and air are admitted to the cylinder through the respective
+valves (fig. 6), and continue to be drawn in by what may be termed the
+sucking action of the piston, until the completion of this stroke (the
+_precise_ position of the closing and opening of the valves will be
+referred to later on). The next stroke (fig. 7) is the compression
+stroke. All the valves are closed whilst the piston moves inwards,
+compressing the gases, until at the end of this stroke, and at the
+instant of maximum compression, the highly explosive charge is fired by
+means of the hot tube or an electric spark, as the case may be. The
+ensuing stroke--the second out-stroke of the cycle--is the result of the
+explosion, the expanding gases driving the piston rapidly before them;
+this, then, is the expansion, or working stroke (fig. 8.)
+
+[Illustration: FIG. 6.--Commencement of first out-stroke suction or
+charging stroke. Gas and air valve about to open.]
+
+[Illustration: FIG. 7.--Compression stroke, during which all valves
+remain closed.]
+
+During the last--the second inward--stroke (fig. 9) the exhaust valve is
+opened, and the returning piston sweeps all the burnt gases (the product
+of combustion) out into the exhaust pipe and so into the atmosphere.
+This completes the cycle, and the piston, crank, and valves are in the
+same relative positions as formerly, and the same series of operations
+is repeated again and again. Of course, it is not always the case that
+both air _and_ gas valve are opened on the charging stroke; that depends
+upon the method employed to govern the speed of the engine. Supposing
+it were governed on the hit and miss principle (to be explained
+hereafter), the gas valve would be allowed to remain closed during the
+charging stroke, and air alone would be drawn into the cylinder, then
+compressed, but not being explosive would simply expand again on the
+working stroke, giving back nearly all the energy which was absorbed in
+compressing it, and finally be exhausted in the same manner as the burnt
+gases are.
+
+[Illustration: FIG. 8.--Second out stroke, showing position of valves
+during working stroke.]
+
+[Illustration: FIG. 9.--Second inward stroke, showing position of valves
+during the exhaust stroke.]
+
+[Illustration: FIG. 10.--First out-stroke, showing position of valves
+during the charging stroke.]
+
+Fig. 10 shows diagrammatically the position of crank, piston, and
+valves _during_ the charging stroke.
+
+[Illustration: FIG. 11.--Cross Section of Cylinder.]
+
+In figs. 1 and 2 we gave drawings of two gas engines, which are typical
+examples of modern practice. Huge strides have been made in recent years
+in gas-engine work, as regards both workmanship and efficiency, so that
+to-day we have in the gas engine a machine whose mechanical efficiency
+compares favourably with that of any other power generator, and whose
+thermal efficiency is very much greater.
+
+[Illustration: FIG. 12.--Longitudinal Section of Cylinder.]
+
+Figs. 11 and 12 show respectively a sectional end and side elevation of
+the cylinder, from which it will not be difficult for the reader,
+however unacquainted he may be with gas-engine work, to see how the
+various requirements and peculiarities of the engine should be
+considered and provided for.
+
+A most important desideratum in any machine or engine is that it shall
+be as simple in construction as ever possible; complicated mechanism
+should only be introduced when such addition or complication compensates
+adequately for what must necessarily be a higher first cost, and
+incidentally the greater wear and tear and attention involved. Figs. 11
+and 12 show what has been done to simplify the construction of the gas
+engine in recent years. The main feature in this case is the very
+get-at-able position of the two main valves--the air valve F and the
+exhaust E. These valves, as may be seen from the drawing, are capable of
+withdrawal after the cover of the combustion chamber has been removed.
+The latter is an iron casting, shaped and faced up to make an absolutely
+tight joint; no asbestos or any packing is used to make this joint--and
+is held in place by four studs, as shown. Thus, all that is necessary is
+to remove the four nuts, lift the cover off, then pull out the pins
+which keep the spiral springs in position, and withdraw the valves. The
+latter are seated direct on to the metal of the cylinder casting, the
+gun-metal bushes A and B acting as guides. Further reference to A (the
+mixer), which serves a twofold purpose, will be made later on.
+
+The gas valve and cock are mounted in a separate casting, which is
+carried by a couple of studs, the joint between this and cylinder being
+made with a piece of rubber insertion. The gas enters at the gas-cock,
+passes through the valve and port G, and round the annular space in the
+bush or "mixer" A, previously mentioned, and thence through a number of
+small holes in same, immediately below the seat of the air valve F. At
+the same time, pure air is drawn in _via_ the air box (as explained
+hereafter), through port L (fig. 11), and thence up the centre of bush A
+and over the small holes through which the gas is flowing. The two then
+thoroughly mix and enter the combustion chamber together as the air
+valve F is opened. This device produces a perfectly homogeneous mixture,
+which conduces in no small measure to perfect combustion when the
+explosion takes place, and upon which, to a very great extent, depends
+the efficiency of the engine. Besides possible loss in this direction,
+however, there is another source of waste which cannot be eliminated,
+and that is the heat taken away by the cooling water which surrounds the
+cylinder. As this loss is inevitable, the best thing we can do is to
+make it as small as possible. Theoretically, it would be no small
+advantage if we could work at very much higher temperatures than we do
+at the present time, and it is only certain mechanical difficulties
+which bar the way and so effectually prevent the already high thermal
+efficiency of the engine being greatly increased.
+
+It is no easy matter to overcome these difficulties completely, but
+improvements in this direction are continually being made, so that
+troubles which attended the gas-engine user years ago no longer exist.
+
+All that we require of the cooling water is that it shall keep certain
+working parts of the engine at a reasonable temperature; for instance,
+the cylinder must not be so hot as to deprive the lubricating oil of its
+property to lubricate, neither must the exhaust valve become so hot as
+to cause it to seize in the bush and stick up; but, beyond such
+considerations as these, the higher the temperature is at the
+commencement of each explosion the more efficient will the engine be.
+The object, then, is to do as little cooling as possible, and to apply
+the cooling effect at the right parts; hence the passages and chambers
+through which the cooling water circulates should be so arranged that
+those which require to be kept at a low temperature are in close
+proximity to the cooling water. On some of the engines of days gone by,
+the exhaust valve was carried in a large iron casting, this in turn
+being bolted to the cylinder casting and communicating with the
+combustion chamber by means of a port. Such an arrangement was found to
+be not only clumsy but inefficient; the water passages were small and
+difficult to get at; they readily furred up; and moreover, the joint
+between this casting and the cylinder was necessarily a water _and_
+explosion joint, and the fewer we have of these the better.
+
+The method--if it may be called a method--of overcoming or preventing
+the exhaust valve becoming too hot is, in the case of figs. 11 and 12,
+simply one of judicious arrangement and design. The cooling water enters
+by the inlet K (fig. 11), and circulates round the exhaust valve port X
+and valve E immediately, before becoming heated, thus keeping the
+hottest of the working parts of the engine at a suitable temperature;
+and the valve seat, being in direct metallic communication with the cold
+water, does not become burnt or pitted. On the other side of the exhaust
+valve we have the air valve and its passages, through which cool air is
+continually being drawn; this also helps to keep the exhaust valve cool.
+
+From this, then, we may conclude that overheating of the cylinder will
+not occur under normal conditions, given an engine of good design; but,
+if this trouble does arise, we may safely look first of all for some
+defect in the cooling water circulation. Some waters contain a greater
+amount of impurities than others, and consequently the water space may
+furr up more rapidly in one district than in another. But this deposit,
+even under the worst conditions, accumulates very slowly, and the
+operation of cleaning out the water-jacket is a very infrequent
+necessity. The exhaust valve, however, may become overheated if it is
+allowed to get into bad condition, _i.e._, leaky. Its seat should be
+well looked after, or the hot gases will blow past when it is
+presumably shut; and if this defect, slight though it may be to begin
+with, is allowed to develop, both the seat, the valve head, and the
+spindle will become burnt away and pitted, perhaps badly, due to the
+excessive heat.
+
+
+
+
+CHAPTER IV
+
+IGNITION DEVICES
+
+
+The ignition devices commonly employed may be divided into three main
+classes--the metal tube, the porcelain tube, and the electric ignition.
+These again may be subdivided: The first being either iron or nickel
+(hecknum as they are sometimes called); the second are of two
+kinds--single-ended and double-ended; and the third takes many forms
+which many of my readers are possibly well acquainted with, such as the
+magneto, the induction coil and trembler, and the high-tension magneto
+ignition, the latter device having been used successfully on various
+occasions, though not yet universally adopted.
+
+The first-named have one or two advantages over the nickel tube. They
+are very inexpensive, and are easily heated to the required temperature;
+moreover, they can be made at home, should occasion demand. On the other
+hand, they are not so durable, have a very uncertain life, and
+consequently need renewing frequently--their average life being not
+more than 60 working hours. Fig. 13 gives an outline drawing of an iron
+tube, with its burner and chimney fixed in position. The tube is very
+similar to a piece of 1/4-in. gas-barrel, closed up at one end and a
+taper thread (1/4-in. gas) cut on the other; in fact, gas-barrel may be
+used for making these tubes at home--and measure about 7 or 8 in. over
+all It is screwed into a firing block, which in turn is screwed into the
+combustion chamber end, so that when right home it is in such position
+that the tube stands quite vertical. The section of the tube, fig. 13,
+shows the condition it gets into after having been in use some time. The
+bore, it will be seen, has become almost completely closed up, so that
+there is practically no communication between the hot part of the tube
+and the combustion chamber. This closing up of the bore is very gradual,
+and it is in the early stages of this process that erratic firing is
+likely to occur; sometimes the charge will be successfully fired and
+sometimes not. It may be as well to mention here that the length of the
+tube, although to a certain extent immaterial, should neither be
+excessively long nor abnormally short, the precise length varying with
+the size of the engine. A 1/4-in. tube, 8 ins. long, may be used
+successfully on engines ranging from 1/2 to 6 horse-power, provided a
+suitable burner is fitted enabling the tube to be heated at any required
+spot. After the first charge has been fired, and the exhaust takes
+place, practically all the burnt gases are cleared out of the cylinder,
+but a small amount of these will generally remain in the tube and the
+bore of the firing block. On the ensuing compression stroke these inert
+gases are compressed to the far end of the tube, thus making way for the
+explosive mixture to reach the hot portion, and explode, thus sending a
+jet of flame into the main volume of the mixture which is immediately
+ignited. Hence there is no advantage in having a tube too long, while,
+on the other hand, it _must_ not be too short.
+
+[Illustration: FIG. 13.]
+
+[Illustration: FIG. 14.]
+
+[Illustration: FIG. 15.]
+
+The asbestos lining, shown in fig. 13, may be of various thicknesses,
+according to the size of the chimney and the tube; the reason for this
+will be apparent to many; but being a most important factor in the
+heating of the tube, and consequently the working of the engine, it will
+be advisable to deal with this point more fully.
+
+Due mainly to the peculiar behaviour of iron tubes under heat and
+internal pressure, it is always advisable to look to them first of all
+when the engine shows signs of missing fire; and to always examine the
+bore of a fresh one, and ascertain that it is perfectly clear before
+putting it in. The adjustment of the ignition tube, although one of the
+most important and necessary to be made on the whole engine, is in
+itself a perfectly simple matter. It must be understood that the
+ignition tube cannot, with the ordinary means at our disposal, be kept
+at too high a temperature; but it must not be assumed that either the
+_size_ of the flame, or the _time_ the flame has been alight, is
+conclusive evidence that the tube is, or ought to be, sufficiently hot
+to fire the charge successfully. It is an uncommon thing to hear a man
+exclaim--after it has been pointed out that his tube is practically
+cold--"Why, it's been alight for hours!"
+
+If such is the case with you, reader, you may very rightly assume that
+the burner is not properly adjusted, and so does not give the _right
+kind of flame_.
+
+In order to get the hottest possible flame, the quantity of gas and air
+must be mixed in the right proportions. A common fault is that there is
+too much gas allowed to flow through the nipple, compared with the
+amount of air being drawn in at the air aperture, fig. 13. The result
+is, we get a flame of great length, but one which is not at all suited
+to our requirements; and instead of giving up its heat to the tube and
+the asbestos lining of the chimney, a large amount of gas we are
+presumably burning _in_ the chimney is not being burnt there at all,
+for, on applying a light just above the chimney top, a quantity of this
+gas we are wasting will be seen to burn with a flickering blue flame.
+
+To put matters right, it is necessary to do one of two things--either
+cut down the supply of gas or increase the air-supply. Providing the air
+aperture is normal, _i.e._, the same size as it was originally, it is
+better to adjust the _gas_, which may be done by tapping up the nipple
+N, as indicated in the enlarged sketch, fig. 14, until just the right
+amount of gas can flow.
+
+As a rule, if there is too much air, the flame will burn with a loud
+roaring noise, and is liable to fire back. The nipple should then be
+opened out with a small reamer--the tang of a small file, ground to a
+long taper point, makes an admirable tool for this purpose. Whether the
+burner is of the ordinary bunsen type, or the ring or stove type, the
+above remarks apply, as in every case the flow of gas is governed by the
+size of the orifice through which it flows.
+
+There is no need to use anything beyond a touch of oil when putting in a
+new tube, in order to make a perfectly tight joint; white or red lead
+are quite unnecessary, and are liable to make it a troublesome matter to
+remove the tube on future occasions. Neither should undue force be
+applied when putting in new tubes; it is liable to wear the thread in
+the firing block, which results in a partial stoppage of the ignition
+hole, as indicated in fig. 15. This is especially the case if we happen
+to get hold of a tube with its screwed part slightly smaller than usual.
+
+The asbestos with which the chimney is lined should be about 1/8 in.
+thick, and, when renewing, the same thickness should be used as
+originally. A thicker board will reduce the annular space round the
+tube, and will have a choking effect on the flame--much the same as
+referred to above, when there is too much gas and not enough air. A
+simple method of lining the chimney is to cut a block of wood to the
+inside dimensions of the chimney, less 1/4 in. in width and thickness,
+then soften the asbestos cardboard by immersing in water, and bend it
+round the wood, cutting off to the required size, _i.e._, till the two
+edges form a neat butt joint. It can be allowed to remain on the mould
+until dry--when it will retain its shape--or can be put into the chimney
+straight away, if it is wanted for use immediately. In the latter case,
+however, it will be some fifteen minutes or so before the tube will
+attain its working temperature. Asbestos linings gradually become worn
+and ragged, and small flakes are apt to detach themselves and fall down
+into the burner, which, of course, prevents the flame playing as it
+should around the tube. In such cases it is not always necessary to fit
+a new lining; if the chimney is removed, the loose flakes shaken out and
+the asbestos well damped and patted down with a wooden or steel
+foot-rule or other suitably shaped tool, it will be fit for another long
+spell of work.
+
+The nickel or hecknum tubes are treated in the same manner as the iron,
+but, as we mentioned before, are more durable, but require more heating
+to get them up to a workable temperature. Their greater first cost is
+compensated to some extent by makers in some cases guaranteeing them for
+six months.
+
+Of the porcelain ignition devices, we will deal with the double-ended
+tube first, it being the more commonly used of the two in this country.
+This form of tube is usually about 3 in. long, 1/2 in. diameter, and
+open at both ends. It may be mounted in a metal casting, in form not
+unlike the small gas stoves for heating soldering irons. It is heated
+the greater part of its length by a couple of rows of gas jets, and is
+frequently surrounded by an asbestos lining. The whole arrangement is
+in reality a tiny furnace. When in position for working, one end of the
+tube is open to the ignition passage leading and communicating with the
+combustion chamber, while the other end is sealed, through butting up
+against a metal cap or plate. An asbestos washer is interposed between
+the tube at each end and the metal it bears against, thus making a more
+or less flexible joint. A thumb screw is arranged at the outside end of
+the tube, by means of which pressure can be applied to clamp it up
+between the washers to the desired extent. Some care has to be exercised
+in adjusting this form of tube for running. When heated to the working
+temperature it, of course, expands, so that, if tightened up too much
+when cold, it is under a fairly high compression; and when the engine is
+started, and the explosion takes place, it not infrequently bursts, if
+there is not sufficient "give" in the washers to allow for the
+expansion. On the other hand, if not clamped up sufficiently tight to
+start with, when the explosion occurs, the washer at one or each end is
+blown out. This adjustment has to be made to a nicety, and, although a
+somewhat difficult matter, success may be attained after one or two
+trials. It is advisable, after a new tube has been put in, to start up
+the engine gently, _i.e._, with less than the normal supply of gas, and
+increase to the full amount gradually whilst running. This may be done
+by simply opening the gas-cock on engine partially in the first place.
+
+The single-ended porcelain tube is not so well known here as on the
+continent; why, we cannot say; certainly it is preferable in every way.
+We give a few illustrations, showing the method of using this tube.
+
+Figs. 16 and 17 show the general arrangement of tube and chimney and the
+manner in which they are fixed to the cylinder. The device consists
+primarily of three parts--the body or chimney B, the cover C, and the
+tube itself T. The body is a light iron casting, carried by a couple of
+studs SS, which are either screwed into the firing block F, or direct
+into the metal of the cylinder casting if no firing-block is used; the
+latter may very well be dispensed with in the smaller-sized engines.
+
+The tube is made of thin porcelain, slightly bell-mouthed at its open
+end, and is mounted in a thick metal washer W, as shown in fig. 18 in
+section, the joint being made with a little asbestos paper, moistened.
+
+The block F and the face of the body B (fig. 16) are recessed to take
+the washer W easily, but the depth of both recesses taken together must
+be about 1/16 in. less than the thickness of the washer W; thus, when
+the tube is placed in position between the body B and the block F, and
+the former screwed up by means of the two nuts, as shown in the figure
+16, the effect is to clamp the _washer_ which carries the tube, but _not
+the porcelain tube itself_.
+
+[Illustration: FIG. 16.]
+
+[Illustration: FIG. 17.]
+
+[Illustration: FIG. 18.]
+
+The latter is left perfectly free to expand; and yet, owing to its
+particular shape, the pressure in the cylinder during the compression
+and explosion stroke only tends to make the joint between the tube and
+washer more secure. The action of this ignition device depends upon the
+tube heater H, which is merely a small bunsen burner, the flame of which
+impinges on the tube at one particular spot, raising it to a very high
+temperature--almost white heat. Most of my readers will know the
+formation of the bunsen flame. It in composed of two distinct zones. The
+inner one, marked A in fig. 18, is a perfectly cold part of the flame,
+and appears to be a pale-blue coloured cone.
+
+It is the outer zone which is the hot portion of the flame, hence this
+part _only_ must be allowed to play on the tube. The tip of the blue
+cone A must be kept about 1/4 in. below the tube, in order to ensure the
+hottest part of the flame impinging precisely where the heat is
+required.
+
+The total length of the whole flame is, to a certain extent, immaterial;
+but, generally speaking, it should be adjusted so that the length of the
+inner cone A is about 1 in. or 1-1/4 in. The same methods which we
+described in the early part of this chapter can be employed in the
+adjustment of this burner, but some care should be exercised to get the
+correct flame length.
+
+The result of allowing the cold part of the flame to impinge on the tube
+is observable in fig. 18. The black spot indicated on the drawing
+actually appears as a black or sooty spot when looking at the tube under
+these conditions; but in reality no discoloration whatever takes place,
+the spot disappearing immediately the cone A is made shorter, or the
+burner H lowered in the chimney B, so that the tip of A is just below,
+and does not touch the tube at all.
+
+The adjustment of the length of cone A may be accomplished in two
+ways--(1) by keeping the supply of gas constant, and varying the amount
+of air admitted at aperture K, fig. 18; (2) by keeping the supply of air
+constant, and varying the amount of gas admitted through nipple N. The
+first method is to be preferred when it is necessary to make any slight
+adjustment due to the variation of gas pressure during the day, and may
+be accomplished by fitting a small sliding shield G, as shown in the
+figs. 16 and 17, and moving it round so that it covers, more or less,
+the aperture K. Thus the length of cone A may be adjusted to a nicety in
+a very few seconds. This shield keeps all draughts and puffs of wind
+from the fly-wheel away from the aperture, and helps the flame to burn
+very steadily. In the first place, of course, the flame will be
+regulated by opening out or tapping up the nipple N (an enlarged sketch
+of which is given in fig. 14), so that cone A is just about 1-1/4 in.
+long when air aperture is full open; but once this is done, any future
+adjustment can be made by throttling the air-supply, or raising or
+lowering the burner bodily, the set screw keeping it in any desired
+position (see fig. 17).
+
+From the foregoing remarks it will be seen that the most noteworthy
+features of this form of ignition are the ease and certainty with which
+the tube can be fixed in a few moments; that when the two nuts on the
+studs SS have been tightened up there is no likelihood of the joints
+being "blown," for, as we said before, only the metal washer is clamped
+up, the porcelain tube itself being as free to expand as it was before.
+It is also at once obvious when any adjustment of the flame is
+necessary; there need be no uncertainty as to whether the tube is hot
+enough or not.
+
+
+
+
+CHAPTER V
+
+MAGNETO IGNITION
+
+
+The third form of ignition we have to deal with is the electric.
+
+There are a great number of different types made and used, but for
+gas-engine use perhaps that known as the magneto ignition is the most
+satisfactory. With this form, neither accumulators, dry batteries, or
+spark coils are required, and consequently a greater simplicity is
+arrived at than would otherwise be the case.
+
+In fig. 19 we show diagrammatically the ordinary form of magneto
+machine. Virtually it is a small dynamo which is fixed to the side of
+cylinder casting, and is operated in the manner shortly to be described.
+As we do not propose to enter into more than a brief explanation of why
+and how this apparatus generates current to produce the required spark,
+perhaps a simple analogy will make matters most intelligible to any
+reader not well acquainted with electrical phenomena. We know that when
+a current of electricity is flowing in a wire, and the wire be suddenly
+broken, a spark will occur at the point of breakage. This fact may be
+observed in an ordinary electric bell when ringing; at the tip of the
+contact breaker a number of tiny sparks may be seen to occur, due to the
+rapid make and break of the current flowing in the circuit. Precisely
+the same action takes place in our magneto-igniter, but, instead of a
+multitude of tiny sparks, we produce one at a time, at definite
+intervals, viz., at the commencement of each explosion stroke.
+
+[Illustration: FIG. 19.]
+
+In the later form of magneto machines there is a soft iron sleeve
+between the magnet poles and the armature. The former is connected to a
+system of levers by which a reciprocating motion is imparted to it by
+means of a suitably arranged cam on the side shaft. It has been found
+that better results are obtained by causing the magnetic field to move
+relative to the armature winding than to move the latter through a
+stationary field. Reference to the diagrams, figs. 20 and 21, will make
+this clear.
+
+In fig. 19 the cam C is shown just on the point of allowing the lever L
+to fly back into its normal position, due to the action of the springs
+comprising a dashpot S. As the cam rotates, it pushes the lever L to the
+left, the sleeve (or virtually the armature A) is also rotated through a
+portion of a revolution comparatively slowly; but as soon as L is
+released, the sleeve (or armature) flies back again almost
+instantaneously and for the moment is generating a current in the same
+manner as would any ordinary continuous current dynamo.
+
+[Illustration: FIG. 20.]
+
+[Illustration: FIG. 21.]
+
+At the instant the maximum current is being generated, the circuit is
+broken by means of the contact breaker D, fig. 19, which we show in
+detail in fig. 22. The latter is mounted on the end of the combustion
+chamber, and consists of two parts, D and P.
+
+[Illustration: FIG. 22.]
+
+D is an easy fit in the hole bored to receive it, and has a mushroom
+valve head and seating, as shown, so that it moves readily when struck
+by the projection E on the rod R (fig. 19); but yet, acting in the
+manner of a non-return valve, it allows no gas to escape when the
+explosion takes place in the cylinder. D is therefore in direct metallic
+communication with the engine frame and earth.
+
+P is a fixed metal pin, carefully insulated from all contact with the
+engine frame and earth. To this pin one end of the armature winding is
+connected, whilst the other end is connected to the engine frame.
+
+Thus a closed circuit is formed, and when the current is generated it
+flows from one terminal of magneto through wire to pin P, on to D,
+through D to earth (_i.e._, engine frame), and so back to other terminal
+on magneto.
+
+And as the circuit is broken between D and P, we obtain a spark, as
+previously explained, which may be timed to take place by adjusting the
+position of cam C on side shaft relatively to the position of piston.
+
+It may be said that the position of the magneto-igniter is immaterial;
+it will be fixed in different positions on different types of engines,
+and so long as the operating mechanism is simple and effective, _i.e._,
+as direct as is practicable, it works well, and requires little
+attention. The timing of the spark will be dealt with in the chapter on
+Cams and Valve Settings.
+
+
+
+
+CHAPTER VI
+
+GOVERNING
+
+
+The devices for governing the speed of the engine may be divided,
+broadly speaking, into two classes--the inertia or hit and miss
+governor, and the centrifugal. Of the latter type we will give an
+instance first. In figs. 23 and 24 the governor gear is shown
+diagrammatically, consisting of a couple of weights WW suspended from a
+vertical spindle. These fly apart when caused to revolve by the bevel
+wheel gearing BB, and raise the sleeve S to a greater or lesser extent.
+A recess in the latter engages a lever arm L, through which the vertical
+movement of the sleeve S is converted into a horizontal movement of the
+sleeve T. The latter is carried by the valve lever P, and is virtually a
+roller which engages with one or other of the steps of the cam C,
+according to the speed of the engine. The object of this arrangement is
+to keep the ratio of air to gas uniform throughout all variations of
+load. The gas and air valve are shown as both being operated by the same
+lever P, the accurate timing of the latter being obtained by means of
+set screws.
+
+[Illustration: FIG. 23.]
+
+[Illustration: FIG. 24.]
+
+Messrs Dougill & Co.'s engines are fitted with a step down cam and
+governor such as this. The centrifugal governor is often arranged so
+that instead of the charge being merely reduced in volume, the whole
+charge is cut out, and no explosion whatever takes place. (In this
+respect the same results are obtained as when a hit and miss governor is
+used, and the latter form therefore is to be preferred, especially on
+small engines, where the difference between the indicated power and the
+brake power is always, even under the best conditions, fairly great.)
+
+In this case the governor lever only operates the gas valve; the air
+valve being opened on every charging or suction stroke, whether gas is
+admitted or not.
+
+Another application of the centrifugal governor is to suspend a distance
+piece on the end of the governor lever, so that at normal speed this
+distance piece is interposed between the gas valve spindle and the lever
+operating it. In that case the gas valve will be opened. But if the
+speed is above the normal, the distance piece will be raised clear of
+the valve spindle, and the opening mechanism (driven by a cam on the
+side shaft) will simply move forward and recede again without ever
+touching the gas valve.
+
+There are any number of movements which have been, and there are many
+more which could be, devised to give the same result; and it depends
+principally upon the form of engine in question which device we adopt.
+
+The simplest and most direct action is, however, always the best;
+complicated mechanism is to be deprecated, especially on small engines.
+For this reason is the inertia governor more generally fitted to such
+engines.
+
+[Illustration: FIG. 25.]
+
+A simple form of this governor is shown in fig. 25. The gas valve V is
+shown on its seating. It is screwed into a pecker block B, and pinned as
+shown. The latter should be of cast steel, tempered to a straw colour;
+or if mild steel or iron is used, it must be well case-hardened, in
+order to resist wear. The pecker P (also tempered hard) is mounted on
+the cast-iron weight W, which in turn is pivoted on the valve lever L.
+It will be seen that the weight W (which is only held in the position
+shown by the spring S) will tend to lag behind when a sudden upward
+motion is imparted to the lever L. Thus it depends upon the degree of
+suddenness with which L moves whether the pecker P remains in the same
+relative position to the lever as the latter travels upwards and engages
+with the pecker block B, or whether it misses it and simply slides over
+the face of the block. The adjustment of the spring S is effected by
+screwing up or slacking out the milled nuts T; and on the degree to
+which this spring is compressed depends the sensitiveness of the
+governor, and consequently the speed of the engine. To obtain accurate
+and steady governing with this type of mechanism it is essential that
+the weight be perfectly free on its spindle, and that nothing but the
+spring S holds, or tends to hold, it in the position shown. On this
+account it is advisable to provide a "lip" on the pecker block, as
+shown, to keep the area of contact as small as possible. This
+effectually prevents any sticking, should a superfluity of oil happen to
+get on either block or pecker. For similar reasons there should be some
+clearance between A and the pecker, _i.e._, the latter should only bear
+at one point and not bed flat against A.
+
+Another form of inertia governor is shown in fig. 26 of the hit and miss
+type, which is employed by Messrs Capel & Co. on many of their engines.
+
+It consists of three main parts--the brass arm L carried on a stud D, on
+which it is free to move; the weight W, which carries the pecker P
+pivoted at the upper end of L; and the pecker block B, which engages the
+pecker when the engine requires a charge of gas.
+
+The governing action is dependent upon the shape of the operating cam
+from X to Y. (In the case already dealt with, the lever L serves to
+operate both air and gas valves, and so one cam only is necessary; but
+in this instance the gas valve is operated by a separate cam, and a
+greater nicety of adjustment is obtainable.)
+
+[Illustration: FIG. 26.]
+
+If the speed of the engine is sufficiently high, the arm L is thrust
+forward at such a rate that the weight W tends to lag behind, with the
+result that P is raised above the notch in B, as shown by the dotted
+lines in drawing. On the other hand, when the speed is too low, the arm
+L will not be thrust forward with so great a degree of suddenness, the
+weight W will have time to move with L, and the relative position of W
+and P to L will remain the same. Hence, in the first case, when a
+_further_ forward movement is given to L by the cam, the pecker P is
+clear of B, and omits to open the gas valve V; in the second case, P
+engages with B, and the gas valve is held open during the time the
+portion of cam Y to Z is passing over the roller R on arm L.
+
+The great drawback to some forms of governors is not that they fail to
+govern well when new, but that no provision is made to ensure them
+working steadily when a bit worn. The shape of the cam has everything to
+do with the regular working of this form of governor.
+
+Supposing our cam was of the shape shown in fig. 27, _i.e._, the
+governing and opening portion all in one curve, it would cause the
+pecker to move both _forward_ and in an _upward_ direction at the _same
+time_, so that at the moment of engaging B, P might still be moving in
+an upward direction, which would cause uncertainty of action, especially
+if the tips of the engaging members were at all blunt through wear; and,
+in all probability, P would fly off B after partially opening the gas
+valve.
+
+This behaviour is very undesirable, as the small quantity of gas so
+admitted to the cylinder is quite useless, and a sheer waste is
+incurred. With the governing arrangement shown in fig. 26, this trouble
+does not exist. The cam is so designed that the first rise from X to A
+determines whether or not the valve is to be opened; the curve from A to
+Y is struck from the centre of the side shaft; thus, during that
+portion of the revolution the arm L is stationary, and the pecker at the
+same instant takes up a definite position either in the notch in B or on
+top of it, and is ready to open the valve if the speed of the engine is
+such as to require an explosion, or simply to slide over the top of B,
+allowing the valve to remain closed. It is most interesting to observe
+the action of this governor; when an engine fitted with one is running
+very slowly, the three distinct movements of the pecker P may be clearly
+discerned as the respective portions of the cam pass over the small
+roller R.
+
+[Illustration: FIG. 27.]
+
+
+
+
+CHAPTER VII
+
+CAMS AND VALVE SETTINGS
+
+
+With the gas, as with any other kind of engine, the valve settings are
+of primary importance. On very small engines it is often the case that
+only the exhaust valve is operated mechanically.
+
+Again, there are several well-known makes which operate the gas and
+exhaust mechanically while the air valve is opened by suction alone.
+Though opinions differ as to which is the best course to take, there can
+be little doubt that, with all three valves mechanically operated, a
+greater nicety of adjustment is obtainable than would be otherwise
+possible. And provided the working parts are neatly made and finished,
+they will take but little power to drive them; and such loss would be
+compensated by the additional power and efficiency obtained from the
+engine, due to satisfactory and correct adjustment.
+
+In fig. 28 we give a diagram showing the exact positions of the crank
+when the gas, air, and exhaust valves open and close respectively, under
+normal conditions of working. The solid circle represents the first
+revolution of the crank shaft, starting from the commencement of the
+suction stroke, and the dotted circle the second revolution, during
+which the explosion and exhaust strokes take place; the dotted
+horizontal line shows the position of crank at the back and front dead
+centres.
+
+As a clear conception of why certain things happen under certain
+conditions is most desirable, we will first describe the operation of
+marking off the cams which operate the respective valve levers, and then
+discuss the effect of various "settings" of the valves on the running of
+the engine.
+
+[Illustration: FIG. 28.]
+
+Assuming that we are still dealing with the Otto cycle engine, the cam
+or side shaft will revolve at precisely half the speed of the crank
+shaft. This 2 to 1 motion is obtained by means of toothed wheels, or a
+screw gear. In the former case, where plain or bevel cog-wheels are
+employed, the one fixed on the crank shaft must be exactly half the
+diameter of the one on the side shaft, _i.e._, it must have one half the
+number of teeth. On the other hand, if a screw gear is used, the
+relative diameters of the two wheels may vary, but the pitch of the
+teeth on the one must be twice that of the other. These wheels sometimes
+have the teeth or thread formed in the casting, and sometimes they are
+cut after a plain casting has been made. The latter kind are, needless
+to say, better than the former, which often require filing up in order
+to make every tooth alike, and ensure sweet running.
+
+We know already in what positions our crank has to be at the opening and
+closing of the three valves, and with the aid of the diagram, fig. 28,
+we can determine the size of the cams. In fig. 29, S is the side shaft
+to which the cams have to be keyed, R the roller on valve lever, the
+latter being represented by the centre lines LL, as all we require to
+find is the motion this lever will transmit to the valve, the spindle of
+which is shown at V.
+
+Fig. 30 shows diagrammatically the position of crank at the opening and
+closing of the air valve. From this we see that the angle through which
+the crank travels during the time the air valve is open is equal to the
+obtuse angle ABC. Now, as the side shaft S revolves at half the speed of
+crank, it is obvious that the former will travel through only half that
+angle in the same space of time, _i.e._, through an angle equal to ABD.
+We can now transfer this angle on to S, fig. 29, and draw two lines SE,
+SF, cutting a circle GHJ, representing the back of the cam, which latter
+passes in front of the roller R without causing any movement of the
+lever L.
+
+[Illustration: FIG. 29.]
+
+[Illustration: FIG. 30.]
+
+[Illustration: FIG. 31.]
+
+It will be seen that by drawing a line forming a tangent to the circle
+GHJ at F and another at E, and producing these, they will meet at point
+K. Consequently, as the side shaft rotates in the direction indicated,
+the lever L will _begin_ to open the valve V when the cam is in the
+position shown in fig. 29, reach a maximum opening at K, and finally
+close when the cam has moved so that point E is now where F was. With a
+cam of this shape, however, a considerable portion of the stroke would
+have passed before the valve was raised any _appreciable_ distance off
+its seat; it would only be fully open for an instant, viz., when K was
+passing over R, and would begin to close again directly.
+
+Moreover, if the engine were running at even a slow speed, the motion
+imparted to lever L would be indefinite; and this, especially if the
+governor is fitted to the air valve lever, as in fig. 25, is very
+undesirable. Therefore, to obtain a definite opening we must set out the
+cam, as shown in fig. 31. In this diagram the roller is shown standing
+clear of the back of cam by about 1/16 in. A line MN is then drawn,
+forming a tangent to both roller R and circle GHJ at points F and O
+respectively. This gives us the opening portion of cam. Then from the
+centre S with radius SF describe the arc FE (shown dotted in fig. 31),
+and set off the angle required (ABD, fig. 30), as previously explained.
+Through point E draw a line forming a tangent to circle GHJ, and produce
+it towards P. This line gives us the closing portion of cam. The
+distance W is of course variable, according to the amount of lift we
+give the valve. By comparing these two diagrams it will be seen that in
+both cases the valve will be opened the same length of time, but in
+first case the motion will be indefinite and uncertain. In practice the
+corners are rounded off somewhat, in order to obtain a steady motion;
+and when the air cam is also the governing cam, it is advisable to round
+off the opening face, as indicated in fig. 32. Upon the shape of this
+face both the sensitiveness and the life of the governor gear depends.
+If it is nicely rounded off, giving a gradual rise, very little tension
+(or compression, as the case may be) of the controlling spring will be
+necessary to give the required speed to engine; whereas, if the rise is
+sudden, the spring will have to be screwed up tighter, and, if uneven
+and lumpy (_i.e._, not a fair curve), the result will, of course, be
+erratic governing.
+
+[Illustration: FIG. 32.]
+
+A certain amount of clearance should always be provided between the
+roller and the back of cam (compare figs. 29 and 31), that is, the
+roller should not bear against the cam, except during that portion of
+the stroke in which it is actually operating the valve, viz., from F to
+E (fig. 31). A small stop interposed between the lever and some
+convenient part of the engine, such as the side-shaft bracket bearing,
+answers this purpose.
+
+[Illustration: FIG. 33.]
+
+[Illustration: FIG. 34.]
+
+The size and shape of the exhaust cam is found in the same manner as
+above described; the angle through which it operates is greater than
+that of the air cam, and is shown in fig. 33. A fair margin should be
+allowed for filing or machining these castings up; the shape and sizes
+arrived at by the above described method being finished measurements.
+Fig. 34 gives the outline of an exhaust cam worked out from the setting
+diagram, fig. 33.
+
+[Illustration: FIG. 35.]
+
+[Illustration: FIG. 37.]
+
+[Illustration: FIG. 41.]
+
+[Illustration: FIG. 42.]
+
+We may now consider the relative positions these two cams will occupy
+when keyed up on the side shaft. Assuming that we have both cams
+finished to the proper shape and size, and the keyway cut in the side
+shaft, we can commence to mark off the position of keyway in the air
+cam. With the crank in the position shown in fig. 35, the air cam is
+slipped on to the side shaft and brought to the position shown in fig.
+32. The keyway being already cut in the side shaft, the position for
+that in the cam may be scribed off, as shown by dotted lines (fig. 32),
+the cam removed, and the keyway cut. It is as well, however, to check
+this mark by turning the crank round to position shown in fig. 37,
+_i.e._, the closing of air valve. The side shaft will also turn through
+exactly half this angle, so that when the cam is again slipped on the
+latter, the scriber marks and keyway in shaft should be exactly in line,
+as they were in fig. 32, and the fall of the cam--the closing
+portion--should just be touching roller R, but not sufficient to keep
+the valve open (see fig. 38). The slightest movement of the crank from
+this point in a forward direction should result in a little play being
+felt in the lever L, assuming that the cam is also moved just enough to
+keep the scriber marks in line with the existing keyway.
+
+[Illustration: FIG. 36.]
+
+[Illustration: FIG. 38.]
+
+[Illustration: FIG. 39.]
+
+By these operations it will be at once evident whether the cam is too
+large or too small. Supposing it is too small, we will obtain two sets
+of marks indicating the position of keyway, as shown in fig. 39, and it
+is obvious that we must give the lever less play by screwing up the set
+screws shown in fig. 11. The effect of this is to cause the valve to
+open earlier and close later than it would if the play were greater; as
+it would were the operating portion of cam larger. A minimum amount of
+play must always be allowed, however. When two sets of marks are
+obtained, the mean must be taken and the keyway cut as shown by the
+thick lines in fig. 39. The exhaust cam in larger engines is usually
+made with a swelling on the opening portion, as shown in fig. 40, so
+that the valve is _very slightly_ opened some time before the crank has
+reached the position shown in fig. 41. Fig. 42 shows position of crank
+at the close of exhaust valve, and the two last-mentioned diagrams
+correspond with the two positions in which the exhaust cam is shown in
+fig. 34. The small lump on the back of exhaust cam, fig. 40, is only
+required on engines above 3 B.H.P. to relieve the compression on the
+compression stroke when starting up. By moving the roller R on valve
+lever longitudinally, so that it engages both parts of cam as they pass
+in front of it, the exhaust valve is held open during a small portion of
+the compression stroke, usually closing when the crank has reached the
+bottom centre.
+
+Referring again to fig. 26, this gas or governor cam may be set out, and
+the keyway marked on the same principle as already described for the air
+and exhaust valves. An end view of the three cams keyed up on the side
+shaft is given in fig. 40A. In small engines it is convenient to have
+the air and exhaust cams made in one casting, when one key only will be
+required. On some engines, instead of employing a movable roller or
+valve lever, the exhaust cam is fitted on side shaft with a
+"feather"--_i.e._, a headless key--and the cam being capable of
+longitudinal movement, such movement being controlled by a small lever
+or handle, called the half-compression lever.
+
+[Illustration: FIG. 40.]
+
+[Illustration: FIG. 40A.]
+
+Having once thoroughly grasped the important part the cams play in the
+working of the engine, it will be an easy matter to adjust the valve
+settings, and to keep them adjusted correctly. The effect of a wrong
+setting will then be strikingly apparent. On small engines a separate
+cam to operate the gas valve is not a necessity; and the practice of
+fitting the gas valve spindle (or the pecker, the effect would be the
+same) with a device for increasing or diminishing its length, is also
+unnecessary and unsound.
+
+The wear on a well-designed gas valve operating mechanism is practically
+nil; and even if there was wear, the effect would be to cause the valve
+to open a trifle later and close sooner than it would otherwise, _i.e._,
+it would remain open a shorter time during each charging stroke. This in
+turn (other conditions remaining the same) would give us a weaker
+mixture; and although too weak a mixture is preferable to a too rich
+one, we should have to adopt some means of increasing the richness of
+the mixture; otherwise the maximum power of the engine would soon be
+seen to diminish.
+
+To get the mixture normal again we must either enlarge the gas inlet or
+cut down the air-supply somewhat, and so keep the proportions the same.
+That is to say, the quality of the mixture is dependent upon the
+relative dimension of the gas and air inlets. We know by actual trial
+that if at the completion of the charging stroke the pressure in the
+cylinder is approximately that of the atmosphere, better results are
+obtained than when the pressure is considerably below that of the
+atmosphere. Thus, the larger we make the inlet ports (but still
+retaining correct relative dimensions) the more readily will the mixture
+be drawn into the cylinder as the piston moves forward, tending to
+create a vacuum. Of the two courses open to us to retain a good mixture
+it is preferable to open out the gas-supply, for by cutting down the
+air-supply, and sucking the gas in, due to the partial vacuum being
+formed, we should be keeping the proportions correct at the expense of
+reducing the total volume of the explosive mixture (more strictly
+speaking, the density of the charge) admitted to the cylinder.
+
+Under normal conditions it is not necessary to create a high vacuum to
+suck the gas into the cylinder, but it is as well to understand what
+results we would tend to produce, did we work on these lines. Of course,
+with small high-speed engines fitted with suction air valve, the vacuum
+is higher than it would be in slow-speed engines with mechanically
+operated valves. If we take an extreme case as an example, where, to get
+any gas to speak of into the cylinder the air-supply would have to be
+cut down or throttled to an abnormal extent, we will realise at once
+that such a small quantity of both air and gas would have been drawn in,
+and consequently the mixture would be so rarefied that on the
+compression stroke the pressure would possibly be extremely low and
+totally inadequate to produce efficient working. Moreover, working at
+such a high vacuum as this would not only prevent us obtaining a normal
+explosion in the cylinder, but would upset the working of the exhaust
+valve. The latter being held down on its seat during the suction stroke
+by means of a spiral spring would be lifted off its seat by suction (the
+partial vacuum in the cylinder), and any burnt gases which happened to
+be hanging about in the exhaust port or pipe would be drawn into the
+cylinder again, and tend to damp the ensuing explosion. Too early
+closing of the exhaust should be avoided almost as rigorously as too
+late. The latter will affect the working in a similar way to the exhaust
+being lifted on the charging stroke by suction; on the other hand, if it
+closes too soon, the entire volume of burnt gases will not have been
+swept out of the cylinder, and the effect will again be to damp the
+following explosion.
+
+The gas valve opens just after the crank is above the back centre and
+closes just before the front centre is reached, that is, opening a
+little after the air valve and closing a shade before it, thus every
+particle of gas is used in the cylinder, due to a draught of air being
+drawn in after the gas valve has been closed.
+
+The settings of the valve being of primary importance, no matter what
+size engine we are dealing with, and being also the most confusing
+matter for anyone unacquainted with gas engines to grasp, it will not be
+out of place to suggest a simple method of checking these settings.
+
+Let us begin by pulling the fly-wheel round backwards until we feel the
+piston is on the compression stroke, then from this point--the crank
+being about 45° above the front centre--pull the wheel round until the
+crank is in the position for the exhaust opening (see fig. 28). In this
+position there should be but the _slightest_ play in the exhaust lever,
+showing that the valve is _just_ on point of opening; and by keeping
+one's hand on the lever whilst the fly-wheel is pulled round _very
+slowly_ (it is a good plan to get some one else to do the pulling
+round), it is possible to ascertain the precise point at which the valve
+opens. Next pull round till the crank is in the position for the air
+valve opening, and observe that it is set correctly. Then go on to a
+trifle above the back centre, where the exhaust valve should close, and
+so on till the opening and closing of each valve has been checked. It
+will be noticed that the air, and sometimes the gas, valve opens before
+the exhaust closes. This overlap is necessary; and it will be found that
+the smaller the engine and the higher the speed the greater this overlap
+will be to obtain good results, although a good deal of individual
+judgment must be used in settling the exact amount of overlap, as the
+requisite amount may, to get the best results, vary in different engines
+of precisely the same dimensions and type.
+
+When dealing with engines which have no separate gas valve--the gas
+being admitted with the air, which is sometimes the case with very small
+engines--the above notes referring to the gas setting independently,
+will, of course, not hold good.
+
+It may be mentioned with regard to the lump on the opening side of the
+exhaust cam, that this if overdone is found to be detrimental on large
+engines, and even on small ones. If it is too large, it will cause both
+exhaust valve and seat to become burnt and pitted, due to the surface
+being exposed to the exceedingly high temperature of the expanding
+gases. If it is too large, it is equivalent to opening the exhaust valve
+too early, and the effect is the same, viz., a waste of power and damage
+to the valve and its seat.
+
+[Illustration: FIG. 43.]
+
+[Illustration: FIG. 44.--Brake Testing.]
+
+The method of grinding in the valves to their seats with emery powder
+and oil is so well known that no further description is needed here. We
+give, however, in fig. 43 a sketch showing a very expeditious way of
+dealing with very badly worn or burnt seats. The sketch explains itself.
+Such a tool is readily made; even the cutter could be turned and filed
+up to shape and then hardened at home. By lightly tapping in the taper
+cotter pin little by little, sufficient pressure is put on the cutter to
+make it an easy matter to completely re-face an old seat or form a new
+one. A T-wrench or "tommy" can be used to work the cutter spindle. The
+lower part of the latter must be the same diameter as the existing valve
+spindle; the bush acts as a guide; and as the bevel of the cutter
+should be the same as that of the valve, a very little grinding in with
+emery powder is required to finish the job off.
+
+In fig. 44 we give a diagram showing the method of testing for Brake
+H.P. of engine, as it is frequently interesting to make such a simple
+test after any alterations or adjustments have been made.
+
+Two spring balances and a rope or cord (according to the size of the
+engine), fitted with a few wood blocks as shown in section, fig. 44, to
+keep the rope on the rim of fly-wheel, is all that is required for this
+test. The following formula may be used for arriving at the B.H.P.:--
+
+  B.H.P. = (S1 - S2) 3.14 x D x R / 33000
+
+  S1 = Reading in lbs. of spring balance No. 1.
+  S2 = Reading in lbs. of spring balance No. 2.
+  D =  Diameter of fly-wheel and diameter of brake
+       rope in feet.
+  R =  Revolutions of fly-wheel per minute.
+
+  As 3.14 x D / 33000 will always remain the same for any given engine and
+  gear, we may call that expression C; then the B.H.P. may be written--
+
+  B.H.P. = (S1 - S2) C R
+
+
+
+
+CHAPTER VIII
+
+OIL ENGINES
+
+
+The small oil engine is practically the same as the gas engine, with the
+addition of a vaporiser for converting the oil into gas, or vapour, to
+be exploded in the cylinder; consequently the one may be converted into
+the other in many cases without much trouble. The difficulty of
+producing an efficient oil engine lies principally in devising a
+satisfactory and reliable vapouriser--one which will work equally well
+under all loads. The heat supplied to the chamber must be sufficient to
+vaporise the oil, but not great enough to decompose it. There are
+various methods of vaporising the oil, and many types of vaporisers are
+employed to attain the same end. There are some in which a charge of oil
+is drawn by suction into a hot chamber in which it is converted into
+vapour and at the same time mixed with a small quantity of hot air; this
+rich mixture is then passed into the combustion chamber of the engine,
+in the same manner as coal-gas would be, where it is further diluted
+with more air drawn in through the air valve. Other arrangements cause
+a jet of oil to be injected into a chamber containing hot air, in the
+form of spray, which immediately converts the oil into vapour, and is
+then passed into the cylinder, compressed, and fired. Then, again, we
+can pump oil through a spraying nipple into the vapouriser (which is
+kept at a suitable temperature) whilst the cylinder is being filled with
+air on the suction stroke. On the following compression stroke the air
+is driven into the vapouriser, which communicates with the cylinder
+through a narrow neck, and mixes intimately with the oil vapour.
+Gradually, as the pressure rises, due to compression, the charge becomes
+more and more explosive, until at the completion of this stroke it has
+attained the proper proportions of air and oil vapour, and is fired by
+the temperature of the vapouriser and that caused by a high compression;
+that is, the charge is fired automatically; and once the engine is
+running, no heating lamp is required to keep the vapouriser at the
+correct temperature. It is necessary, however, to raise it to the
+workable temperature at starting. This is known as the Hornsby-Akroyd
+method.
+
+Capel's arrangement is also simple and efficient, and has the additional
+advantage of being capable of being fitted to their existing gas
+engines, the conversion being made in a very short time. This vapouriser
+consists primarily of a tubular casting A, on the outside of which are
+formed a series of vertical ribs, shown in plan, fig. 46, running to
+within a short distance of the flange at one end, as shown in the
+section, fig. 45, thus providing an annular space C between the upper
+ends of the ribs and the flange. This casting is enclosed by an outer
+casing B, which fits well over the inner tube. It has also a number of
+small holes drilled near the lower end communicating with the channels
+between the ribs. Thus it will be seen that when the gas valve is opened
+and suction takes place, air is drawn in through these holes, passes up
+into the annular space C below the top flange, from there travels to the
+opposite side of vapouriser, and mixes with the oil which is also being
+drawn in through a small nipper at N, fig. 45. Both then pass between a
+series of pegs, where they become thoroughly mixed, and finally pass on
+to the inlet valve V, fig. 47, and so into the cylinder, where the
+complete charge is mixed up and compressed and fired in the usual
+manner. Iron ignition tubes may be used, and one heating lamp serves a
+double purpose in keeping the tube and vapouriser hot at the same time.
+This lamp is fed by means of a pump actuated from the side shaft. The
+plunger of the pump is loaded with a spiral spring, which may be
+adjusted to give any desired pressure, and is kept constant and steady
+by means of an air vessel. This pump is shown in fig. 48. It is actuated
+by means of a rod and lever from the side shaft of engine. The plunger P
+works in a barrel B, which is carried by a small reservoir R, the latter
+being in communication with the main oil tank by means of the pipe H.
+
+[Illustration: FIG. 46.]
+
+[Illustration: FIG. 45.]
+
+[Illustration: FIG. 47.]
+
+[Illustration: FIG. 48.]
+
+[Illustration: FIG. 49.]
+
+[Illustration: FIG. 50.]
+
+[Illustration: FIG. 51.]
+
+The plunger is loaded with a spiral spring, and has a ball valve, as
+shown. Intermediate between this small reservoir and the main oil tank
+is another set of valves, shown in fig. 49. It will be seen that the
+suction of the pump will draw the oil up, the small and lower ball
+valve, of course, allowing it to pass freely. On the down stroke the
+lower valve will be automatically closed, and the oil will be put under
+pressure, this being determined by the load on the plunger valve, which
+is adjustable by means of the screw S, fig. 48. When the required
+pressure in the pipe P, figs. 45 and 49, has been attained, the plunger
+valve lifts on each stroke and the surplus oil flows through the plunger
+into the small reservoir R. The latter is at about the same level as
+another still smaller reservoir M (shown in figs. 47 and 50), a flow of
+oil being established between the two by means of a pipe Q (see figs. 48
+and 50). In the reservoir R is fitted an overflow pipe, so that the oil
+cannot rise beyond a certain level; hence the head of oil in the smaller
+one M is always constant. On the suction stroke a partial vacuum is
+formed in the engine cylinder, consequently the pressure in the
+vapouriser drops somewhat below that of the atmosphere, and this small
+difference in pressure is enough to cause the oil to rise in the small
+passage X, fig. 45, beyond its normal level, and overflow into the
+vapourising chamber, as previously described. The valve or nipper N is
+shown open in the diagram, fig. 45, and all that is required to stop the
+engine when running is to drop the small handle L, fig. 45, when the
+valve will close, due to the spring S. The air vessel shown in fig. 49
+is in communication with the pipe leading to the blow lamp. A pressure
+gauge can also be fitted, although it is not in any way a necessity.
+
+The ratchet wheel and pawl shown in fig. 48 are part of the lubricator.
+The wheel drives a brass or gun-metal plug, producing an intermittent
+rotary motion. The plug has a small hole in its periphery, which becomes
+filled with oil when it is at the upper part of its travel, and empties
+the oil out into a discharge pipe T, when it is inverted, and is then
+led away and applied to the piston at the required spot. Fig. 51 shows
+this arrangement in section.
+
+
+
+
+
+End of the Project Gutenberg EBook of Gas and Oil Engines, Simply Explained, by 
+Walter C. Runciman
+
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+<html xmlns="http://www.w3.org/1999/xhtml">
+  <head>
+    <meta http-equiv="Content-Type" content="text/html;charset=iso-8859-1" />
+    <title>
+      The Project Gutenberg eBook of Gas and Oil Engines Simply Explained,
+      by Walter C. Runciman.
+    </title>
+    <style type="text/css">
+/*<![CDATA[  XML blockout */
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+
+<pre>
+
+The Project Gutenberg EBook of Gas and Oil Engines, Simply Explained, by 
+Walter C. Runciman
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+
+Title: Gas and Oil Engines, Simply Explained
+       An Elementary Instruction Book for Amateurs and Engine Attendants
+
+Author: Walter C. Runciman
+
+Release Date: November 17, 2008 [EBook #27286]
+
+Language: English
+
+Character set encoding: ISO-8859-1
+
+*** START OF THIS PROJECT GUTENBERG EBOOK GAS AND OIL ENGINES ***
+
+
+
+
+Produced by Steven Gibbs, Greg Bergquist and the Online
+Distributed Proofreading Team at https://www.pgdp.net
+
+
+
+
+
+
+</pre>
+
+
+
+
+
+
+
+<h1>Gas and Oil Engines<br />
+
+<small>SIMPLY EXPLAINED</small></h1>
+
+<p class="center"><i>An Elementary Instruction Book for Amateurs<br />
+and Engine Attendants</i><br /><br /><br /></p>
+
+
+<p class="center"><small>BY</small><br />
+WALTER C. RUNCIMAN<br />
+<br />
+<br />
+<i>FULLY ILLUSTRATED</i><br /><br /><br /><br /><br /><br /></p>
+
+
+<p class="t1">LONDON<br /><br />
+
+Model Engineer Series. The "Model Engineer"<br />
+Series, no. 26.<br /><br />
+
+1905</p>
+
+
+
+<hr  />
+<h2>CONTENTS</h2>
+
+
+
+
+
+<div class='center'>
+<table border="0" width="50%" cellpadding="4" cellspacing="0" summary="Contents">
+<tr>
+ <td align='right'><small>CHAP.</small></td>
+ <td>&nbsp;</td>
+ <td align='right'><small>PAGE</small></td></tr>
+<tr>
+ <td>&nbsp;</td>
+ <td align='left'>PREFACE</td>
+ <td align='right'><a href="#PREFACE">5</a></td></tr>
+<tr>
+ <td align='right'>I.</td>
+ <td align='left'>INTRODUCTORY</td>
+ <td align='right'><a href="#CHAPTER_I">7</a></td>
+</tr>
+<tr>
+ <td align='right'>II.</td>
+ <td align='left'>THE COMPONENT PARTS OF AN ENGINE</td>
+ <td align='right'><a href="#CHAPTER_II">13</a></td>
+</tr>
+<tr>
+ <td align='right'>III.</td>
+ <td align='left'>HOW A GAS ENGINE WORKS</td>
+ <td align='right'><a href="#CHAPTER_III">22</a></td>
+</tr>
+<tr>
+ <td align='right'>IV.</td>
+ <td align='left'>IGNITION DEVICES</td>
+ <td align='right'><a href="#CHAPTER_IV">33</a></td>
+</tr>
+<tr>
+ <td align='right'>V.</td>
+ <td align='left'>MAGNETO IGNITION</td>
+ <td align='right'><a href="#CHAPTER_V">47</a></td>
+</tr>
+<tr>
+ <td align='right'>VI.</td>
+ <td align='left'>GOVERNING</td>
+ <td align='right'><a href="#CHAPTER_VI">51</a></td>
+</tr>
+<tr>
+ <td align='right'>VII.</td>
+ <td align='left'>CAMS AND VALVE SETTINGS</td>
+ <td align='right'><a href="#CHAPTER_VII">63</a></td>
+</tr>
+<tr>
+ <td align='right'>VIII.</td>
+ <td align='left'>OIL ENGINES</td>
+ <td align='right'><a href="#CHAPTER_VIII">81</a></td>
+</tr>
+</table></div>
+
+
+
+<hr /><p><span class='pagenum'><a name="Page_5" id="Page_5">[Pg 5]</a></span></p>
+<h2><a name="PREFACE" id="PREFACE"></a>PREFACE</h2>
+
+
+<p class="noin"><span class="smcap">My</span> object in placing this handbook before the reader is to provide him
+with a simple and straightforward explanation of how and why a gas
+engine, or an oil engine, works. The main features and peculiarities in
+the construction of these engines are described, while the methods and
+precautions necessary to arrive at desirable results are detailed as
+fully as the limited space permits. I have aimed at supplying just that
+information which my experience shows is most needed by the user and by
+the amateur builder of small power engines. In place of giving a mere
+list of common engine troubles and their remedies, I have thought it
+better to endeavour to explain thoroughly the fundamental principles and
+essentials of good running, so that should any difficulty arise, the
+engine attendant will be able to reason out for himself the cause of the
+trouble, and will thus know the proper remedy to apply. This will give
+him a command over his engine which should render him equal to any
+emergency.</p>
+
+<p class="right">
+WALTER C. RUNCIMAN.<br />
+</p>
+<p><span class="smcap">London, E.C.</span><br />
+<span class='pagenum'><a name="Page_6" id="Page_6">[Pg 6]</a></span></p>
+
+
+
+<hr /><p><span class='pagenum'><a name="Page_7" id="Page_7">[Pg 7]</a></span></p>
+<h1>GAS AND OIL ENGINES<br />
+
+<small>SIMPLY EXPLAINED</small></h1>
+
+
+
+<hr style="width: 15%;" />
+<h2><a name="CHAPTER_I" id="CHAPTER_I"></a>CHAPTER I</h2>
+
+<h3>INTRODUCTORY</h3>
+
+
+<p class="noin"><span class="smcap">The</span> history of the gas engine goes back a long way, and the history of
+the internal combustion engine proper further still. It will be
+interesting to recount the main points in the history of the development
+of the class of engine we shall deal with in the following pages, in
+order to show what huge strides were made soon after the correct and
+most workable theory had been formulated.</p>
+
+<p>In 1678 Abb&eacute; Hautefeuille explained how a machine could be constructed
+to work with gunpowder as fuel. His arrangement was to explode the
+gunpowder in a closed vessel provided with valves, and cool the products
+of combustion, and so cause a partial vacuum to be formed. By the aid of
+such a machine, water could be raised. This inventor, however, does not
+seem to have carried out any experiments.</p>
+
+<p><span class='pagenum'><a name="Page_8" id="Page_8">[Pg 8]</a></span></p><p>In 1685 Huyghens designed another powder machine; and Papin, in 1688,
+described a similar machine, which was provided with regular valves, as
+devised by himself, in the <i>Proceedings of the Leipsic Academy</i>, 1688.
+From this time until 1791, when John Barber took out a patent for the
+production of force by the combustion of hydrocarbon in air, practically
+no advancement was made. The latter patent, curiously enough, comprised
+a very primitive form of rotary engine. Barber proposed to turn coal,
+oil, or other combustible stuff into gas by means of external firing,
+and then to mix the gases so produced with air in a vessel called the
+exploder. This mixture was then ignited as it issued from the vessel,
+and the ensuing flash caused a paddle-wheel to rotate. Mention is also
+made that it was an object to inject a little water into the exploder,
+in order to strengthen the force of the flash.</p>
+
+<p>Robert Street's patent of 1794 mentions a piston engine, in the cylinder
+of which, coal tar, spirit, or turpentine was vaporised, the gases being
+ignited by a light burning outside the cylinder. The piston in this
+engine was thrown upwards, this in turn forcing a pump piston down which
+did work in raising water. This was the first real gas engine, though it
+was crude and very imperfectly arranged.</p>
+
+<p>In 1801 Franzose Lebon described a machine to be driven by means of
+coal-gas. Two pumps were used to compress air and gas, and the mixture
+was fired, as recommended by the inventor, by an electric spark, and
+drove a piston in a double-working cylinder.</p>
+
+<p><span class='pagenum'><a name="Page_9" id="Page_9">[Pg 9]</a></span></p><p>The atmospheric engine of Samuel Brown, 1823, had a piston working in a
+cylinder into which gas was introduced, and the latter, being ignited,
+expanded the air in cylinder whilst burning like a flame. The fly-wheel
+carried the piston up to the top of its stroke, then water was used to
+cool the burnt gases, which also escaped through valves, the latter
+closing when the piston had reached the top of its stroke. A partial
+vacuum was formed, and the atmospheric pressure did work on the piston
+on its down stroke. A number of cylinders were required in this engine,
+three being shown in the specification all connected to the same
+crank-shaft. According to the <i>Mechanic's Magazine</i>, such an engine with
+a complete gas generating plant was fitted to a boat which ran as an
+experiment upon the Thames.</p>
+
+<p>A two-cylinder engine working on to a beam was built in Paris, but no
+useful results were obtained.</p>
+
+<p>Wright's engine of 1833 used a mixture of combustible gas and air, which
+operated like steam in a steam engine. This engine had a water-jacket,
+centrifugal governor, and flame ignition. In 1838 Barnett applied the
+principle of compression to a single-acting engine. He also employed a
+gas and air pump, which were placed respectively on either side of the
+engine cylinder, communication being established between the receiver
+into which the pumps delivered and the working cylinder as the charge
+was fired. The double-acting engines which Barnett devised later were
+not so successful.</p>
+
+<p>From this time to about 1860 very few practical<span class='pagenum'><a name="Page_10" id="Page_10">[Pg 10]</a></span> developments are
+recorded. A number of French and English patents were taken out,
+referring to hydrogen motors, but are not of much practical value.</p>
+
+<p>Lenoir's patent, dating from 24th January 1860, refers to a form of
+engine which received considerable commercial support, and consequently
+became very popular. A manufacturer, named Marinoni, built several of
+these engines, which were set to work in Paris in a short time. Then,
+due to sudden demand, the Lenoir Company was formed to undertake the
+manufacture of these engines. It was claimed that a 4-horse-power engine
+could be run at a cost of 3&middot;4 shillings per day, or just one half the
+cost of a steam engine using 9&middot;9 pounds of coal per horse-power per
+hour. Many similar exaggerated accounts of their economy in consumption
+were circulated, and the public, on the strength of these figures,
+bought.</p>
+
+<p>It was understood that 17&middot;6 cubic ft. of gas were required per
+horse-power per hour, but it was found that as much as 105 cubic ft.
+were often consumed. The discrepancy between the stated figures and the
+actual performance of the engine was a disappointment to the using
+public, and, as a result, the Lenoir engine got a bad name.</p>
+
+<p>Hugon, director of the Parisian gas-works, who, together with Reithmann,
+a watchmaker of M&uuml;nich, hotly contested Lenoir's priority to this
+invention, brought out a modification of this engine. He cooled the
+cylinder by injecting water as well as using<span class='pagenum'><a name="Page_11" id="Page_11">[Pg 11]</a></span> a water-jacket, and used
+flame instead of electric ignition. The consumption was now brought down
+to 87&middot;5 cubic ft.</p>
+
+<p>At the second Parisian International Exhibition, 1867, an atmospheric
+engine, invented by Otto &amp; Langen about this time, was shown. In this
+engine a free piston was used in a vertical cylinder, the former being
+thrown up by the force of the explosion. The only work done on the
+up-stroke was that to overcome the weight of the piston and piston rod,
+and the latter being made in the form of a rack, engaged with a toothed
+wheel on the axle as the piston descended, causing the fly-wheel and
+pulley to rotate.</p>
+
+<p>Barsanti and Matteucci were engaged in devising and experimenting with
+an engine very similar to this some years before, but Otto &amp; Langen, no
+doubt, worked quite independently. Barsanti's engine never became a
+commercial article; while Otto &amp; Langen's firm, it is said, held their
+own for ten years, and turned out about 4000 engines. In 1862 the French
+engineer, Beau de Rochas, laid down the necessary conditions which must
+prevail in order to obtain maximum efficiency. His patent says there are
+four conditions for perfectly utilising the force of expansion of gas in
+an engine.</p>
+
+<p>(1) Largest possible cylinder volume contained by a minimum of surface.</p>
+
+<p>(2) The highest possible speed of working.</p>
+
+<p>(3) Maximum expansion.</p>
+
+<p><span class='pagenum'><a name="Page_12" id="Page_12">[Pg 12]</a></span></p><p>(4) Maximum pressure at beginning of expansion.</p>
+
+<p>These are the conditions and principles, briefly stated, that combine to
+form the now well-known cycle upon which most gas engines work at the
+present time.</p>
+
+<p>It was not until 1876, fifteen years after these principles had been
+enumerated, that Otto carried them into practical effect when he brought
+out a new type of engine, with compression before ignition, higher
+piston speed, more rapid expansion, and a general reduction of
+dimensions for a given power. Due to this achievement, the cycle above
+referred to has always been termed the "Otto" cycle.</p>
+
+
+
+<hr /><p><span class='pagenum'><a name="Page_13" id="Page_13">[Pg 13]</a></span></p>
+<h2><a name="CHAPTER_II" id="CHAPTER_II"></a>CHAPTER II</h2>
+
+<h3>THE COMPONENT PARTS OF AN ENGINE</h3>
+
+
+<p>Having recounted very briefly the chief points in the development of the
+gas engine from its beginning, we may proceed to deal with matters of
+perhaps more practical interest to those who we are assuming have had
+little or no actual experience in making or working internal combustion
+engines.</p>
+
+<p>The modern gas engine comprises comparatively few parts. Apart from the
+two main castings&mdash;the bed and cylinder&mdash;a small engine, generally
+speaking, consists of four fundamental members, viz., the valves and
+their operating mechanism, the cams and levers; the ignition device for
+firing the charge; and the governing mechanism for regulating the supply
+and admission of the explosive charge. There are innumerable designs of
+each one of these parts, and no two makes are precisely alike in detail,
+as every maker employs his own method of achieving the same end, namely,
+the production of an engine which comprises maximum efficiency with a
+minimum of wear and tear and attention.</p>
+
+<p><span class='pagenum'><a name="Page_14" id="Page_14">[Pg 14]</a></span></p><p>Therefore, before dealing with each of these primary parts in an
+arbitrary manner, and with the cycle of operations in detail, we propose
+to make the reader familiar with the general arrangement and method of
+working which usually obtains in the smaller power engines. In the
+following illustrations these parts are shown. A (fig. 1) is the
+ignition device which carries the ignition tube to fire the charge. H
+and I (fig. 2) are the main valves, and GC (fig. 1.) is the gas-cock.
+The side or cam shaft N (sometimes called the 2 to 1 shaft), the cams
+which move the levers M, the latter in turn operating the valves, and
+causing them to open and close at the proper time, are shown in fig. 11.
+A bracket bolted up to the side of cylinder forms a bearing for one end
+of the side shaft, and also carries a spindle at its lower end on which
+the levers oscillate, transmitting the motion imparted to them by the
+cams to the valves. The main cylinder casting and the bed need no
+description. In some cases the bed is in two portions, though now a
+great many makers are discarding the lower portion altogether, having
+found that it is cheaper, and quite as satisfactory, to use a built-up
+foundation instead, and, if necessary, to cut a trough for the fly-wheel
+to run it. This arrangement, however, only obtains where larger engines
+are concerned. A half-compression handle by which the exhaust cam is
+moved laterally on the side shaft as required is not needed on very
+small engines.</p>
+
+<p><span class='pagenum'><a name="Page_15" id="Page_15">[Pg 15]</a></span></p>
+
+<div class="figcenter" style="width: 500px;">
+<img src="images/image1.jpg" width="500" height="325" alt="Fig. 1." title="" />
+<span class="caption"><span class="smcap">Fig. 1.</span>&mdash;General Arrangement of a Gas Engine and
+Accessories.</span>
+</div>
+
+<p><span class='pagenum'><a name="Page_16" id="Page_16">[Pg 16]</a></span></p><p>Further reference will be made to this in another chapter, and,
+although this is not a necessity on a <i>small</i> engine, it is always
+employed on engines over 2 B.H.P. In fig. 1, HW is the cooling water
+outlet and CW the inlet. A small drain cock is shown at DC, through
+which the water in the cylinder water-jacket may be drawn off when
+required. The pipes leading to the inlet and outlet of this supply are
+connected to the cooling water tank by means of a couple of broad, flat
+nuts and lead washers, one inside and the other outside the tank, the
+latter, when clamped up well, making a perfectly water-tight joint. The
+outlet pipe making an acute angle with the side of tank, the washers
+used there should be wedge-shape in section. It is also desirable to fit
+a stop-cock SC, so that the pipes can be disconnected from the engine
+entirely, or the water-jacket emptied without running the whole of the
+water out of the tank. The exhaust pipe EP is made up of gas-barrel. It
+should lead from the engine to the silencer or exhaust box (if one is
+found to be necessary) as directly as possible, <i>i.e.</i>, with no more
+bends than are needed, and what there are should not be acute. The
+silencer can be inside or outside the engine-room, whichever is most
+convenient; but both it and the exhaust piping should be kept from all
+direct contact with wood-work, and at the same time in a readily
+accessible position.</p>
+
+<p>Beyond the exhaust-pipe and box and the water-tank, the gas bag GB and
+gas meter (where small powers are concerned, the ordinary house or
+workshop lighting meter may be used without inconvenience) are the only
+other accessories which are included in a small installation.</p>
+
+<p><span class='pagenum'><a name="Page_17" id="Page_17">[Pg 17]</a></span></p>
+<div class="figcenter" style="width: 500px;">
+<img src="images/image2.jpg" width="500" height="318" alt="Fig. 2." title="" />
+<span class="caption"><span class="smcap">Fig. 2.</span>&mdash;A Section of a Gas Engine.</span>
+</div>
+
+<p><span class='pagenum'><a name="Page_18" id="Page_18">[Pg 18]</a></span></p><p>Fig. 2 gives a sectional view, showing the cylinder and liner. The
+latter is a very desirable feature in any type of gas engine, but
+especially in the larger sizes; for at any future time, should it be
+found necessary to re-bore the liner, it can be removed with comparative
+ease, and is, moreover, more readily dealt with in the lathe than the
+whole cylinder casting would be.</p>
+
+<p>The liner is virtually a cast-iron tube, with a specially shaped flange
+at either end. At the back end the joint between it and the cylinder
+casting has to be very carefully made. This is a water <i>and</i> explosion
+joint; hence it has not only to prevent water entering the cylinder from
+the water-jacket, but also to be sufficiently strong to withstand the
+pressure generated in the cylinder when the charge is fired. For this
+purpose specially prepared coppered asbestos rings are used, which will
+stand both water and intense heat. Sometimes a copper ring alone is
+employed to make the joint. At the front end the liner is just a good
+fit, and enters the bed easily, and a couple of bolts fitted in
+corresponding lugs on the liner, pass through the back end of cylinder
+casting, so that by tightening up these the joint at back end is made
+secure. A small groove is cut on a flange, and a rubber ring, of about
+<span class="above">1</span>&#8260;<span class="below">4</span>-in. sectional diameter, is inserted here when the liner is fitted
+into the cylinder casting. This makes the water-jacket joint at the
+front end.</p>
+
+<p><span class='pagenum'><a name="Page_19" id="Page_19">[Pg 19]</a></span></p>
+<div class="figcenter" style="width: 450px;">
+<img src="images/image3.jpg" width="450" height="137" alt="Fig. 3." title="" />
+<span class="caption"><span class="smcap">Fig. 3.</span></span>
+</div>
+
+<div class="figcenter" style="width: 350px;">
+<img src="images/image5.jpg" width="350" height="71" alt="Fig. 5." title="" />
+<span class="caption"><span class="smcap">Fig. 5.</span></span>
+</div>
+
+<div class="figcenter" style="width: 450px;">
+<img src="images/image4.jpg" width="450" height="137" alt="Fig. 4." title="" />
+<span class="caption"><span class="smcap">Fig. 4.</span></span>
+</div>
+
+<p><span class='pagenum'><a name="Page_20" id="Page_20">[Pg 20]</a></span></p><p>Lugs are provided on the bed and cylinder castings, and are bored to
+receive steel bolts&mdash;three are sufficient, provided the metal in and
+around these lugs is not pinched. In some cases a continuous flange is
+provided on both bed and cylinder, and a number of bolts inserted all
+the way round. This, however, is unnecessary, and has a somewhat clumsy
+appearance. When these bolts are tightened up, the cylinder and liner
+are clamped firmly to the bed; but the liner being free at the open end,
+can expand longitudinally without causing stresses in the cylinder
+casting.</p>
+
+<p>The combustion chamber K is virtually part of the cylinder, and has
+approximately equal to one-fourth the total volume of the cylinder. The
+shape varies somewhat in different makes of engines; in some it is
+rectangular, with all the corners well rounded off; in others it is
+practically a continuation of the cylinder, <i>i.e.</i>, it is circular in
+cross-section, with the back end more or less spherical; while, again,
+it is made slightly oval in cross-section; but in every case the corners
+should be <i>well</i> curved and rounded off, so that there is no one part
+which is liable to become heated disproportionately with the rest of the
+casting; in fact, in the whole cylinder casting there should be no
+sudden change, but a uniformity in the thickness of the metal employed.
+This point should be carefully remembered, although it applies more
+particularly to those parts of the casting subjected to higher
+temperatures than the rest.</p>
+
+<p>The main bearings are usually of brass or <span class='pagenum'><a name="Page_21" id="Page_21">[Pg 21]</a></span>gun-metal, and are adjusted
+for running in the same manner as any steam or other engines would be.
+The "brasses" are in halves, and are held down by the cast-iron caps, as
+shown in fig. 1.</p>
+
+<p>These bearings require extremely little attention, and do not show the
+wear and tear of running nearly so soon as the connecting-rod brasses.
+These, too, are usually of brass or gun-metal; but there are various
+forms of construction employed in connection with the back end or piston
+pin bearings. On very small engines the connecting rod is swollen at the
+back end in the forging, and then machined up and drilled, as shown in
+fig. 3. In this hole the brasses are inserted after being scraped up to
+a good fit on the piston pin.</p>
+
+<p>A flat is cut on one of the brasses, and a set screw is fitted, as
+shown, to prevent any movement of the latter after the final adjustment
+has been made. A lock nut should be used in conjunction with this set
+screw. Another method, and one more generally used on larger engines, is
+shown in fig. 4. In this case the brasses are larger than in the former,
+where they are virtually a split bush; here they have holes drilled in
+them to take the bolts, the latter usually and preferably being turned
+up to the shape shown in fig. 5.</p>
+
+
+
+<hr /><p><span class='pagenum'><a name="Page_22" id="Page_22">[Pg 22]</a></span></p>
+<h2><a name="CHAPTER_III" id="CHAPTER_III"></a>CHAPTER III</h2>
+
+<h3>HOW A GAS ENGINE WORKS</h3>
+
+
+<p>The gas engine of the present day, although from a structural point of
+view is very different to the early engine, or even that of fifteen
+years ago, is, in respect to the principle upon which it works, very
+similar. The greater number of smaller power engines in use in this
+country work on what is known as the Otto or four-cycle principle; and
+it is with this class of engine we propose to deal.</p>
+
+<p>Reference to the various diagrams in the text will help considerably,
+and make it an easy matter for any reader hitherto totally unacquainted
+with such engines to see why and how they work.</p>
+
+<p>Coal-gas consists primarily of five other gases, mixed together in
+certain proportions, these proportions varying slightly in different
+parts of the country:&mdash;Hydrogen (H), 50; marsh gas (CH<sub>4</sub>), 38;
+carbon-monoxide, 4; olefines (C<sub>6</sub>H<sub>4</sub>), 4; nitrogen (N), 4.</p>
+
+<p>Gas <i>alone</i> is not explosive; and before any practical use can be made
+of it, a considerable quantity of<span class='pagenum'><a name="Page_23" id="Page_23">[Pg 23]</a></span> air has to be added, diluting it down
+to approximately ten parts air to one of pure gas. This mixture is <i>now</i>
+highly explosive.</p>
+
+<p>The reader will do well to bear these facts constantly in mind,
+especially when he is repairing, adjusting, or experimenting with a gas
+engine. We wish to emphasise this at the outset, because a consideration
+of these facts will keep cropping up throughout all our dealings with
+the gas engine, and if once a fairly clear conception is obtained of how
+gas will behave under certain and various conditions, half, or even more
+than half, our "troubles" will disappear; the cry that the gas engine
+has "gone wrong" will be heard less often, and users would soon learn
+that the gas engine is in reality as worthy of their confidence as any
+other form of power generator in common use.</p>
+
+<p>But to revert to the explanation of the cycle of operations. The cycle
+is completed in four strokes of the piston, <i>i.e.</i>, two revolutions of
+the crank shaft.</p>
+
+<p>At the commencement of the first out-stroke (the charging or suction
+stroke) gas and air are admitted to the cylinder through the respective
+valves (fig. 6), and continue to be drawn in by what may be termed the
+sucking action of the piston, until the completion of this stroke (the
+<i>precise</i> position of the closing and opening of the valves will be
+referred to later on). The next stroke (fig. 7) is the compression
+stroke. All the valves are closed whilst the piston moves inwards,
+compressing the gases, until at the end of this stroke, and at the
+instant of maximum <span class='pagenum'><a name="Page_24" id="Page_24">[Pg 24]</a></span>compression, the highly explosive charge is fired by
+means of the hot tube or an electric spark, as the case may be. The
+ensuing stroke&mdash;the second out-stroke of the cycle&mdash;is the result of the
+explosion, the expanding gases driving the piston rapidly before them;
+this, then, is the expansion, or working stroke (fig. 8.)</p>
+
+<div class="figcenter" style="width: 450px;">
+<img src="images/image6.jpg" width="450" height="160" alt="Fig. 6." title="" />
+<span class="caption"><span class="smcap">Fig. 6.</span>&mdash;Commencement of first out-stroke suction or
+charging stroke. Gas and air valve about to open.</span>
+</div>
+
+<div class="figright" style="width: 450px;">
+<img src="images/image7.jpg" width="450" height="160" alt="Fig. 7." title="" />
+<span class="caption"><span class="smcap">Fig. 7.</span>&mdash;Compression stroke, during which all valves
+remain closed.</span>
+</div>
+
+<p>During the last&mdash;the second inward&mdash;stroke (fig. 9) the exhaust valve is
+opened, and the returning piston sweeps all the burnt gases (the product
+of combustion) out into the exhaust pipe and so into the atmosphere.
+This completes the cycle, and the piston, crank, and valves are in the
+same relative positions as formerly, and the same series of operations
+is repeated again and again. Of course, it is not always the case that
+both air <i>and</i> gas valve are opened on the charging stroke; that depends
+upon<span class='pagenum'><a name="Page_25" id="Page_25">[Pg 25]</a></span> the method employed to govern the speed of the engine. Supposing
+it were governed on the hit and miss principle (to be explained
+hereafter), the gas valve would be allowed to remain closed during the
+charging stroke, and air alone would be drawn into the cylinder, then
+compressed, but not being explosive would simply expand again on the
+working stroke, giving back nearly all the energy which was absorbed in
+compressing it, and finally be exhausted in the same manner as the burnt
+gases are.</p>
+
+<div class="figleft" style="width: 450px;">
+<img src="images/image8.jpg" width="450" height="153" alt="Fig. 8." title="" />
+<span class="caption"><span class="smcap">Fig. 8.</span>&mdash;Second out stroke, showing position of valves
+during working stroke.</span>
+</div>
+
+<div class="figright" style="width: 450px;">
+<img src="images/image9.jpg" width="450" height="153" alt="Fig. 9." title="" />
+<span class="caption"><span class="smcap">Fig. 9.</span>&mdash;Second inward stroke, showing position of valves
+during the exhaust stroke.</span>
+</div>
+
+<div class="figcenter" style="width: 450px;">
+<img src="images/image10.jpg" width="450" height="153" alt="Fig. 10." title="" />
+<span class="caption"><span class="smcap">Fig. 10.</span>&mdash;First out-stroke, showing position of valves
+during the charging stroke.</span>
+</div>
+
+<p><span class='pagenum'><a name="Page_26" id="Page_26">[Pg 26]</a></span></p><p>Fig. 10 shows diagrammatically the position of crank, piston, and
+valves <i>during</i> the charging stroke.</p>
+
+<div class="figcenter" style="width: 500px;">
+<img src="images/image11.jpg" width="500" height="668" alt="Fig. 11." title="" />
+<span class="caption"><span class="smcap">Fig. 11.</span>&mdash;Cross Section of Cylinder.</span>
+</div>
+
+<p>In figs. 1 and 2 we gave drawings of two gas engines, which are typical
+examples of modern practice. Huge strides have been made in recent years
+in gas-engine work, as regards both workmanship and efficiency, so that
+to-day we have in the gas engine a machine whose mechanical efficiency
+compares favourably with that of any other power generator, and whose
+thermal efficiency is very much greater.</p>
+
+<p><span class='pagenum'><a name="Page_27" id="Page_27">[Pg 27]</a></span></p>
+<div class="figcenter" style="width: 500px;">
+<img src="images/image12.jpg" width="500" height="552" alt="Fig. 12." title="" />
+<span class="caption"><span class="smcap">Fig. 12.</span>&mdash;Longitudinal Section of Cylinder.</span>
+</div>
+
+<p><span class='pagenum'><a name="Page_28" id="Page_28">[Pg 28]</a></span></p><p>Figs. 11 and 12 show respectively a sectional end and side elevation of
+the cylinder, from which it will not be difficult for the reader,
+however unacquainted he may be with gas-engine work, to see how the
+various requirements and peculiarities of the engine should be
+considered and provided for.</p>
+
+<p>A most important desideratum in any machine or engine is that it shall
+be as simple in construction as ever possible; complicated mechanism
+should only be introduced when such addition or complication compensates
+adequately for what must necessarily be a higher first cost, and
+incidentally the greater wear and tear and attention involved. Figs. 11
+and 12 show what has been done to simplify the construction of the gas
+engine in recent years. The main feature in this case is the very
+get-at-able position of the two main valves&mdash;the air valve F and the
+exhaust E. These valves, as may be seen from the drawing, are capable of
+withdrawal after the cover of the combustion chamber has been removed.
+The latter is an iron casting, shaped and faced up to make an absolutely
+tight joint; no asbestos or any packing is used to make this joint&mdash;and
+is held in place by four studs, as shown. Thus, all that is necessary is
+to remove the four nuts, lift the cover off, then pull out the pins
+which keep the spiral springs in position, and withdraw the valves. The
+latter are seated direct on to the metal of the cylinder casting, the<span class='pagenum'><a name="Page_29" id="Page_29">[Pg 29]</a></span>
+gun-metal bushes A and B acting as guides. Further reference to A (the
+mixer), which serves a twofold purpose, will be made later on.</p>
+
+<p>The gas valve and cock are mounted in a separate casting, which is
+carried by a couple of studs, the joint between this and cylinder being
+made with a piece of rubber insertion. The gas enters at the gas-cock,
+passes through the valve and port G, and round the annular space in the
+bush or "mixer" A, previously mentioned, and thence through a number of
+small holes in same, immediately below the seat of the air valve F. At
+the same time, pure air is drawn in <i>via</i> the air box (as explained
+hereafter), through port L (fig. 11), and thence up the centre of bush A
+and over the small holes through which the gas is flowing. The two then
+thoroughly mix and enter the combustion chamber together as the air
+valve F is opened. This device produces a perfectly homogeneous mixture,
+which conduces in no small measure to perfect combustion when the
+explosion takes place, and upon which, to a very great extent, depends
+the efficiency of the engine. Besides possible loss in this direction,
+however, there is another source of waste which cannot be eliminated,
+and that is the heat taken away by the cooling water which surrounds the
+cylinder. As this loss is inevitable, the best thing we can do is to
+make it as small as possible. Theoretically, it would be no small
+advantage if we could work at very much higher temperatures than we do
+at the present time, and it is only certain mechanical difficulties
+which bar the way and so effectually<span class='pagenum'><a name="Page_30" id="Page_30">[Pg 30]</a></span> prevent the already high thermal
+efficiency of the engine being greatly increased.</p>
+
+<p>It is no easy matter to overcome these difficulties completely, but
+improvements in this direction are continually being made, so that
+troubles which attended the gas-engine user years ago no longer exist.</p>
+
+<p>All that we require of the cooling water is that it shall keep certain
+working parts of the engine at a reasonable temperature; for instance,
+the cylinder must not be so hot as to deprive the lubricating oil of its
+property to lubricate, neither must the exhaust valve become so hot as
+to cause it to seize in the bush and stick up; but, beyond such
+considerations as these, the higher the temperature is at the
+commencement of each explosion the more efficient will the engine be.
+The object, then, is to do as little cooling as possible, and to apply
+the cooling effect at the right parts; hence the passages and chambers
+through which the cooling water circulates should be so arranged that
+those which require to be kept at a low temperature are in close
+proximity to the cooling water. On some of the engines of days gone by,
+the exhaust valve was carried in a large iron casting, this in turn
+being bolted to the cylinder casting and communicating with the
+combustion chamber by means of a port. Such an arrangement was found to
+be not only clumsy but inefficient; the water passages were small and
+difficult to get at; they readily furred up; and moreover, the joint
+between this casting and the cylinder was<span class='pagenum'><a name="Page_31" id="Page_31">[Pg 31]</a></span> necessarily a water <i>and</i>
+explosion joint, and the fewer we have of these the better.</p>
+
+<p>The method&mdash;if it may be called a method&mdash;of overcoming or preventing
+the exhaust valve becoming too hot is, in the case of figs. 11 and 12,
+simply one of judicious arrangement and design. The cooling water enters
+by the inlet K (fig. 11), and circulates round the exhaust valve port X
+and valve E immediately, before becoming heated, thus keeping the
+hottest of the working parts of the engine at a suitable temperature;
+and the valve seat, being in direct metallic communication with the cold
+water, does not become burnt or pitted. On the other side of the exhaust
+valve we have the air valve and its passages, through which cool air is
+continually being drawn; this also helps to keep the exhaust valve cool.</p>
+
+<p>From this, then, we may conclude that overheating of the cylinder will
+not occur under normal conditions, given an engine of good design; but,
+if this trouble does arise, we may safely look first of all for some
+defect in the cooling water circulation. Some waters contain a greater
+amount of impurities than others, and consequently the water space may
+furr up more rapidly in one district than in another. But this deposit,
+even under the worst conditions, accumulates very slowly, and the
+operation of cleaning out the water-jacket is a very infrequent
+necessity. The exhaust valve, however, may become overheated if it is
+allowed to get into bad condition, <i>i.e.</i>, leaky. Its seat should be
+well looked after, or<span class='pagenum'><a name="Page_32" id="Page_32">[Pg 32]</a></span> the hot gases will blow past when it is
+presumably shut; and if this defect, slight though it may be to begin
+with, is allowed to develop, both the seat, the valve head, and the
+spindle will become burnt away and pitted, perhaps badly, due to the
+excessive heat.</p>
+
+
+
+<hr /><p><span class='pagenum'><a name="Page_33" id="Page_33">[Pg 33]</a></span></p>
+<h2><a name="CHAPTER_IV" id="CHAPTER_IV"></a>CHAPTER IV</h2>
+
+<h3>IGNITION DEVICES</h3>
+
+
+<p>The ignition devices commonly employed may be divided into three main
+classes&mdash;the metal tube, the porcelain tube, and the electric ignition.
+These again may be subdivided: The first being either iron or nickel
+(hecknum as they are sometimes called); the second are of two
+kinds&mdash;single-ended and double-ended; and the third takes many forms
+which many of my readers are possibly well acquainted with, such as the
+magneto, the induction coil and trembler, and the high-tension magneto
+ignition, the latter device having been used successfully on various
+occasions, though not yet universally adopted.</p>
+
+<p>The first-named have one or two advantages over the nickel tube. They
+are very inexpensive, and are easily heated to the required temperature;
+moreover, they can be made at home, should occasion demand. On the other
+hand, they are not so durable, have a very uncertain life, and
+consequently need renewing frequently&mdash;their average life being<span class='pagenum'><a name="Page_34" id="Page_34">[Pg 34]</a></span> not
+more than 60 working hours. Fig. 13 gives an outline drawing of an iron
+tube, with its burner and chimney fixed in position. The tube is very
+similar to a piece of <span class="above">1</span>&#8260;<span class="below">4</span>-in. gas-barrel, closed up at one end and a
+taper thread (<span class="above">1</span>&#8260;<span class="below">4</span>-in. gas) cut on the other; in fact, gas-barrel may be
+used for making these tubes at home&mdash;and measure about 7 or 8 in. over
+all It is screwed into a firing block, which in turn is screwed into the
+combustion chamber end, so that when right home it is in such position
+that the tube stands quite vertical. The section of the tube, fig. 13,
+shows the condition it gets into after having been in use some time. The
+bore, it will be seen, has become almost completely closed up, so that
+there is practically no communication between the hot part of the tube
+and the combustion chamber. This closing up of the bore is very gradual,
+and<span class='pagenum'><a name="Page_35" id="Page_35">[Pg 35]</a></span> it is in the early stages of this process that erratic firing is
+likely to occur; sometimes the charge will be successfully fired and
+sometimes not. It may be as well to mention here that the length of the
+tube, although to a certain extent immaterial, should neither be
+excessively long nor abnormally short, the precise length varying with
+the size of the engine. A <span class="above">1</span>&#8260;<span class="below">4</span>-in. tube, 8 ins. long, may be used
+successfully on engines ranging from <span class="above">1</span>&#8260;<span class="below">2</span> to 6 horse-power, provided a
+suitable burner is fitted enabling the tube to be heated at any required
+spot. After the first charge has been fired, and the exhaust takes
+place, practically all the burnt gases are cleared out of the cylinder,
+but a small amount of these will generally remain in the tube and the
+bore of the<span class='pagenum'><a name="Page_36" id="Page_36">[Pg 36]</a></span> firing block. On the ensuing compression stroke these inert
+gases are compressed to the far end of the tube, thus making way for the
+explosive mixture to reach the hot portion, and explode, thus sending a
+jet of flame into the main volume of the mixture which is immediately
+ignited. Hence there is no advantage in having a tube too long, while,
+on the other hand, it <i>must</i> not be too short.</p>
+
+<div class="figleft" style="width: 300px;">
+<img src="images/image13.jpg" width="300" height="594" alt="Fig. 13." title="" />
+<span class="caption"><span class="smcap">Fig. 13.</span></span>
+</div>
+
+<div class="figright" style="width: 250px;">
+<img src="images/image14.jpg" width="250" height="254" alt="Fig. 14." title="" />
+<span class="caption"><span class="smcap">Fig. 14.</span></span>
+</div>
+
+<div class="figcenter" style="width: 450px;">
+<img src="images/image15.jpg" width="450" height="337" alt="Fig. 15." title="" />
+<span class="caption"><span class="smcap">Fig. 15.</span></span>
+</div>
+
+<p>The asbestos lining, shown in fig. 13, may be of various thicknesses,
+according to the size of the chimney and the tube; the reason for this
+will be apparent to many; but being a most important factor in the
+heating of the tube, and consequently the working of the engine, it will
+be advisable to deal with this point more fully.</p>
+
+<p>Due mainly to the peculiar behaviour of iron tubes under heat and
+internal pressure, it is always advisable to look to them first of all
+when the engine shows signs of missing fire; and to always examine the
+bore of a fresh one, and ascertain that it is perfectly clear before
+putting it in. The adjustment of the ignition tube, although one of the
+most important and necessary to be made on the whole engine, is in
+itself a perfectly simple matter. It must be understood that the
+ignition tube cannot, with the ordinary means at our disposal, be kept
+at too high a temperature; but it must not be assumed that either the
+<i>size</i> of the flame, or the <i>time</i> the flame has been alight, is
+conclusive evidence that the tube is, or ought to be, sufficiently hot
+to fire the charge successfully. It is an uncommon<span class='pagenum'><a name="Page_37" id="Page_37">[Pg 37]</a></span> thing to hear a man
+exclaim&mdash;after it has been pointed out that his tube is practically
+cold&mdash;"Why, it's been alight for hours!"</p>
+
+<p>If such is the case with you, reader, you may very rightly assume that
+the burner is not properly adjusted, and so does not give the <i>right
+kind of flame</i>.</p>
+
+<p>In order to get the hottest possible flame, the quantity of gas and air
+must be mixed in the right proportions. A common fault is that there is
+too much gas allowed to flow through the nipple, compared with the
+amount of air being drawn in at the air aperture, fig. 13. The result
+is, we get a flame of great length, but one which is not at all suited
+to our requirements; and instead of giving up its heat to the tube and
+the asbestos lining of the chimney, a large amount of gas we are
+presumably burning <i>in</i> the chimney is not being burnt there at all,
+for, on applying a light just above the chimney top, a quantity of this
+gas we are wasting will be seen to burn with a flickering blue flame.</p>
+
+<p>To put matters right, it is necessary to do one of two things&mdash;either
+cut down the supply of gas or increase the air-supply. Providing the air
+aperture is normal, <i>i.e.</i>, the same size as it was originally, it is
+better to adjust the <i>gas</i>, which may be done by tapping up the nipple
+N, as indicated in the enlarged sketch, fig. 14, until just the right
+amount of gas can flow.</p>
+
+<p>As a rule, if there is too much air, the flame will burn with a loud
+roaring noise, and is liable to fire back. The nipple should then be
+opened out with<span class='pagenum'><a name="Page_38" id="Page_38">[Pg 38]</a></span> a small reamer&mdash;the tang of a small file, ground to a
+long taper point, makes an admirable tool for this purpose. Whether the
+burner is of the ordinary bunsen type, or the ring or stove type, the
+above remarks apply, as in every case the flow of gas is governed by the
+size of the orifice through which it flows.</p>
+
+<p>There is no need to use anything beyond a touch of oil when putting in a
+new tube, in order to make a perfectly tight joint; white or red lead
+are quite unnecessary, and are liable to make it a troublesome matter to
+remove the tube on future occasions. Neither should undue force be
+applied when putting in new tubes; it is liable to wear the thread in
+the firing block, which results in a partial stoppage of the ignition
+hole, as indicated in fig. 15. This is especially the case if we happen
+to get hold of a tube with its screwed part slightly smaller than usual.</p>
+
+<p>The asbestos with which the chimney is lined should be about <span class="above">1</span>&#8260;<span class="below">8</span> in.
+thick, and, when renewing, the same thickness should be used as
+originally. A thicker board will reduce the annular space round the
+tube, and will have a choking effect on the flame&mdash;much the same as
+referred to above, when there is too much gas and not enough air. A
+simple method of lining the chimney is to cut a block of wood to the
+inside dimensions of the chimney, less <span class="above">1</span>&#8260;<span class="below">4</span> in. in width and thickness,
+then soften the asbestos cardboard by immersing in water, and bend it
+round the wood, cutting off to the required size, <i>i.e.</i>, till the two
+edges form a neat butt joint. It can be allowed<span class='pagenum'><a name="Page_39" id="Page_39">[Pg 39]</a></span> to remain on the mould
+until dry&mdash;when it will retain its shape&mdash;or can be put into the chimney
+straight away, if it is wanted for use immediately. In the latter case,
+however, it will be some fifteen minutes or so before the tube will
+attain its working temperature. Asbestos linings gradually become worn
+and ragged, and small flakes are apt to detach themselves and fall down
+into the burner, which, of course, prevents the flame playing as it
+should around the tube. In such cases it is not always necessary to fit
+a new lining; if the chimney is removed, the loose flakes shaken out and
+the asbestos well damped and patted down with a wooden or steel
+foot-rule or other suitably shaped tool, it will be fit for another long
+spell of work.</p>
+
+<p>The nickel or hecknum tubes are treated in the same manner as the iron,
+but, as we mentioned before, are more durable, but require more heating
+to get them up to a workable temperature. Their greater first cost is
+compensated to some extent by makers in some cases guaranteeing them for
+six months.</p>
+
+<p>Of the porcelain ignition devices, we will deal with the double-ended
+tube first, it being the more commonly used of the two in this country.
+This form of tube is usually about 3 in. long, <span class="above">1</span>&#8260;<span class="below">2</span> in. diameter, and
+open at both ends. It may be mounted in a metal casting, in form not
+unlike the small gas stoves for heating soldering irons. It is heated
+the greater part of its length by a couple of rows of gas jets, and is
+frequently surrounded by<span class='pagenum'><a name="Page_40" id="Page_40">[Pg 40]</a></span> an asbestos lining. The whole arrangement is
+in reality a tiny furnace. When in position for working, one end of the
+tube is open to the ignition passage leading and communicating with the
+combustion chamber, while the other end is sealed, through butting up
+against a metal cap or plate. An asbestos washer is interposed between
+the tube at each end and the metal it bears against, thus making a more
+or less flexible joint. A thumb screw is arranged at the outside end of
+the tube, by means of which pressure can be applied to clamp it up
+between the washers to the desired extent. Some care has to be exercised
+in adjusting this form of tube for running. When heated to the working
+temperature it, of course, expands, so that, if tightened up too much
+when cold, it is under a fairly high compression; and when the engine is
+started, and the explosion takes place, it not infrequently bursts, if
+there is not sufficient "give" in the washers to allow for the
+expansion. On the other hand, if not clamped up sufficiently tight to
+start with, when the explosion occurs, the washer at one or each end is
+blown out. This adjustment has to be made to a nicety, and, although a
+somewhat difficult matter, success may be attained after one or two
+trials. It is advisable, after a new tube has been put in, to start up
+the engine gently, <i>i.e.</i>, with less than the normal supply of gas, and
+increase to the full amount gradually whilst running. This may be done
+by simply opening the gas-cock on engine partially in the first place.</p>
+
+<p><span class='pagenum'><a name="Page_41" id="Page_41">[Pg 41]</a></span></p><p>The single-ended porcelain tube is not so well known here as on the
+continent; why, we cannot say; certainly it is preferable in every way.
+We give a few illustrations, showing the method of using this tube.</p>
+
+<p>Figs. 16 and 17 show the general arrangement of tube and chimney and the
+manner in which they are fixed to the cylinder. The device consists
+primarily of three parts&mdash;the body or chimney B, the cover C, and the
+tube itself T. The body is a light iron casting, carried by a couple of
+studs SS, which are either screwed into the firing block F, or direct
+into the metal of the cylinder casting if no firing-block is used; the
+latter may very well be dispensed with in the smaller-sized engines.</p>
+
+<p>The tube is made of thin porcelain, slightly bell-mouthed at its open
+end, and is mounted in a thick metal washer W, as shown in fig. 18 in
+section, the joint being made with a little asbestos paper, moistened.</p>
+
+<p>The block F and the face of the body B (fig. 16) are recessed to take
+the washer W easily, but the depth of both recesses taken together must
+be about <span class="above">1</span>&#8260;<span class="below">16</span> in. less than the thickness of the washer W; thus, when
+the tube is placed in position between the body B and the block F, and
+the former screwed up by means of the two nuts, as shown in the figure
+16, the effect is to clamp the <i>washer</i> which carries the tube, but <i>not
+the porcelain tube itself</i>.</p>
+
+<p><span class='pagenum'><a name="Page_42" id="Page_42">[Pg 42]</a></span></p>
+
+<div class="figleft" style="width: 400px;">
+<img src="images/image16.jpg" width="400" height="580" alt="Fig. 16." title="" />
+<span class="caption"><span class="smcap">Fig. 16.</span></span>
+</div>
+
+<div class="figright" style="width: 400px;">
+<img src="images/image17.jpg" width="400" height="681" alt="Fig. 17." title="" />
+<span class="caption"><span class="smcap">Fig. 17.</span></span>
+</div>
+
+<div class="figcenter" style="width: 350px;">
+<img src="images/image18.jpg" width="350" height="774" alt="Fig. 18." title="" />
+<span class="caption"><span class="smcap">Fig. 18.</span></span>
+</div>
+
+<p><span class='pagenum'><a name="Page_43" id="Page_43">[Pg 43]</a></span></p><p>The latter is left perfectly free to expand; and yet, owing to its
+particular shape, the pressure in the cylinder during the compression
+and explosion stroke only tends to make the joint between the tube and
+washer more secure. The action of this ignition device depends upon the
+tube heater H, which is merely a small bunsen burner, the flame of which
+impinges on the tube at one particular spot, raising it to a very high
+temperature&mdash;almost white heat. Most of my readers will know the
+formation of the bunsen flame. It in composed of two distinct zones. The
+inner one, marked A in fig. 18, is a perfectly cold part of the flame,
+and appears to be a pale-blue coloured cone.</p>
+
+<p>It is the outer zone which is the hot portion of the flame, hence this
+part <i>only</i> must be allowed to play on the tube. The tip of the blue
+cone A must be kept about <span class="above">1</span>&#8260;<span class="below">4</span> in. below the tube, in order to ensure the
+hottest part of the flame impinging precisely where the heat is
+required.</p>
+
+<p>The total length of the whole flame is, to a certain extent, immaterial;
+but, generally speaking, it should be adjusted so that the length of the
+inner cone A is about 1 in. or 1-<span class="above">1</span>&#8260;<span class="below">4</span> in. The same methods which we
+described in the early part of this chapter can be employed in the
+adjustment of this burner, but some care should be exercised to get the
+correct flame length.</p>
+
+<p>The result of allowing the cold part of the flame to impinge on the tube
+is observable in fig. 18. The black spot indicated on the drawing
+actually appears as a black or sooty spot when looking at the tube under
+these conditions; but in reality no discoloration whatever takes place,
+the spot <span class='pagenum'><a name="Page_44" id="Page_44">[Pg 44]</a></span>disappearing immediately the cone A is made shorter, or the
+burner H lowered in the chimney B, so that the tip of A is just below,
+and does not touch the tube at all.</p>
+
+<p>The adjustment of the length of cone A may be accomplished in two
+ways&mdash;(1) by keeping the supply of gas constant, and varying the amount
+of air admitted at aperture K, fig. 18; (2) by keeping the supply of air
+constant, and varying the amount of gas admitted through nipple N. The
+first method is to be preferred when it is necessary to make any slight
+adjustment due to the variation of gas pressure during the day, and may
+be accomplished by fitting a small sliding shield G, as shown in the
+figs. 16 and 17, and moving it round so that it covers, more or less,
+the aperture K. Thus the length of cone A may be adjusted to a nicety in
+a very few seconds. This shield keeps all draughts and puffs of wind
+from the fly-wheel away from the aperture, and helps the flame to burn
+very steadily. In the first place, of course, the flame will be
+regulated by opening out or tapping up the nipple N (an enlarged sketch
+of which is given in fig. 14), so that cone A is just about 1-<span class="above">1</span>&#8260;<span class="below">4</span> in.
+long when air aperture is full open; but once this is done, any future
+adjustment can be made by throttling the air-supply, or raising or
+lowering the burner bodily, the set screw keeping it in any desired
+position (see fig. 17).</p>
+
+<p>From the foregoing remarks it will be seen that the most noteworthy
+features of this form of ignition<span class='pagenum'><a name="Page_45" id="Page_45">[Pg 45]</a></span> are the ease and certainty with which
+the tube can be fixed in a few moments; that when the two nuts on the
+studs SS have been tightened up there is no likelihood of the joints
+being "blown," for, as we said before, only the metal washer is clamped
+up, the porcelain tube itself being as free to expand as it was before.
+It is also at once obvious when any adjustment of the flame is
+necessary; there need be no uncertainty as to whether the tube is hot
+enough or not.</p>
+
+
+
+<hr /><p><span class='pagenum'><a name="Page_46" id="Page_46">[Pg 46]</a></span></p>
+<h2><a name="CHAPTER_V" id="CHAPTER_V"></a>CHAPTER V</h2>
+
+<h3>MAGNETO IGNITION</h3>
+
+
+<p>The third form of ignition we have to deal with is the electric.</p>
+
+<p>There are a great number of different types made and used, but for
+gas-engine use perhaps that known as the magneto ignition is the most
+satisfactory. With this form, neither accumulators, dry batteries, or
+spark coils are required, and consequently a greater simplicity is
+arrived at than would otherwise be the case.</p>
+
+<p>In fig. 19 we show diagrammatically the ordinary form of magneto
+machine. Virtually it is a small dynamo which is fixed to the side of
+cylinder casting, and is operated in the manner shortly to be described.
+As we do not propose to enter into more than a brief explanation of why
+and how this apparatus generates current to produce the required spark,
+perhaps a simple analogy will make matters most intelligible to any
+reader not well acquainted with electrical phenomena. We know that when
+a current of electricity is flowing in a wire, and the wire be<span class='pagenum'><a name="Page_47" id="Page_47">[Pg 47]</a></span> suddenly
+broken, a spark will occur at the point of breakage. This fact may be
+observed in an ordinary electric bell when ringing; at the tip of the
+contact breaker a number of tiny sparks may be seen to occur, due to the
+rapid make and break of the current flowing in the circuit. Precisely
+the same action takes place in our magneto-igniter, but, instead of a
+multitude of tiny sparks, we produce one at a time, at definite
+intervals, viz., at the commencement of each explosion stroke.</p>
+
+<div class="figcenter" style="width: 450px;">
+<img src="images/image19.jpg" width="450" height="305" alt="Fig. 19." title="" />
+<span class="caption"><span class="smcap">Fig. 19.</span></span>
+</div>
+
+<p>In the later form of magneto machines there is a soft iron sleeve
+between the magnet poles and the armature. The former is connected to a
+system of levers by which a reciprocating motion is imparted to it by
+means of a suitably arranged cam on the side shaft. It has been found
+that better results are obtained by causing the magnetic field to move<span class='pagenum'><a name="Page_48" id="Page_48">[Pg 48]</a></span>
+relative to the armature winding than to move the latter through a
+stationary field. Reference to the diagrams, figs. 20 and 21, will make
+this clear.</p>
+
+<p>In fig. 19 the cam C is shown just on the point of allowing the lever L
+to fly back into its normal position, due to the action of the springs
+comprising a dashpot S. As the cam rotates, it pushes the lever L to the
+left, the sleeve (or virtually the armature A) is also rotated through a
+portion of a revolution comparatively slowly; but as soon as L is
+released, the sleeve (or armature) flies back again almost
+instantaneously and for the moment is generating a current in the same
+manner as would any ordinary continuous current dynamo.</p>
+
+<div class="figcenter" style="width: 400px;">
+<img src="images/image20.jpg" width="400" height="632" alt="Fig. 20." title="" />
+<span class="caption"><span class="smcap">Fig. 20.</span></span>
+</div>
+
+<div class="figcenter" style="width: 400px;">
+<img src="images/image21.jpg" width="400" height="632" alt="Fig. 21." title="" />
+<span class="caption"><span class="smcap">Fig. 21.</span></span>
+</div>
+
+<p><span class='pagenum'><a name="Page_49" id="Page_49">[Pg 49]</a></span></p><p>At the instant the maximum current is being generated, the circuit is
+broken by means of the contact breaker D, fig. 19, which we show in
+detail in fig. 22. The latter is mounted on the end of the combustion
+chamber, and consists of two parts, D and P.</p>
+
+<div class="figcenter" style="width: 400px;">
+<img src="images/image22.jpg" width="400" height="618" alt="Fig. 22." title="" />
+<span class="caption"><span class="smcap">Fig. 22.</span></span>
+</div>
+
+<p>D is an easy fit in the hole bored to receive it, and has a mushroom
+valve head and seating, as shown, so that it moves readily when struck
+by the projection E on the rod R (fig. 19); but yet, acting in the
+manner of a non-return valve, it allows no gas to<span class='pagenum'><a name="Page_50" id="Page_50">[Pg 50]</a></span> escape when the
+explosion takes place in the cylinder. D is therefore in direct metallic
+communication with the engine frame and earth.</p>
+
+<p>P is a fixed metal pin, carefully insulated from all contact with the
+engine frame and earth. To this pin one end of the armature winding is
+connected, whilst the other end is connected to the engine frame.</p>
+
+<p>Thus a closed circuit is formed, and when the current is generated it
+flows from one terminal of magneto through wire to pin P, on to D,
+through D to earth (<i>i.e.</i>, engine frame), and so back to other terminal
+on magneto.</p>
+
+<p>And as the circuit is broken between D and P, we obtain a spark, as
+previously explained, which may be timed to take place by adjusting the
+position of cam C on side shaft relatively to the position of piston.</p>
+
+<p>It may be said that the position of the magneto-igniter is immaterial;
+it will be fixed in different positions on different types of engines,
+and so long as the operating mechanism is simple and effective, <i>i.e.</i>,
+as direct as is practicable, it works well, and requires little
+attention. The timing of the spark will be dealt with in the chapter on
+Cams and Valve Settings.</p>
+
+
+
+<hr /><p><span class='pagenum'><a name="Page_51" id="Page_51">[Pg 51]</a></span></p>
+<h2><a name="CHAPTER_VI" id="CHAPTER_VI"></a>CHAPTER VI</h2>
+
+<h3>GOVERNING</h3>
+
+
+<p>The devices for governing the speed of the engine may be divided,
+broadly speaking, into two classes&mdash;the inertia or hit and miss
+governor, and the centrifugal. Of the latter type we will give an
+instance first. In figs. 23 and 24 the governor gear is shown
+diagrammatically, consisting of a couple of weights WW suspended from a
+vertical spindle. These fly apart when caused to revolve by the bevel
+wheel gearing BB, and raise the sleeve S to a greater or lesser extent.
+A recess in the latter engages a lever arm L, through which the vertical
+movement of the sleeve S is converted into a horizontal movement of the
+sleeve T. The latter is carried by the valve lever P, and is virtually a
+roller which engages with one or other of the steps of the cam C,
+according to the speed of the engine. The object of this arrangement is
+to keep the ratio of air to gas uniform throughout all variations of
+load. The gas and air valve are shown as both being operated by the same
+lever P, the accurate timing of the latter being obtained by means of
+set screws.</p>
+
+<p><span class='pagenum'><a name="Page_52" id="Page_52">[Pg 52]</a></span></p>
+<div class="figcenter" style="width: 450px;">
+<img src="images/image23.jpg" width="450" height="723" alt="Fig. 23." title="" />
+<span class="caption"><span class="smcap">Fig. 23.</span></span>
+</div>
+
+<p><span class='pagenum'><a name="Page_53" id="Page_53">[Pg 53]</a></span></p>
+<div class="figcenter" style="width: 450px;">
+<img src="images/image24.jpg" width="450" height="711" alt="Fig. 24." title="" />
+<span class="caption"><span class="smcap">Fig. 24.</span></span>
+</div>
+
+<p><span class='pagenum'><a name="Page_54" id="Page_54">[Pg 54]</a></span></p><p>Messrs Dougill &amp; Co.'s engines are fitted with a step down cam and
+governor such as this. The centrifugal governor is often arranged so
+that instead of the charge being merely reduced in volume, the whole
+charge is cut out, and no explosion whatever takes place. (In this
+respect the same results are obtained as when a hit and miss governor is
+used, and the latter form therefore is to be preferred, especially on
+small engines, where the difference between the indicated power and the
+brake power is always, even under the best conditions, fairly great.)</p>
+
+<p>In this case the governor lever only operates the gas valve; the air
+valve being opened on every charging or suction stroke, whether gas is
+admitted or not.</p>
+
+<p>Another application of the centrifugal governor is to suspend a distance
+piece on the end of the governor lever, so that at normal speed this
+distance piece is interposed between the gas valve spindle and the lever
+operating it. In that case the gas valve will be opened. But if the
+speed is above the normal, the distance piece will be raised clear of
+the valve spindle, and the opening mechanism (driven by a cam on the
+side shaft) will simply move forward and recede again without ever
+touching the gas valve.</p>
+
+<p>There are any number of movements which have been, and there are many
+more which could be, devised to give the same result; and it depends
+principally upon the form of engine in question which device we adopt.</p>
+
+<p>The simplest and most direct action is, however,<span class='pagenum'><a name="Page_55" id="Page_55">[Pg 55]</a></span> always the best;
+complicated mechanism is to be deprecated, especially on small engines.
+For this reason is the inertia governor more generally fitted to such
+engines.</p>
+
+<div class="figcenter" style="width: 400px;">
+<img src="images/image25.jpg" width="400" height="851" alt="Fig. 25." title="" />
+<span class="caption"><span class="smcap">Fig. 25.</span></span>
+</div>
+
+<p>A simple form of this governor is shown in fig. 25. The gas valve V is
+shown on its seating. It is screwed into a pecker block B, and pinned as
+shown. The latter should be of cast steel, tempered to a straw colour;
+or if mild steel or iron is used, it must be well case-hardened, in
+order to resist wear. The pecker P (also tempered hard) is mounted on
+the cast-iron weight W, which in turn is pivoted on the valve lever L.
+It will be seen that the weight W (which is only held in the position
+shown by the spring S) will tend to lag behind when a sudden upward
+motion is imparted to the lever L.<span class='pagenum'><a name="Page_56" id="Page_56">[Pg 56]</a></span> Thus it depends upon the degree of
+suddenness with which L moves whether the pecker P remains in the same
+relative position to the lever as the latter travels upwards and engages
+with the pecker block B, or whether it misses it and simply slides over
+the face of the block. The adjustment of the spring S is effected by
+screwing up or slacking out the milled nuts T; and on the degree to
+which this spring is compressed depends the sensitiveness of the
+governor, and consequently the speed of the engine. To obtain accurate
+and steady governing with this type of mechanism it is essential that
+the weight be perfectly free on its spindle, and that nothing but the
+spring S holds, or tends to hold, it in the position shown. On this
+account it is advisable to provide a "lip" on the pecker block, as
+shown, to keep the area of contact as small as possible. This
+effectually prevents any sticking, should a superfluity of oil happen to
+get on either block or pecker. For similar reasons there should be some
+clearance between A and the pecker, <i>i.e.</i>, the latter should only bear
+at one point and not bed flat against A.</p>
+
+<p>Another form of inertia governor is shown in fig. 26 of the hit and miss
+type, which is employed by Messrs Capel &amp; Co. on many of their engines.</p>
+
+<p>It consists of three main parts&mdash;the brass arm L carried on a stud D, on
+which it is free to move; the weight W, which carries the pecker P
+pivoted at the upper end of L; and the pecker block B, which engages the
+pecker when the engine requires a charge of gas.</p>
+
+<p><span class='pagenum'><a name="Page_57" id="Page_57">[Pg 57]</a></span></p><p>The governing action is dependent upon the shape of the operating cam
+from X to Y. (In the case already dealt with, the lever L serves to
+operate both air and gas valves, and so one cam only is necessary; but
+in this instance the gas valve is operated by a separate cam, and a
+greater nicety of adjustment is obtainable.)</p>
+
+<div class="figright" style="width: 450px;">
+<img src="images/image26.jpg" width="450" height="356" alt="Fig. 26." title="" />
+<span class="caption"><span class="smcap">Fig. 26.</span></span>
+</div>
+
+<p>If the speed of the engine is sufficiently high, the arm L is thrust
+forward at such a rate that the weight W tends to lag behind, with the
+result that P is raised above the notch in B, as shown by the dotted
+lines in drawing. On the other hand, when the speed is too low, the arm
+L will not be thrust forward with so great a degree of suddenness, the<span class='pagenum'><a name="Page_58" id="Page_58">[Pg 58]</a></span>
+weight W will have time to move with L, and the relative position of W
+and P to L will remain the same. Hence, in the first case, when a
+<i>further</i> forward movement is given to L by the cam, the pecker P is
+clear of B, and omits to open the gas valve V; in the second case, P
+engages with B, and the gas valve is held open during the time the
+portion of cam Y to Z is passing over the roller R on arm L.</p>
+
+<p>The great drawback to some forms of governors is not that they fail to
+govern well when new, but that no provision is made to ensure them
+working steadily when a bit worn. The shape of the cam has everything to
+do with the regular working of this form of governor.</p>
+
+<p>Supposing our cam was of the shape shown in fig. 27, <i>i.e.</i>, the
+governing and opening portion all in one curve, it would cause the
+pecker to move both <i>forward</i> and in an <i>upward</i> direction at the <i>same
+time</i>, so that at the moment of engaging B, P might still be moving in
+an upward direction, which would cause uncertainty of action, especially
+if the tips of the engaging members were at all blunt through wear; and,
+in all probability, P would fly off B after partially opening the gas
+valve.</p>
+
+<p>This behaviour is very undesirable, as the small quantity of gas so
+admitted to the cylinder is quite useless, and a sheer waste is
+incurred. With the governing arrangement shown in fig. 26, this trouble
+does not exist. The cam is so designed that the first rise from X to A
+determines whether or not the valve is to be opened; the curve from A to
+Y is<span class='pagenum'><a name="Page_59" id="Page_59">[Pg 59]</a></span> struck from the centre of the side shaft; thus, during that
+portion of the revolution the arm L is stationary, and the pecker at the
+same instant takes up a definite position either in the notch in B or on
+top of it, and is ready to open the valve if the speed of the engine is
+such as to require an explosion, or simply to slide over the top of B,
+allowing the valve to remain closed. It is most interesting to observe
+the action of this governor; when an engine fitted with one is running
+very slowly, the three distinct movements of the pecker P may be clearly
+discerned as the respective portions of the cam pass over the small
+roller R.</p>
+
+<div class="figcenter" style="width: 350px;">
+<img src="images/image27.jpg" width="350" height="352" alt="Fig. 27." title="" />
+<span class="caption"><span class="smcap">Fig. 27.</span></span>
+</div>
+
+
+
+<hr /><p><span class='pagenum'><a name="Page_60" id="Page_60">[Pg 60]</a></span></p>
+<h2><a name="CHAPTER_VII" id="CHAPTER_VII"></a>CHAPTER VII</h2>
+
+<h3>CAMS AND VALVE SETTINGS</h3>
+
+
+<p>With the gas, as with any other kind of engine, the valve settings are
+of primary importance. On very small engines it is often the case that
+only the exhaust valve is operated mechanically.</p>
+
+<p>Again, there are several well-known makes which operate the gas and
+exhaust mechanically while the air valve is opened by suction alone.
+Though opinions differ as to which is the best course to take, there can
+be little doubt that, with all three valves mechanically operated, a
+greater nicety of adjustment is obtainable than would be otherwise
+possible. And provided the working parts are neatly made and finished,
+they will take but little power to drive them; and such loss would be
+compensated by the additional power and efficiency obtained from the
+engine, due to satisfactory and correct adjustment.</p>
+
+<p>In fig. 28 we give a diagram showing the exact positions of the crank
+when the gas, air, and exhaust valves open and close respectively, under
+normal conditions of working. The solid circle represents<span class='pagenum'><a name="Page_61" id="Page_61">[Pg 61]</a></span> the first
+revolution of the crank shaft, starting from the commencement of the
+suction stroke, and the dotted circle the second revolution, during
+which the explosion and exhaust strokes take place; the dotted
+horizontal line shows the position of crank at the back and front dead
+centres.</p>
+
+<p>As a clear conception of why certain things happen under certain
+conditions is most desirable, we will first describe the operation of
+marking off the cams which operate the respective valve levers, and then
+discuss the effect of various "settings" of the valves on the running of
+the engine.</p>
+
+<div class="figleft" style="width: 400px;">
+<img src="images/image28.jpg" width="400" height="280" alt="Fig. 28." title="" />
+<span class="caption"><span class="smcap">Fig. 28.</span></span>
+</div>
+
+<p>Assuming that we are still dealing with the Otto cycle engine, the cam
+or side shaft will revolve at precisely half the speed of the crank
+shaft. This 2 to 1 motion is obtained by means of toothed<span class='pagenum'><a name="Page_62" id="Page_62">[Pg 62]</a></span> wheels, or a
+screw gear. In the former case, where plain or bevel cog-wheels are
+employed, the one fixed on the crank shaft must be exactly half the
+diameter of the one on the side shaft, <i>i.e.</i>, it must have one half the
+number of teeth. On the other hand, if a screw gear is used, the
+relative diameters of the two wheels may vary, but the pitch of the
+teeth on the one must be twice that of the other. These wheels sometimes
+have the teeth or thread formed in the casting, and sometimes they are
+cut after a plain casting has been made. The latter kind are, needless
+to say, better than the former, which often require filing up in order
+to make every tooth alike, and ensure sweet running.</p>
+
+<p>We know already in what positions our crank has to be at the opening and
+closing of the three valves, and with the aid of the diagram, fig. 28,
+we can determine the size of the cams. In fig. 29, S is the side shaft
+to which the cams have to be keyed, R the roller on valve lever, the
+latter being represented by the centre lines LL, as all we require to
+find is the motion this lever will transmit to the valve, the spindle of
+which is shown at V.</p>
+
+<p>Fig. 30 shows diagrammatically the position of crank at the opening and
+closing of the air valve. From this we see that the angle through which
+the crank travels during the time the air valve is open is equal to the
+obtuse angle ABC. Now, as the side shaft S revolves at half the speed of
+crank, it is obvious that the former will travel through only half that
+angle in the same space of time, <i>i.e.</i>,<span class='pagenum'><a name="Page_63" id="Page_63">[Pg 63]</a></span> through an angle equal to ABD.
+We can now transfer this angle on to S, fig. 29, and draw two lines SE,
+SF, cutting a circle GHJ, representing the back of the cam, which latter
+passes in front of the roller R without causing any movement of the
+lever L.</p>
+
+<div class="figcenter" style="width: 450px;">
+<img src="images/image29.jpg" width="450" height="477" alt="Fig. 29." title="" />
+<span class="caption"><span class="smcap">Fig. 29.</span></span>
+</div>
+
+<p><span class='pagenum'><a name="Page_64" id="Page_64">[Pg 64]</a></span></p>
+
+<div class="figleft" style="width: 300px;">
+<img src="images/image30.jpg" width="300" height="292" alt="Fig. 30." title="" />
+<span class="caption"><span class="smcap">Fig. 30.</span></span>
+</div>
+
+<div class="figcenter" style="width: 500px;">
+<img src="images/image31.jpg" width="500" height="506" alt="Fig. 31." title="" />
+<span class="caption"><span class="smcap">Fig. 31.</span></span>
+</div>
+
+<p>It will be seen that by drawing a line forming a tangent to the circle
+GHJ at F and another at E, and producing these, they will meet at point
+K. Consequently, as the side shaft rotates in the direction indicated,
+the lever L will <i>begin</i> to open the valve V when the cam is in the
+position shown in fig. 29, reach a maximum opening at K, and finally
+close when the cam has moved so that point E is now where F was. With a
+cam of this shape, however, a considerable portion of the stroke would
+have passed before the valve was raised any <i>appreciable</i><span class='pagenum'><a name="Page_65" id="Page_65">[Pg 65]</a></span> distance off
+its seat; it would only be fully open for an instant, viz., when K was
+passing over R, and would begin to close again directly.</p>
+
+<p>Moreover, if the engine were running at even a slow speed, the motion
+imparted to lever L would be indefinite; and this, especially if the
+governor is fitted to the air valve lever, as in fig. 25, is very
+undesirable. Therefore, to obtain a definite opening we must set out the
+cam, as shown in fig. 31. In this diagram the roller is shown standing
+clear of the back of cam by about <span class="above">1</span>&#8260;<span class="below">16</span> in. A line MN is then drawn,
+forming a tangent to both roller R and circle GHJ at points F and O
+respectively. This gives us the opening portion of cam. Then from the
+centre S with radius SF describe the arc FE (shown dotted in fig. 31),
+and set off the angle required (ABD, fig. 30), as previously explained.
+Through point E draw a line forming a tangent to circle GHJ, and produce
+it towards P. This line gives us the closing portion of cam. The
+distance W is of course variable, according to the amount of lift we
+give the valve. By comparing these two diagrams it will be seen that in
+both cases the valve will be opened the same length of time, but in
+first case the motion will be indefinite and uncertain. In practice the
+corners are rounded off somewhat, in order to obtain a steady motion;
+and when the air cam is also the governing cam, it is advisable to round
+off the opening face, as indicated in fig. 32. Upon the shape of this
+face both the sensitiveness and the life of the governor gear depends.
+If it<span class='pagenum'><a name="Page_66" id="Page_66">[Pg 66]</a></span> is nicely rounded off, giving a gradual rise, very little tension
+(or compression, as the case may be) of the controlling spring will be
+necessary to give the required speed to engine; whereas, if the rise is
+sudden, the spring will have to be screwed up tighter, and, if uneven
+and lumpy (<i>i.e.</i>, not a fair curve), the result will, of course, be
+erratic governing.</p>
+
+<div class="figcenter" style="width: 450px;">
+<img src="images/image32.jpg" width="450" height="484" alt="Fig. 32." title="" />
+<span class="caption"><span class="smcap">Fig. 32.</span></span>
+</div>
+
+<p>A certain amount of clearance should always be provided between the
+roller and the back of cam<span class='pagenum'><a name="Page_67" id="Page_67">[Pg 67]</a></span> (compare figs. 29 and 31), that is, the
+roller should not bear against the cam, except during that portion of
+the stroke in which it is actually operating the valve, viz., from F to
+E (fig. 31). A small stop interposed between the lever and some
+convenient part of the engine, such as the side-shaft bracket bearing,
+answers this purpose.</p>
+
+<div class="figleft" style="width: 300px;">
+<img src="images/image33.jpg" width="300" height="336" alt="Fig. 33." title="" />
+<span class="caption"><span class="smcap">Fig. 33.</span></span>
+</div>
+
+<div class="figcenter" style="width: 450px;">
+<img src="images/image34.jpg" width="450" height="364" alt="Fig. 34." title="" />
+<span class="caption"><span class="smcap">Fig. 34.</span></span>
+</div>
+
+<p>The size and shape of the exhaust cam is found in the same manner as
+above described; the angle through which it operates is greater than
+that of the air cam, and is shown in fig. 33. A fair margin should be
+allowed for filing or machining these castings up; the shape and sizes
+arrived at by the above described method being finished measurements.<span class='pagenum'><a name="Page_68" id="Page_68">[Pg 68]</a></span>
+Fig. 34 gives the outline of an exhaust cam worked out from the setting
+diagram, fig. 33.</p>
+
+<div class="figleft" style="width: 400px;">
+<img src="images/image35.jpg" width="400" height="109" alt="Fig. 35." title="" />
+<span class="caption"><span class="smcap">Fig. 35.</span></span>
+</div>
+
+<div class="figright" style="width: 400px;">
+<img src="images/image37.jpg" width="400" height="109" alt="Fig. 37." title="" />
+<span class="caption"><span class="smcap">Fig. 37.</span></span>
+</div>
+
+<div class="figleft" style="width: 400px;">
+<img src="images/image41.jpg" width="400" height="109" alt="Fig. 41." title="" />
+<span class="caption"><span class="smcap">Fig. 41.</span></span>
+</div>
+
+<div class="figcenter" style="width: 400px;">
+<img src="images/image42.jpg" width="400" height="109" alt="Fig. 42." title="" />
+<span class="caption"><span class="smcap">Fig. 42.</span></span>
+</div>
+
+<p>We may now consider the relative positions these two cams will occupy
+when keyed up on the side shaft. Assuming that we have both cams
+finished to the proper shape and size, and the keyway cut in the side
+shaft, we can commence to mark off the position of keyway in the air
+cam. With the crank in the position shown in fig. 35, the air cam is<span class='pagenum'><a name="Page_69" id="Page_69">[Pg 69]</a></span>
+slipped on to the side shaft and brought to the position shown in fig.
+32. The keyway being already cut in the side shaft, the position for
+that in the cam may be scribed off, as shown by dotted lines (fig. 32),
+the cam removed, and the keyway cut. It is as well, however, to check
+this mark by turning the crank round to position shown in fig. 37,
+<i>i.e.</i>, the closing of air valve. The side shaft will also turn through
+exactly half this angle, so that when the cam is again slipped on the
+latter, the scriber marks and keyway in shaft should be exactly in line,
+as they were in fig. 32, and the fall of the cam&mdash;the closing
+portion&mdash;should just be touching roller R, but not sufficient to keep
+the valve open (see fig. 38). The slightest movement of the crank from
+this point in a forward direction should result in a little play<span class='pagenum'><a name="Page_70" id="Page_70">[Pg 70]</a></span> being
+felt in the lever L, assuming that the cam is also moved just enough to
+keep the scriber marks in line with the existing keyway.</p>
+
+<div class="figcenter" style="width: 450px;">
+<img src="images/image36.jpg" width="450" height="328" alt="Fig. 36." title="" />
+<span class="caption"><span class="smcap">Fig. 36.</span></span>
+</div>
+
+<div class="figcenter" style="width: 400px;">
+<img src="images/image38.jpg" width="400" height="435" alt="Fig. 38." title="" />
+<span class="caption"><span class="smcap">Fig. 38.</span></span>
+</div>
+
+<div class="figcenter" style="width: 400px;">
+<img src="images/image39.jpg" width="400" height="435" alt="Fig. 39." title="" />
+<span class="caption"><span class="smcap">Fig. 39.</span></span>
+</div>
+
+<p>By these operations it will be at once evident whether the cam is too
+large or too small. Supposing it is too small, we will obtain two sets
+of marks indicating the position of keyway, as shown in fig. 39, and it
+is obvious that we must give the lever less play by screwing up the set
+screws shown in fig. 11. The effect of this is to cause the valve to
+open earlier and close later than it would if the play were greater; as
+it would were the operating portion of cam larger. A minimum amount of
+play must always be allowed, however. When two sets of marks are
+obtained, the mean must be taken and the keyway cut as shown by the
+thick lines in fig.<span class='pagenum'><a name="Page_71" id="Page_71">[Pg 71]</a></span> 39. The exhaust cam in larger engines is usually
+made with a swelling on the opening portion, as shown in fig. 40, so
+that the valve is <i>very slightly</i> opened some time before the crank has
+reached the position shown in fig. 41. Fig. 42 shows position of crank
+at the close of exhaust valve, and the two last-mentioned diagrams
+correspond with the two positions in which the exhaust cam is shown in
+fig. 34. The small lump on the back of exhaust cam, fig. 40, is only
+required on engines above 3 B.H.P. to relieve the compression on the
+compression stroke when starting up. By moving the roller R on valve
+lever longitudinally, so that it engages both parts of cam as they pass
+in front of it, the exhaust valve is held open during a small portion of
+the compression stroke, usually closing when the crank has reached the
+bottom centre.</p>
+
+<p>Referring again to fig. 26, this gas or governor cam may be set out, and
+the keyway marked on the same principle as already described for the air
+and exhaust valves. An end view of the three cams keyed up on the side
+shaft is given in fig. 40<span class="smcap">A</span>. In small engines it is convenient to have
+the air and exhaust cams made in one casting, when one key only will be
+required. On some engines, instead of employing a movable roller or
+valve lever, the exhaust cam is fitted on side shaft with a
+"feather"&mdash;<i>i.e.</i>, a headless key&mdash;and the cam being capable of
+longitudinal movement, such movement being controlled by a small lever
+or handle, called the half-compression lever.</p>
+
+<p><span class='pagenum'><a name="Page_72" id="Page_72">[Pg 72]</a></span></p>
+
+<div class="figleft" style="width: 300px;">
+<img src="images/image40.jpg" width="300" height="264" alt="Fig. 40" title="" />
+<span class="caption"><span class="smcap">Fig. 40</span></span>
+</div>
+
+<div class="figright" style="width: 450px;">
+<img src="images/image40a.jpg" width="450" height="392" alt="Fig. 40a" title="" />
+<span class="caption"><span class="smcap">Fig. 40a</span></span>
+</div>
+
+<p>Having once thoroughly grasped the important part the cams play in the
+working of the engine, it will be an easy matter to adjust the valve
+settings, and to keep them adjusted correctly. The effect of a wrong
+setting will then be strikingly apparent. On small engines a separate
+cam to operate the gas valve is not a necessity; and the practice of
+fitting<span class='pagenum'><a name="Page_73" id="Page_73">[Pg 73]</a></span> the gas valve spindle (or the pecker, the effect would be the
+same) with a device for increasing or diminishing its length, is also
+unnecessary and unsound.</p>
+
+<p>The wear on a well-designed gas valve operating mechanism is practically
+nil; and even if there was wear, the effect would be to cause the valve
+to open a trifle later and close sooner than it would otherwise, <i>i.e.</i>,
+it would remain open a shorter time during each charging stroke. This in
+turn (other conditions remaining the same) would give us a weaker
+mixture; and although too weak a mixture is preferable to a too rich
+one, we should have to adopt some means of increasing the richness of
+the mixture; otherwise the maximum power of the engine would soon be
+seen to diminish.</p>
+
+<p>To get the mixture normal again we must either enlarge the gas inlet or
+cut down the air-supply somewhat, and so keep the proportions the same.
+That is to say, the quality of the mixture is dependent upon the
+relative dimension of the gas and air inlets. We know by actual trial
+that if at the completion of the charging stroke the pressure in the
+cylinder is approximately that of the atmosphere, better results are
+obtained than when the pressure is considerably below that of the
+atmosphere. Thus, the larger we make the inlet ports (but still
+retaining correct relative dimensions) the more readily will the mixture
+be drawn into the cylinder as the piston moves forward, tending to
+create a vacuum. Of the two courses open to us to retain a good mixture
+it is preferable to open out the gas-supply, for by cutting<span class='pagenum'><a name="Page_74" id="Page_74">[Pg 74]</a></span> down the
+air-supply, and sucking the gas in, due to the partial vacuum being
+formed, we should be keeping the proportions correct at the expense of
+reducing the total volume of the explosive mixture (more strictly
+speaking, the density of the charge) admitted to the cylinder.</p>
+
+<p>Under normal conditions it is not necessary to create a high vacuum to
+suck the gas into the cylinder, but it is as well to understand what
+results we would tend to produce, did we work on these lines. Of course,
+with small high-speed engines fitted with suction air valve, the vacuum
+is higher than it would be in slow-speed engines with mechanically
+operated valves. If we take an extreme case as an example, where, to get
+any gas to speak of into the cylinder the air-supply would have to be
+cut down or throttled to an abnormal extent, we will realise at once
+that such a small quantity of both air and gas would have been drawn in,
+and consequently the mixture would be so rarefied that on the
+compression stroke the pressure would possibly be extremely low and
+totally inadequate to produce efficient working. Moreover, working at
+such a high vacuum as this would not only prevent us obtaining a normal
+explosion in the cylinder, but would upset the working of the exhaust
+valve. The latter being held down on its seat during the suction stroke
+by means of a spiral spring would be lifted off its seat by suction (the
+partial vacuum in the cylinder), and any burnt gases which happened to
+be hanging about in the exhaust port or pipe would be drawn into the<span class='pagenum'><a name="Page_75" id="Page_75">[Pg 75]</a></span>
+cylinder again, and tend to damp the ensuing explosion. Too early
+closing of the exhaust should be avoided almost as rigorously as too
+late. The latter will affect the working in a similar way to the exhaust
+being lifted on the charging stroke by suction; on the other hand, if it
+closes too soon, the entire volume of burnt gases will not have been
+swept out of the cylinder, and the effect will again be to damp the
+following explosion.</p>
+
+<p>The gas valve opens just after the crank is above the back centre and
+closes just before the front centre is reached, that is, opening a
+little after the air valve and closing a shade before it, thus every
+particle of gas is used in the cylinder, due to a draught of air being
+drawn in after the gas valve has been closed.</p>
+
+<p>The settings of the valve being of primary importance, no matter what
+size engine we are dealing with, and being also the most confusing
+matter for anyone unacquainted with gas engines to grasp, it will not be
+out of place to suggest a simple method of checking these settings.</p>
+
+<p>Let us begin by pulling the fly-wheel round backwards until we feel the
+piston is on the compression stroke, then from this point&mdash;the crank
+being about 45&deg; above the front centre&mdash;pull the wheel round until the
+crank is in the position for the exhaust opening (see fig. 28). In this
+position there should be but the <i>slightest</i> play in the exhaust lever,
+showing that the valve is <i>just</i> on point of opening; and by keeping
+one's hand on the lever whilst the fly-wheel<span class='pagenum'><a name="Page_76" id="Page_76">[Pg 76]</a></span> is pulled round <i>very
+slowly</i> (it is a good plan to get some one else to do the pulling
+round), it is possible to ascertain the precise point at which the valve
+opens. Next pull round till the crank is in the position for the air
+valve opening, and observe that it is set correctly. Then go on to a
+trifle above the back centre, where the exhaust valve should close, and
+so on till the opening and closing of each valve has been checked. It
+will be noticed that the air, and sometimes the gas, valve opens before
+the exhaust closes. This overlap is necessary; and it will be found that
+the smaller the engine and the higher the speed the greater this overlap
+will be to obtain good results, although a good deal of individual
+judgment must be used in settling the exact amount of overlap, as the
+requisite amount may, to get the best results, vary in different engines
+of precisely the same dimensions and type.</p>
+
+<p>When dealing with engines which have no separate gas valve&mdash;the gas
+being admitted with the air, which is sometimes the case with very small
+engines&mdash;the above notes referring to the gas setting independently,
+will, of course, not hold good.</p>
+
+<p>It may be mentioned with regard to the lump on the opening side of the
+exhaust cam, that this if overdone is found to be detrimental on large
+engines, and even on small ones. If it is too large, it will cause both
+exhaust valve and seat to become burnt and pitted, due to the surface
+being exposed to the exceedingly high temperature of the expanding
+gases. If it is too large, it is equivalent to opening the exhaust valve
+too early, and the effect is the same, viz., a waste of power and damage
+to the valve and its seat.</p>
+
+<p><span class='pagenum'><a name="Page_77" id="Page_77">[Pg 77]</a></span></p>
+<div class="figcenter" style="width: 350px;">
+<img src="images/image43.jpg" width="350" height="651" alt="Fig. 43." title="" />
+<span class="caption"><span class="smcap">Fig. 43.</span></span>
+</div>
+
+<p><span class='pagenum'><a name="Page_78" id="Page_78">[Pg 78]</a></span></p>
+<div class="figcenter" style="width: 450px;">
+<img src="images/image44.jpg" width="450" height="231" alt="Fig. 44.&mdash;Brake Testing." title="" />
+<span class="caption"><span class="smcap">Fig. 44.</span>&mdash;Brake Testing.</span>
+</div>
+
+<p>The method of grinding in the valves to their seats with emery powder
+and oil is so well known that no further description is needed here. We
+give, however, in fig. 43 a sketch showing a very expeditious way of
+dealing with very badly worn or burnt seats. The sketch explains itself.
+Such a tool is readily made; even the cutter could be turned and filed
+up to shape and then hardened at home. By lightly tapping in the taper
+cotter pin little by little, sufficient pressure is put on the cutter to
+make it an easy matter to completely re-face an old seat or form a new
+one. A T-wrench or "tommy" can be used to work the cutter spindle. The
+lower part of the latter must be the same diameter as the existing valve
+spindle; the bush acts as a guide; and as the bevel of the cutter<span class='pagenum'><a name="Page_79" id="Page_79">[Pg 79]</a></span>
+should be the same as that of the valve, a very little grinding in with
+emery powder is required to finish the job off.</p>
+
+<p>In fig. 44 we give a diagram showing the method of testing for Brake
+H.P. of engine, as it is frequently interesting to make such a simple
+test after any alterations or adjustments have been made.</p>
+
+<p>Two spring balances and a rope or cord (according to the size of the
+engine), fitted with a few wood blocks as shown in section, fig. 44, to
+keep the rope on the rim of fly-wheel, is all that is required for this
+test. The following formula may be used for arriving at the B.H.P.:&mdash;</p>
+
+<p class="center">
+B.H.P. = (S<sub>1</sub> &#8722; S<sub>2</sub>) 3ˇ14 &times; D x R / 33000<br />
+<br /></p>
+<p>S<sub>1</sub> = Reading in lbs. of spring balance No. 1.</p>
+<p>S<sub>2</sub> = Reading in lbs. of spring balance No. 2.</p>
+<p>D = Diameter of fly-wheel and diameter of brake rope in feet.</p>
+<p>R = Revolutions of fly-wheel per minute.</p>
+
+<p>As 3ˇ14 &times; D / 33000 will always remain the same for any given engine and
+gear, we may call that expression C; then the B.H.P. may be written&mdash;</p>
+
+<p class="center">
+B.H.P. = (S<sub>1</sub> &#8722; S<sub>2</sub>) C R.<br />
+</p>
+
+
+
+<hr /><p><span class='pagenum'><a name="Page_80" id="Page_80">[Pg 80]</a></span></p>
+<h2><a name="CHAPTER_VIII" id="CHAPTER_VIII"></a>CHAPTER VIII</h2>
+
+<h3>OIL ENGINES</h3>
+
+
+<p>The small oil engine is practically the same as the gas engine, with the
+addition of a vaporiser for converting the oil into gas, or vapour, to
+be exploded in the cylinder; consequently the one may be converted into
+the other in many cases without much trouble. The difficulty of
+producing an efficient oil engine lies principally in devising a
+satisfactory and reliable vapouriser&mdash;one which will work equally well
+under all loads. The heat supplied to the chamber must be sufficient to
+vaporise the oil, but not great enough to decompose it. There are
+various methods of vaporising the oil, and many types of vaporisers are
+employed to attain the same end. There are some in which a charge of oil
+is drawn by suction into a hot chamber in which it is converted into
+vapour and at the same time mixed with a small quantity of hot air; this
+rich mixture is then passed into the combustion chamber of the engine,
+in the same manner as coal-gas would be, where it is further diluted
+with more<span class='pagenum'><a name="Page_81" id="Page_81">[Pg 81]</a></span> air drawn in through the air valve. Other arrangements cause
+a jet of oil to be injected into a chamber containing hot air, in the
+form of spray, which immediately converts the oil into vapour, and is
+then passed into the cylinder, compressed, and fired. Then, again, we
+can pump oil through a spraying nipple into the vapouriser (which is
+kept at a suitable temperature) whilst the cylinder is being filled with
+air on the suction stroke. On the following compression stroke the air
+is driven into the vapouriser, which communicates with the cylinder
+through a narrow neck, and mixes intimately with the oil vapour.
+Gradually, as the pressure rises, due to compression, the charge becomes
+more and more explosive, until at the completion of this stroke it has
+attained the proper proportions of air and oil vapour, and is fired by
+the temperature of the vapouriser and that caused by a high compression;
+that is, the charge is fired automatically; and once the engine is
+running, no heating lamp is required to keep the vapouriser at the
+correct temperature. It is necessary, however, to raise it to the
+workable temperature at starting. This is known as the Hornsby-Akroyd
+method.</p>
+
+<p>Capel's arrangement is also simple and efficient, and has the additional
+advantage of being capable of being fitted to their existing gas
+engines, the conversion being made in a very short time. This vapouriser
+consists primarily of a tubular casting A, on the outside of which are
+formed a series of vertical ribs, shown in plan, fig. 46, running<span class='pagenum'><a name="Page_82" id="Page_82">[Pg 82]</a></span> to
+within a short distance of the flange at one end, as shown in the
+section, fig. 45, thus providing an annular space C between the upper
+ends of the ribs and the flange. This casting is enclosed by an outer<span class='pagenum'><a name="Page_83" id="Page_83">[Pg 83]</a></span>
+casing B, which fits well over the inner tube. It has also a number of
+small holes drilled near the lower end communicating with the channels
+between the ribs. Thus it will be seen that when the gas valve is opened
+and suction takes place, air is drawn in through these holes, passes up
+into the annular space C below the top flange, from there travels to the
+opposite side of vapouriser, and mixes with the oil which is also being
+drawn in through a small nipper at N, fig. 45. Both then pass between a
+series of pegs, where they become thoroughly mixed, and finally pass on
+to the inlet valve V, fig. 47, and so into the cylinder, where the
+complete charge is mixed up and compressed and fired in the usual
+manner. Iron ignition tubes may be used, and one heating lamp serves a
+double purpose in keeping the tube and vapouriser hot at the same time.
+This lamp is fed by means of a pump actuated from the side shaft. The
+plunger of the pump is loaded with a spiral spring, which may be
+adjusted to give any desired pressure, and is kept constant and steady
+by means of an air vessel. This pump is shown in fig. 48. It is actuated
+by means of a rod and lever from the side shaft of engine. The plunger P
+works in a barrel B, which is carried by a small reservoir R, the latter
+being in communication with the main oil tank by means of the pipe H.</p>
+
+<div class="figleft" style="width: 300px;">
+<img src="images/image46.jpg" width="300" height="276" alt="Fig. 46." title="" />
+<span class="caption"><span class="smcap">Fig. 46.</span></span>
+</div>
+
+<div class="figright" style="width: 450px;">
+<img src="images/image45.jpg" width="450" height="537" alt="Fig. 45." title="" />
+<span class="caption"><span class="smcap">Fig. 45.</span></span>
+</div>
+
+<p><span class='pagenum'><a name="Page_84" id="Page_84">[Pg 84]</a></span></p>
+<div class="figleft" style="width: 350px;">
+<img src="images/image47.jpg" width="350" height="749" alt="Fig. 47." title="" />
+<span class="caption"><span class="smcap">Fig. 47.</span></span>
+</div>
+
+<p><span class='pagenum'><a name="Page_85" id="Page_85">[Pg 85]</a></span></p>
+<div class="figright" style="width: 350px;">
+<img src="images/image48.jpg" width="350" height="392" alt="Fig. 48." title="" />
+<span class="caption"><span class="smcap">Fig. 48.</span></span>
+</div>
+
+<div class="figleft" style="width: 400px;">
+<img src="images/image49.jpg" width="400" height="653" alt="Fig. 49." title="" />
+<span class="caption"><span class="smcap">Fig. 49.</span></span>
+</div>
+
+<p><span class='pagenum'><a name="Page_86" id="Page_86">[Pg 86]</a></span></p>
+<div class="figright" style="width: 350px;">
+<img src="images/image50.jpg" width="350" height="464" alt="Fig. 50." title="" />
+<span class="caption"><span class="smcap">Fig. 50.</span></span>
+</div>
+
+<div class="figcenter" style="width: 450px;">
+<img src="images/image51.jpg" width="450" height="497" alt="Fig 51." title="" />
+<span class="caption"><span class="smcap">Fig. 51.</span></span>
+</div>
+
+<p>The plunger is loaded with a spiral spring, and has a ball valve, as
+shown. Intermediate between this small reservoir and the main oil tank
+is another set of valves, shown in fig. 49. It will be seen that the
+suction of the pump will draw the oil up, the small and lower ball
+valve, of course, allowing it to pass freely. On the down stroke the
+lower valve will be automatically closed, and the oil will be put under
+pressure, this being determined by the load on the plunger valve, which
+is adjustable by means of the screw S, fig. 48. When the required
+pressure in<span class='pagenum'><a name="Page_87" id="Page_87">[Pg 87]</a></span> the pipe P, figs. 45 and 49, has been attained, the plunger
+valve lifts on each stroke and the surplus oil flows through the plunger
+into the small reservoir R. The latter is at about the same level as
+another still smaller reservoir M (shown in figs. 47 and 50), a flow of
+oil being established between the two by means of a pipe Q (see figs. 48
+and 50). In the reservoir R is fitted an overflow pipe, so that the oil
+cannot rise beyond a certain level; hence the head of oil in the smaller
+one M is always constant. On the suction stroke a partial vacuum is
+formed in the engine cylinder, consequently the pressure in the
+vapouriser drops somewhat below that of the atmosphere,<span class='pagenum'><a name="Page_88" id="Page_88">[Pg 88]</a></span> and this small
+difference in pressure is enough to cause the oil to rise in the small
+passage X, fig. 45, beyond its normal level, and overflow into the
+vapourising chamber, as previously described. The valve or nipper N is
+shown open in the diagram, fig. 45, and all that is required to stop the
+engine when running is to drop the small handle L, fig. 45, when the
+valve will close, due to the spring S. The air vessel shown in fig. 49
+is in communication with the pipe leading to the blow lamp. A pressure
+gauge can also be fitted, although it is not in any way a necessity.</p>
+
+<p>The ratchet wheel and pawl shown in fig. 48 are part of the lubricator.
+The wheel drives a brass or gun-metal plug, producing an intermittent
+rotary motion. The plug has a small hole in its periphery, which becomes
+filled with oil when it is at the upper part of its travel, and empties
+the oil out into a discharge pipe T, when it is inverted, and is then
+led away and applied to the piston at the required spot. Fig. 51 shows
+this arrangement in section.</p>
+
+
+
+
+
+
+
+
+<pre>
+
+
+
+
+
+End of the Project Gutenberg EBook of Gas and Oil Engines, Simply Explained, by 
+Walter C. Runciman
+
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+</body>
+</html>
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@@ -0,0 +1,1969 @@
+The Project Gutenberg EBook of Gas and Oil Engines, Simply Explained, by
+Walter C. Runciman
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+
+Title: Gas and Oil Engines, Simply Explained
+       An Elementary Instruction Book for Amateurs and Engine Attendants
+
+Author: Walter C. Runciman
+
+Release Date: November 17, 2008 [EBook #27286]
+
+Language: English
+
+Character set encoding: ASCII
+
+*** START OF THIS PROJECT GUTENBERG EBOOK GAS AND OIL ENGINES ***
+
+
+
+
+Produced by Steven Gibbs, Greg Bergquist and the Online
+Distributed Proofreading Team at https://www.pgdp.net
+
+
+
+
+
+
+
+
+
+
+
+  GAS AND OIL ENGINES
+
+  SIMPLY EXPLAINED
+
+  _An Elementary Instruction Book for Amateurs
+  and Engine Attendants_
+
+
+  BY
+  WALTER C. RUNCIMAN
+
+
+  _FULLY ILLUSTRATED_
+
+
+  LONDON
+
+  Model Engineer Series. The "Model Engineer"
+  Series, no. 26.
+
+  1905
+
+
+
+
+CONTENTS
+
+  CHAP.                                                PAGE
+
+        PREFACE                                           5
+
+
+     I. INTRODUCTORY                                      7
+
+    II. THE COMPONENT PARTS OF AN ENGINE                 13
+
+   III. HOW A GAS ENGINE WORKS                           22
+
+    IV. IGNITION DEVICES                                 33
+
+     V. MAGNETO IGNITION                                 47
+
+    VI. GOVERNING                                        51
+
+   VII. CAMS AND VALVE SETTINGS                          63
+
+  VIII. OIL ENGINES                                      81
+
+
+
+
+PREFACE
+
+
+My object in placing this handbook before the reader is to provide him
+with a simple and straightforward explanation of how and why a gas
+engine, or an oil engine, works. The main features and peculiarities in
+the construction of these engines are described, while the methods and
+precautions necessary to arrive at desirable results are detailed as
+fully as the limited space permits. I have aimed at supplying just that
+information which my experience shows is most needed by the user and by
+the amateur builder of small power engines. In place of giving a mere
+list of common engine troubles and their remedies, I have thought it
+better to endeavour to explain thoroughly the fundamental principles and
+essentials of good running, so that should any difficulty arise, the
+engine attendant will be able to reason out for himself the cause of the
+trouble, and will thus know the proper remedy to apply. This will give
+him a command over his engine which should render him equal to any
+emergency.
+
+  WALTER C. RUNCIMAN.
+
+  LONDON, E.C.
+
+
+
+
+GAS AND OIL ENGINES
+
+SIMPLY EXPLAINED
+
+
+
+
+CHAPTER I
+
+INTRODUCTORY
+
+
+The history of the gas engine goes back a long way, and the history of
+the internal combustion engine proper further still. It will be
+interesting to recount the main points in the history of the development
+of the class of engine we shall deal with in the following pages, in
+order to show what huge strides were made soon after the correct and
+most workable theory had been formulated.
+
+In 1678 Abbe Hautefeuille explained how a machine could be constructed
+to work with gunpowder as fuel. His arrangement was to explode the
+gunpowder in a closed vessel provided with valves, and cool the products
+of combustion, and so cause a partial vacuum to be formed. By the aid of
+such a machine, water could be raised. This inventor, however, does not
+seem to have carried out any experiments.
+
+In 1685 Huyghens designed another powder machine; and Papin, in 1688,
+described a similar machine, which was provided with regular valves, as
+devised by himself, in the _Proceedings of the Leipsic Academy_, 1688.
+From this time until 1791, when John Barber took out a patent for the
+production of force by the combustion of hydrocarbon in air, practically
+no advancement was made. The latter patent, curiously enough, comprised
+a very primitive form of rotary engine. Barber proposed to turn coal,
+oil, or other combustible stuff into gas by means of external firing,
+and then to mix the gases so produced with air in a vessel called the
+exploder. This mixture was then ignited as it issued from the vessel,
+and the ensuing flash caused a paddle-wheel to rotate. Mention is also
+made that it was an object to inject a little water into the exploder,
+in order to strengthen the force of the flash.
+
+Robert Street's patent of 1794 mentions a piston engine, in the cylinder
+of which, coal tar, spirit, or turpentine was vaporised, the gases being
+ignited by a light burning outside the cylinder. The piston in this
+engine was thrown upwards, this in turn forcing a pump piston down which
+did work in raising water. This was the first real gas engine, though it
+was crude and very imperfectly arranged.
+
+In 1801 Franzose Lebon described a machine to be driven by means of
+coal-gas. Two pumps were used to compress air and gas, and the mixture
+was fired, as recommended by the inventor, by an electric spark, and
+drove a piston in a double-working cylinder.
+
+The atmospheric engine of Samuel Brown, 1823, had a piston working in a
+cylinder into which gas was introduced, and the latter, being ignited,
+expanded the air in cylinder whilst burning like a flame. The fly-wheel
+carried the piston up to the top of its stroke, then water was used to
+cool the burnt gases, which also escaped through valves, the latter
+closing when the piston had reached the top of its stroke. A partial
+vacuum was formed, and the atmospheric pressure did work on the piston
+on its down stroke. A number of cylinders were required in this engine,
+three being shown in the specification all connected to the same
+crank-shaft. According to the _Mechanic's Magazine_, such an engine with
+a complete gas generating plant was fitted to a boat which ran as an
+experiment upon the Thames.
+
+A two-cylinder engine working on to a beam was built in Paris, but no
+useful results were obtained.
+
+Wright's engine of 1833 used a mixture of combustible gas and air, which
+operated like steam in a steam engine. This engine had a water-jacket,
+centrifugal governor, and flame ignition. In 1838 Barnett applied the
+principle of compression to a single-acting engine. He also employed a
+gas and air pump, which were placed respectively on either side of the
+engine cylinder, communication being established between the receiver
+into which the pumps delivered and the working cylinder as the charge
+was fired. The double-acting engines which Barnett devised later were
+not so successful.
+
+From this time to about 1860 very few practical developments are
+recorded. A number of French and English patents were taken out,
+referring to hydrogen motors, but are not of much practical value.
+
+Lenoir's patent, dating from 24th January 1860, refers to a form of
+engine which received considerable commercial support, and consequently
+became very popular. A manufacturer, named Marinoni, built several of
+these engines, which were set to work in Paris in a short time. Then,
+due to sudden demand, the Lenoir Company was formed to undertake the
+manufacture of these engines. It was claimed that a 4-horse-power engine
+could be run at a cost of 3.4 shillings per day, or just one half the
+cost of a steam engine using 9.9 pounds of coal per horse-power per
+hour. Many similar exaggerated accounts of their economy in consumption
+were circulated, and the public, on the strength of these figures,
+bought.
+
+It was understood that 17.6 cubic ft. of gas were required per
+horse-power per hour, but it was found that as much as 105 cubic ft.
+were often consumed. The discrepancy between the stated figures and the
+actual performance of the engine was a disappointment to the using
+public, and, as a result, the Lenoir engine got a bad name.
+
+Hugon, director of the Parisian gas-works, who, together with Reithmann,
+a watchmaker of Muenich, hotly contested Lenoir's priority to this
+invention, brought out a modification of this engine. He cooled the
+cylinder by injecting water as well as using a water-jacket, and used
+flame instead of electric ignition. The consumption was now brought down
+to 87.5 cubic ft.
+
+At the second Parisian International Exhibition, 1867, an atmospheric
+engine, invented by Otto & Langen about this time, was shown. In this
+engine a free piston was used in a vertical cylinder, the former being
+thrown up by the force of the explosion. The only work done on the
+up-stroke was that to overcome the weight of the piston and piston rod,
+and the latter being made in the form of a rack, engaged with a toothed
+wheel on the axle as the piston descended, causing the fly-wheel and
+pulley to rotate.
+
+Barsanti and Matteucci were engaged in devising and experimenting with
+an engine very similar to this some years before, but Otto & Langen, no
+doubt, worked quite independently. Barsanti's engine never became a
+commercial article; while Otto & Langen's firm, it is said, held their
+own for ten years, and turned out about 4000 engines. In 1862 the French
+engineer, Beau de Rochas, laid down the necessary conditions which must
+prevail in order to obtain maximum efficiency. His patent says there are
+four conditions for perfectly utilising the force of expansion of gas in
+an engine.
+
+(1) Largest possible cylinder volume contained by a minimum of surface.
+
+(2) The highest possible speed of working.
+
+(3) Maximum expansion.
+
+(4) Maximum pressure at beginning of expansion.
+
+These are the conditions and principles, briefly stated, that combine to
+form the now well-known cycle upon which most gas engines work at the
+present time.
+
+It was not until 1876, fifteen years after these principles had been
+enumerated, that Otto carried them into practical effect when he brought
+out a new type of engine, with compression before ignition, higher
+piston speed, more rapid expansion, and a general reduction of
+dimensions for a given power. Due to this achievement, the cycle above
+referred to has always been termed the "Otto" cycle.
+
+
+
+
+CHAPTER II
+
+THE COMPONENT PARTS OF AN ENGINE
+
+
+Having recounted very briefly the chief points in the development of the
+gas engine from its beginning, we may proceed to deal with matters of
+perhaps more practical interest to those who we are assuming have had
+little or no actual experience in making or working internal combustion
+engines.
+
+The modern gas engine comprises comparatively few parts. Apart from the
+two main castings--the bed and cylinder--a small engine, generally
+speaking, consists of four fundamental members, viz., the valves and
+their operating mechanism, the cams and levers; the ignition device for
+firing the charge; and the governing mechanism for regulating the supply
+and admission of the explosive charge. There are innumerable designs of
+each one of these parts, and no two makes are precisely alike in detail,
+as every maker employs his own method of achieving the same end, namely,
+the production of an engine which comprises maximum efficiency with a
+minimum of wear and tear and attention.
+
+Therefore, before dealing with each of these primary parts in an
+arbitrary manner, and with the cycle of operations in detail, we propose
+to make the reader familiar with the general arrangement and method of
+working which usually obtains in the smaller power engines. In the
+following illustrations these parts are shown. A (fig. 1) is the
+ignition device which carries the ignition tube to fire the charge. H
+and I (fig. 2) are the main valves, and GC (fig. 1.) is the gas-cock.
+The side or cam shaft N (sometimes called the 2 to 1 shaft), the cams
+which move the levers M, the latter in turn operating the valves, and
+causing them to open and close at the proper time, are shown in fig. 11.
+A bracket bolted up to the side of cylinder forms a bearing for one end
+of the side shaft, and also carries a spindle at its lower end on which
+the levers oscillate, transmitting the motion imparted to them by the
+cams to the valves. The main cylinder casting and the bed need no
+description. In some cases the bed is in two portions, though now a
+great many makers are discarding the lower portion altogether, having
+found that it is cheaper, and quite as satisfactory, to use a built-up
+foundation instead, and, if necessary, to cut a trough for the fly-wheel
+to run it. This arrangement, however, only obtains where larger engines
+are concerned. A half-compression handle by which the exhaust cam is
+moved laterally on the side shaft as required is not needed on very
+small engines.
+
+[Illustration: FIG. 1.--General Arrangement of a Gas Engine and
+Accessories.]
+
+Further reference will be made to this in another chapter, and,
+although this is not a necessity on a _small_ engine, it is always
+employed on engines over 2 B.H.P. In fig. 1, HW is the cooling water
+outlet and CW the inlet. A small drain cock is shown at DC, through
+which the water in the cylinder water-jacket may be drawn off when
+required. The pipes leading to the inlet and outlet of this supply are
+connected to the cooling water tank by means of a couple of broad, flat
+nuts and lead washers, one inside and the other outside the tank, the
+latter, when clamped up well, making a perfectly water-tight joint. The
+outlet pipe making an acute angle with the side of tank, the washers
+used there should be wedge-shape in section. It is also desirable to fit
+a stop-cock SC, so that the pipes can be disconnected from the engine
+entirely, or the water-jacket emptied without running the whole of the
+water out of the tank. The exhaust pipe EP is made up of gas-barrel. It
+should lead from the engine to the silencer or exhaust box (if one is
+found to be necessary) as directly as possible, _i.e._, with no more
+bends than are needed, and what there are should not be acute. The
+silencer can be inside or outside the engine-room, whichever is most
+convenient; but both it and the exhaust piping should be kept from all
+direct contact with wood-work, and at the same time in a readily
+accessible position.
+
+Beyond the exhaust-pipe and box and the water-tank, the gas bag GB and
+gas meter (where small powers are concerned, the ordinary house or
+workshop lighting meter may be used without inconvenience) are the only
+other accessories which are included in a small installation.
+
+[Illustration: FIG. 2.--A Section of a Gas Engine.]
+
+Fig. 2 gives a sectional view, showing the cylinder and liner. The
+latter is a very desirable feature in any type of gas engine, but
+especially in the larger sizes; for at any future time, should it be
+found necessary to re-bore the liner, it can be removed with comparative
+ease, and is, moreover, more readily dealt with in the lathe than the
+whole cylinder casting would be.
+
+The liner is virtually a cast-iron tube, with a specially shaped flange
+at either end. At the back end the joint between it and the cylinder
+casting has to be very carefully made. This is a water _and_ explosion
+joint; hence it has not only to prevent water entering the cylinder from
+the water-jacket, but also to be sufficiently strong to withstand the
+pressure generated in the cylinder when the charge is fired. For this
+purpose specially prepared coppered asbestos rings are used, which will
+stand both water and intense heat. Sometimes a copper ring alone is
+employed to make the joint. At the front end the liner is just a good
+fit, and enters the bed easily, and a couple of bolts fitted in
+corresponding lugs on the liner, pass through the back end of cylinder
+casting, so that by tightening up these the joint at back end is made
+secure. A small groove is cut on a flange, and a rubber ring, of about
+1/4-in. sectional diameter, is inserted here when the liner is fitted
+into the cylinder casting. This makes the water-jacket joint at the
+front end.
+
+[Illustration: FIG. 3.]
+
+[Illustration: FIG. 5.]
+
+[Illustration: FIG. 4.]
+
+Lugs are provided on the bed and cylinder castings, and are bored to
+receive steel bolts--three are sufficient, provided the metal in and
+around these lugs is not pinched. In some cases a continuous flange is
+provided on both bed and cylinder, and a number of bolts inserted all
+the way round. This, however, is unnecessary, and has a somewhat clumsy
+appearance. When these bolts are tightened up, the cylinder and liner
+are clamped firmly to the bed; but the liner being free at the open end,
+can expand longitudinally without causing stresses in the cylinder
+casting.
+
+The combustion chamber K is virtually part of the cylinder, and has
+approximately equal to one-fourth the total volume of the cylinder. The
+shape varies somewhat in different makes of engines; in some it is
+rectangular, with all the corners well rounded off; in others it is
+practically a continuation of the cylinder, _i.e._, it is circular in
+cross-section, with the back end more or less spherical; while, again,
+it is made slightly oval in cross-section; but in every case the corners
+should be _well_ curved and rounded off, so that there is no one part
+which is liable to become heated disproportionately with the rest of the
+casting; in fact, in the whole cylinder casting there should be no
+sudden change, but a uniformity in the thickness of the metal employed.
+This point should be carefully remembered, although it applies more
+particularly to those parts of the casting subjected to higher
+temperatures than the rest.
+
+The main bearings are usually of brass or gun-metal, and are adjusted
+for running in the same manner as any steam or other engines would be.
+The "brasses" are in halves, and are held down by the cast-iron caps, as
+shown in fig. 1.
+
+These bearings require extremely little attention, and do not show the
+wear and tear of running nearly so soon as the connecting-rod brasses.
+These, too, are usually of brass or gun-metal; but there are various
+forms of construction employed in connection with the back end or piston
+pin bearings. On very small engines the connecting rod is swollen at the
+back end in the forging, and then machined up and drilled, as shown in
+fig. 3. In this hole the brasses are inserted after being scraped up to
+a good fit on the piston pin.
+
+A flat is cut on one of the brasses, and a set screw is fitted, as
+shown, to prevent any movement of the latter after the final adjustment
+has been made. A lock nut should be used in conjunction with this set
+screw. Another method, and one more generally used on larger engines, is
+shown in fig. 4. In this case the brasses are larger than in the former,
+where they are virtually a split bush; here they have holes drilled in
+them to take the bolts, the latter usually and preferably being turned
+up to the shape shown in fig. 5.
+
+
+
+
+CHAPTER III
+
+HOW A GAS ENGINE WORKS
+
+
+The gas engine of the present day, although from a structural point of
+view is very different to the early engine, or even that of fifteen
+years ago, is, in respect to the principle upon which it works, very
+similar. The greater number of smaller power engines in use in this
+country work on what is known as the Otto or four-cycle principle; and
+it is with this class of engine we propose to deal.
+
+Reference to the various diagrams in the text will help considerably,
+and make it an easy matter for any reader hitherto totally unacquainted
+with such engines to see why and how they work.
+
+Coal-gas consists primarily of five other gases, mixed together in
+certain proportions, these proportions varying slightly in different
+parts of the country:--Hydrogen (H), 50; marsh gas (CH4), 38;
+carbon-monoxide, 4; olefines (C6H4), 4; nitrogen (N), 4.
+
+Gas _alone_ is not explosive; and before any practical use can be made
+of it, a considerable quantity of air has to be added, diluting it down
+to approximately ten parts air to one of pure gas. This mixture is _now_
+highly explosive.
+
+The reader will do well to bear these facts constantly in mind,
+especially when he is repairing, adjusting, or experimenting with a gas
+engine. We wish to emphasise this at the outset, because a consideration
+of these facts will keep cropping up throughout all our dealings with
+the gas engine, and if once a fairly clear conception is obtained of how
+gas will behave under certain and various conditions, half, or even more
+than half, our "troubles" will disappear; the cry that the gas engine
+has "gone wrong" will be heard less often, and users would soon learn
+that the gas engine is in reality as worthy of their confidence as any
+other form of power generator in common use.
+
+But to revert to the explanation of the cycle of operations. The cycle
+is completed in four strokes of the piston, _i.e._, two revolutions of
+the crank shaft.
+
+At the commencement of the first out-stroke (the charging or suction
+stroke) gas and air are admitted to the cylinder through the respective
+valves (fig. 6), and continue to be drawn in by what may be termed the
+sucking action of the piston, until the completion of this stroke (the
+_precise_ position of the closing and opening of the valves will be
+referred to later on). The next stroke (fig. 7) is the compression
+stroke. All the valves are closed whilst the piston moves inwards,
+compressing the gases, until at the end of this stroke, and at the
+instant of maximum compression, the highly explosive charge is fired by
+means of the hot tube or an electric spark, as the case may be. The
+ensuing stroke--the second out-stroke of the cycle--is the result of the
+explosion, the expanding gases driving the piston rapidly before them;
+this, then, is the expansion, or working stroke (fig. 8.)
+
+[Illustration: FIG. 6.--Commencement of first out-stroke suction or
+charging stroke. Gas and air valve about to open.]
+
+[Illustration: FIG. 7.--Compression stroke, during which all valves
+remain closed.]
+
+During the last--the second inward--stroke (fig. 9) the exhaust valve is
+opened, and the returning piston sweeps all the burnt gases (the product
+of combustion) out into the exhaust pipe and so into the atmosphere.
+This completes the cycle, and the piston, crank, and valves are in the
+same relative positions as formerly, and the same series of operations
+is repeated again and again. Of course, it is not always the case that
+both air _and_ gas valve are opened on the charging stroke; that depends
+upon the method employed to govern the speed of the engine. Supposing
+it were governed on the hit and miss principle (to be explained
+hereafter), the gas valve would be allowed to remain closed during the
+charging stroke, and air alone would be drawn into the cylinder, then
+compressed, but not being explosive would simply expand again on the
+working stroke, giving back nearly all the energy which was absorbed in
+compressing it, and finally be exhausted in the same manner as the burnt
+gases are.
+
+[Illustration: FIG. 8.--Second out stroke, showing position of valves
+during working stroke.]
+
+[Illustration: FIG. 9.--Second inward stroke, showing position of valves
+during the exhaust stroke.]
+
+[Illustration: FIG. 10.--First out-stroke, showing position of valves
+during the charging stroke.]
+
+Fig. 10 shows diagrammatically the position of crank, piston, and
+valves _during_ the charging stroke.
+
+[Illustration: FIG. 11.--Cross Section of Cylinder.]
+
+In figs. 1 and 2 we gave drawings of two gas engines, which are typical
+examples of modern practice. Huge strides have been made in recent years
+in gas-engine work, as regards both workmanship and efficiency, so that
+to-day we have in the gas engine a machine whose mechanical efficiency
+compares favourably with that of any other power generator, and whose
+thermal efficiency is very much greater.
+
+[Illustration: FIG. 12.--Longitudinal Section of Cylinder.]
+
+Figs. 11 and 12 show respectively a sectional end and side elevation of
+the cylinder, from which it will not be difficult for the reader,
+however unacquainted he may be with gas-engine work, to see how the
+various requirements and peculiarities of the engine should be
+considered and provided for.
+
+A most important desideratum in any machine or engine is that it shall
+be as simple in construction as ever possible; complicated mechanism
+should only be introduced when such addition or complication compensates
+adequately for what must necessarily be a higher first cost, and
+incidentally the greater wear and tear and attention involved. Figs. 11
+and 12 show what has been done to simplify the construction of the gas
+engine in recent years. The main feature in this case is the very
+get-at-able position of the two main valves--the air valve F and the
+exhaust E. These valves, as may be seen from the drawing, are capable of
+withdrawal after the cover of the combustion chamber has been removed.
+The latter is an iron casting, shaped and faced up to make an absolutely
+tight joint; no asbestos or any packing is used to make this joint--and
+is held in place by four studs, as shown. Thus, all that is necessary is
+to remove the four nuts, lift the cover off, then pull out the pins
+which keep the spiral springs in position, and withdraw the valves. The
+latter are seated direct on to the metal of the cylinder casting, the
+gun-metal bushes A and B acting as guides. Further reference to A (the
+mixer), which serves a twofold purpose, will be made later on.
+
+The gas valve and cock are mounted in a separate casting, which is
+carried by a couple of studs, the joint between this and cylinder being
+made with a piece of rubber insertion. The gas enters at the gas-cock,
+passes through the valve and port G, and round the annular space in the
+bush or "mixer" A, previously mentioned, and thence through a number of
+small holes in same, immediately below the seat of the air valve F. At
+the same time, pure air is drawn in _via_ the air box (as explained
+hereafter), through port L (fig. 11), and thence up the centre of bush A
+and over the small holes through which the gas is flowing. The two then
+thoroughly mix and enter the combustion chamber together as the air
+valve F is opened. This device produces a perfectly homogeneous mixture,
+which conduces in no small measure to perfect combustion when the
+explosion takes place, and upon which, to a very great extent, depends
+the efficiency of the engine. Besides possible loss in this direction,
+however, there is another source of waste which cannot be eliminated,
+and that is the heat taken away by the cooling water which surrounds the
+cylinder. As this loss is inevitable, the best thing we can do is to
+make it as small as possible. Theoretically, it would be no small
+advantage if we could work at very much higher temperatures than we do
+at the present time, and it is only certain mechanical difficulties
+which bar the way and so effectually prevent the already high thermal
+efficiency of the engine being greatly increased.
+
+It is no easy matter to overcome these difficulties completely, but
+improvements in this direction are continually being made, so that
+troubles which attended the gas-engine user years ago no longer exist.
+
+All that we require of the cooling water is that it shall keep certain
+working parts of the engine at a reasonable temperature; for instance,
+the cylinder must not be so hot as to deprive the lubricating oil of its
+property to lubricate, neither must the exhaust valve become so hot as
+to cause it to seize in the bush and stick up; but, beyond such
+considerations as these, the higher the temperature is at the
+commencement of each explosion the more efficient will the engine be.
+The object, then, is to do as little cooling as possible, and to apply
+the cooling effect at the right parts; hence the passages and chambers
+through which the cooling water circulates should be so arranged that
+those which require to be kept at a low temperature are in close
+proximity to the cooling water. On some of the engines of days gone by,
+the exhaust valve was carried in a large iron casting, this in turn
+being bolted to the cylinder casting and communicating with the
+combustion chamber by means of a port. Such an arrangement was found to
+be not only clumsy but inefficient; the water passages were small and
+difficult to get at; they readily furred up; and moreover, the joint
+between this casting and the cylinder was necessarily a water _and_
+explosion joint, and the fewer we have of these the better.
+
+The method--if it may be called a method--of overcoming or preventing
+the exhaust valve becoming too hot is, in the case of figs. 11 and 12,
+simply one of judicious arrangement and design. The cooling water enters
+by the inlet K (fig. 11), and circulates round the exhaust valve port X
+and valve E immediately, before becoming heated, thus keeping the
+hottest of the working parts of the engine at a suitable temperature;
+and the valve seat, being in direct metallic communication with the cold
+water, does not become burnt or pitted. On the other side of the exhaust
+valve we have the air valve and its passages, through which cool air is
+continually being drawn; this also helps to keep the exhaust valve cool.
+
+From this, then, we may conclude that overheating of the cylinder will
+not occur under normal conditions, given an engine of good design; but,
+if this trouble does arise, we may safely look first of all for some
+defect in the cooling water circulation. Some waters contain a greater
+amount of impurities than others, and consequently the water space may
+furr up more rapidly in one district than in another. But this deposit,
+even under the worst conditions, accumulates very slowly, and the
+operation of cleaning out the water-jacket is a very infrequent
+necessity. The exhaust valve, however, may become overheated if it is
+allowed to get into bad condition, _i.e._, leaky. Its seat should be
+well looked after, or the hot gases will blow past when it is
+presumably shut; and if this defect, slight though it may be to begin
+with, is allowed to develop, both the seat, the valve head, and the
+spindle will become burnt away and pitted, perhaps badly, due to the
+excessive heat.
+
+
+
+
+CHAPTER IV
+
+IGNITION DEVICES
+
+
+The ignition devices commonly employed may be divided into three main
+classes--the metal tube, the porcelain tube, and the electric ignition.
+These again may be subdivided: The first being either iron or nickel
+(hecknum as they are sometimes called); the second are of two
+kinds--single-ended and double-ended; and the third takes many forms
+which many of my readers are possibly well acquainted with, such as the
+magneto, the induction coil and trembler, and the high-tension magneto
+ignition, the latter device having been used successfully on various
+occasions, though not yet universally adopted.
+
+The first-named have one or two advantages over the nickel tube. They
+are very inexpensive, and are easily heated to the required temperature;
+moreover, they can be made at home, should occasion demand. On the other
+hand, they are not so durable, have a very uncertain life, and
+consequently need renewing frequently--their average life being not
+more than 60 working hours. Fig. 13 gives an outline drawing of an iron
+tube, with its burner and chimney fixed in position. The tube is very
+similar to a piece of 1/4-in. gas-barrel, closed up at one end and a
+taper thread (1/4-in. gas) cut on the other; in fact, gas-barrel may be
+used for making these tubes at home--and measure about 7 or 8 in. over
+all It is screwed into a firing block, which in turn is screwed into the
+combustion chamber end, so that when right home it is in such position
+that the tube stands quite vertical. The section of the tube, fig. 13,
+shows the condition it gets into after having been in use some time. The
+bore, it will be seen, has become almost completely closed up, so that
+there is practically no communication between the hot part of the tube
+and the combustion chamber. This closing up of the bore is very gradual,
+and it is in the early stages of this process that erratic firing is
+likely to occur; sometimes the charge will be successfully fired and
+sometimes not. It may be as well to mention here that the length of the
+tube, although to a certain extent immaterial, should neither be
+excessively long nor abnormally short, the precise length varying with
+the size of the engine. A 1/4-in. tube, 8 ins. long, may be used
+successfully on engines ranging from 1/2 to 6 horse-power, provided a
+suitable burner is fitted enabling the tube to be heated at any required
+spot. After the first charge has been fired, and the exhaust takes
+place, practically all the burnt gases are cleared out of the cylinder,
+but a small amount of these will generally remain in the tube and the
+bore of the firing block. On the ensuing compression stroke these inert
+gases are compressed to the far end of the tube, thus making way for the
+explosive mixture to reach the hot portion, and explode, thus sending a
+jet of flame into the main volume of the mixture which is immediately
+ignited. Hence there is no advantage in having a tube too long, while,
+on the other hand, it _must_ not be too short.
+
+[Illustration: FIG. 13.]
+
+[Illustration: FIG. 14.]
+
+[Illustration: FIG. 15.]
+
+The asbestos lining, shown in fig. 13, may be of various thicknesses,
+according to the size of the chimney and the tube; the reason for this
+will be apparent to many; but being a most important factor in the
+heating of the tube, and consequently the working of the engine, it will
+be advisable to deal with this point more fully.
+
+Due mainly to the peculiar behaviour of iron tubes under heat and
+internal pressure, it is always advisable to look to them first of all
+when the engine shows signs of missing fire; and to always examine the
+bore of a fresh one, and ascertain that it is perfectly clear before
+putting it in. The adjustment of the ignition tube, although one of the
+most important and necessary to be made on the whole engine, is in
+itself a perfectly simple matter. It must be understood that the
+ignition tube cannot, with the ordinary means at our disposal, be kept
+at too high a temperature; but it must not be assumed that either the
+_size_ of the flame, or the _time_ the flame has been alight, is
+conclusive evidence that the tube is, or ought to be, sufficiently hot
+to fire the charge successfully. It is an uncommon thing to hear a man
+exclaim--after it has been pointed out that his tube is practically
+cold--"Why, it's been alight for hours!"
+
+If such is the case with you, reader, you may very rightly assume that
+the burner is not properly adjusted, and so does not give the _right
+kind of flame_.
+
+In order to get the hottest possible flame, the quantity of gas and air
+must be mixed in the right proportions. A common fault is that there is
+too much gas allowed to flow through the nipple, compared with the
+amount of air being drawn in at the air aperture, fig. 13. The result
+is, we get a flame of great length, but one which is not at all suited
+to our requirements; and instead of giving up its heat to the tube and
+the asbestos lining of the chimney, a large amount of gas we are
+presumably burning _in_ the chimney is not being burnt there at all,
+for, on applying a light just above the chimney top, a quantity of this
+gas we are wasting will be seen to burn with a flickering blue flame.
+
+To put matters right, it is necessary to do one of two things--either
+cut down the supply of gas or increase the air-supply. Providing the air
+aperture is normal, _i.e._, the same size as it was originally, it is
+better to adjust the _gas_, which may be done by tapping up the nipple
+N, as indicated in the enlarged sketch, fig. 14, until just the right
+amount of gas can flow.
+
+As a rule, if there is too much air, the flame will burn with a loud
+roaring noise, and is liable to fire back. The nipple should then be
+opened out with a small reamer--the tang of a small file, ground to a
+long taper point, makes an admirable tool for this purpose. Whether the
+burner is of the ordinary bunsen type, or the ring or stove type, the
+above remarks apply, as in every case the flow of gas is governed by the
+size of the orifice through which it flows.
+
+There is no need to use anything beyond a touch of oil when putting in a
+new tube, in order to make a perfectly tight joint; white or red lead
+are quite unnecessary, and are liable to make it a troublesome matter to
+remove the tube on future occasions. Neither should undue force be
+applied when putting in new tubes; it is liable to wear the thread in
+the firing block, which results in a partial stoppage of the ignition
+hole, as indicated in fig. 15. This is especially the case if we happen
+to get hold of a tube with its screwed part slightly smaller than usual.
+
+The asbestos with which the chimney is lined should be about 1/8 in.
+thick, and, when renewing, the same thickness should be used as
+originally. A thicker board will reduce the annular space round the
+tube, and will have a choking effect on the flame--much the same as
+referred to above, when there is too much gas and not enough air. A
+simple method of lining the chimney is to cut a block of wood to the
+inside dimensions of the chimney, less 1/4 in. in width and thickness,
+then soften the asbestos cardboard by immersing in water, and bend it
+round the wood, cutting off to the required size, _i.e._, till the two
+edges form a neat butt joint. It can be allowed to remain on the mould
+until dry--when it will retain its shape--or can be put into the chimney
+straight away, if it is wanted for use immediately. In the latter case,
+however, it will be some fifteen minutes or so before the tube will
+attain its working temperature. Asbestos linings gradually become worn
+and ragged, and small flakes are apt to detach themselves and fall down
+into the burner, which, of course, prevents the flame playing as it
+should around the tube. In such cases it is not always necessary to fit
+a new lining; if the chimney is removed, the loose flakes shaken out and
+the asbestos well damped and patted down with a wooden or steel
+foot-rule or other suitably shaped tool, it will be fit for another long
+spell of work.
+
+The nickel or hecknum tubes are treated in the same manner as the iron,
+but, as we mentioned before, are more durable, but require more heating
+to get them up to a workable temperature. Their greater first cost is
+compensated to some extent by makers in some cases guaranteeing them for
+six months.
+
+Of the porcelain ignition devices, we will deal with the double-ended
+tube first, it being the more commonly used of the two in this country.
+This form of tube is usually about 3 in. long, 1/2 in. diameter, and
+open at both ends. It may be mounted in a metal casting, in form not
+unlike the small gas stoves for heating soldering irons. It is heated
+the greater part of its length by a couple of rows of gas jets, and is
+frequently surrounded by an asbestos lining. The whole arrangement is
+in reality a tiny furnace. When in position for working, one end of the
+tube is open to the ignition passage leading and communicating with the
+combustion chamber, while the other end is sealed, through butting up
+against a metal cap or plate. An asbestos washer is interposed between
+the tube at each end and the metal it bears against, thus making a more
+or less flexible joint. A thumb screw is arranged at the outside end of
+the tube, by means of which pressure can be applied to clamp it up
+between the washers to the desired extent. Some care has to be exercised
+in adjusting this form of tube for running. When heated to the working
+temperature it, of course, expands, so that, if tightened up too much
+when cold, it is under a fairly high compression; and when the engine is
+started, and the explosion takes place, it not infrequently bursts, if
+there is not sufficient "give" in the washers to allow for the
+expansion. On the other hand, if not clamped up sufficiently tight to
+start with, when the explosion occurs, the washer at one or each end is
+blown out. This adjustment has to be made to a nicety, and, although a
+somewhat difficult matter, success may be attained after one or two
+trials. It is advisable, after a new tube has been put in, to start up
+the engine gently, _i.e._, with less than the normal supply of gas, and
+increase to the full amount gradually whilst running. This may be done
+by simply opening the gas-cock on engine partially in the first place.
+
+The single-ended porcelain tube is not so well known here as on the
+continent; why, we cannot say; certainly it is preferable in every way.
+We give a few illustrations, showing the method of using this tube.
+
+Figs. 16 and 17 show the general arrangement of tube and chimney and the
+manner in which they are fixed to the cylinder. The device consists
+primarily of three parts--the body or chimney B, the cover C, and the
+tube itself T. The body is a light iron casting, carried by a couple of
+studs SS, which are either screwed into the firing block F, or direct
+into the metal of the cylinder casting if no firing-block is used; the
+latter may very well be dispensed with in the smaller-sized engines.
+
+The tube is made of thin porcelain, slightly bell-mouthed at its open
+end, and is mounted in a thick metal washer W, as shown in fig. 18 in
+section, the joint being made with a little asbestos paper, moistened.
+
+The block F and the face of the body B (fig. 16) are recessed to take
+the washer W easily, but the depth of both recesses taken together must
+be about 1/16 in. less than the thickness of the washer W; thus, when
+the tube is placed in position between the body B and the block F, and
+the former screwed up by means of the two nuts, as shown in the figure
+16, the effect is to clamp the _washer_ which carries the tube, but _not
+the porcelain tube itself_.
+
+[Illustration: FIG. 16.]
+
+[Illustration: FIG. 17.]
+
+[Illustration: FIG. 18.]
+
+The latter is left perfectly free to expand; and yet, owing to its
+particular shape, the pressure in the cylinder during the compression
+and explosion stroke only tends to make the joint between the tube and
+washer more secure. The action of this ignition device depends upon the
+tube heater H, which is merely a small bunsen burner, the flame of which
+impinges on the tube at one particular spot, raising it to a very high
+temperature--almost white heat. Most of my readers will know the
+formation of the bunsen flame. It in composed of two distinct zones. The
+inner one, marked A in fig. 18, is a perfectly cold part of the flame,
+and appears to be a pale-blue coloured cone.
+
+It is the outer zone which is the hot portion of the flame, hence this
+part _only_ must be allowed to play on the tube. The tip of the blue
+cone A must be kept about 1/4 in. below the tube, in order to ensure the
+hottest part of the flame impinging precisely where the heat is
+required.
+
+The total length of the whole flame is, to a certain extent, immaterial;
+but, generally speaking, it should be adjusted so that the length of the
+inner cone A is about 1 in. or 1-1/4 in. The same methods which we
+described in the early part of this chapter can be employed in the
+adjustment of this burner, but some care should be exercised to get the
+correct flame length.
+
+The result of allowing the cold part of the flame to impinge on the tube
+is observable in fig. 18. The black spot indicated on the drawing
+actually appears as a black or sooty spot when looking at the tube under
+these conditions; but in reality no discoloration whatever takes place,
+the spot disappearing immediately the cone A is made shorter, or the
+burner H lowered in the chimney B, so that the tip of A is just below,
+and does not touch the tube at all.
+
+The adjustment of the length of cone A may be accomplished in two
+ways--(1) by keeping the supply of gas constant, and varying the amount
+of air admitted at aperture K, fig. 18; (2) by keeping the supply of air
+constant, and varying the amount of gas admitted through nipple N. The
+first method is to be preferred when it is necessary to make any slight
+adjustment due to the variation of gas pressure during the day, and may
+be accomplished by fitting a small sliding shield G, as shown in the
+figs. 16 and 17, and moving it round so that it covers, more or less,
+the aperture K. Thus the length of cone A may be adjusted to a nicety in
+a very few seconds. This shield keeps all draughts and puffs of wind
+from the fly-wheel away from the aperture, and helps the flame to burn
+very steadily. In the first place, of course, the flame will be
+regulated by opening out or tapping up the nipple N (an enlarged sketch
+of which is given in fig. 14), so that cone A is just about 1-1/4 in.
+long when air aperture is full open; but once this is done, any future
+adjustment can be made by throttling the air-supply, or raising or
+lowering the burner bodily, the set screw keeping it in any desired
+position (see fig. 17).
+
+From the foregoing remarks it will be seen that the most noteworthy
+features of this form of ignition are the ease and certainty with which
+the tube can be fixed in a few moments; that when the two nuts on the
+studs SS have been tightened up there is no likelihood of the joints
+being "blown," for, as we said before, only the metal washer is clamped
+up, the porcelain tube itself being as free to expand as it was before.
+It is also at once obvious when any adjustment of the flame is
+necessary; there need be no uncertainty as to whether the tube is hot
+enough or not.
+
+
+
+
+CHAPTER V
+
+MAGNETO IGNITION
+
+
+The third form of ignition we have to deal with is the electric.
+
+There are a great number of different types made and used, but for
+gas-engine use perhaps that known as the magneto ignition is the most
+satisfactory. With this form, neither accumulators, dry batteries, or
+spark coils are required, and consequently a greater simplicity is
+arrived at than would otherwise be the case.
+
+In fig. 19 we show diagrammatically the ordinary form of magneto
+machine. Virtually it is a small dynamo which is fixed to the side of
+cylinder casting, and is operated in the manner shortly to be described.
+As we do not propose to enter into more than a brief explanation of why
+and how this apparatus generates current to produce the required spark,
+perhaps a simple analogy will make matters most intelligible to any
+reader not well acquainted with electrical phenomena. We know that when
+a current of electricity is flowing in a wire, and the wire be suddenly
+broken, a spark will occur at the point of breakage. This fact may be
+observed in an ordinary electric bell when ringing; at the tip of the
+contact breaker a number of tiny sparks may be seen to occur, due to the
+rapid make and break of the current flowing in the circuit. Precisely
+the same action takes place in our magneto-igniter, but, instead of a
+multitude of tiny sparks, we produce one at a time, at definite
+intervals, viz., at the commencement of each explosion stroke.
+
+[Illustration: FIG. 19.]
+
+In the later form of magneto machines there is a soft iron sleeve
+between the magnet poles and the armature. The former is connected to a
+system of levers by which a reciprocating motion is imparted to it by
+means of a suitably arranged cam on the side shaft. It has been found
+that better results are obtained by causing the magnetic field to move
+relative to the armature winding than to move the latter through a
+stationary field. Reference to the diagrams, figs. 20 and 21, will make
+this clear.
+
+In fig. 19 the cam C is shown just on the point of allowing the lever L
+to fly back into its normal position, due to the action of the springs
+comprising a dashpot S. As the cam rotates, it pushes the lever L to the
+left, the sleeve (or virtually the armature A) is also rotated through a
+portion of a revolution comparatively slowly; but as soon as L is
+released, the sleeve (or armature) flies back again almost
+instantaneously and for the moment is generating a current in the same
+manner as would any ordinary continuous current dynamo.
+
+[Illustration: FIG. 20.]
+
+[Illustration: FIG. 21.]
+
+At the instant the maximum current is being generated, the circuit is
+broken by means of the contact breaker D, fig. 19, which we show in
+detail in fig. 22. The latter is mounted on the end of the combustion
+chamber, and consists of two parts, D and P.
+
+[Illustration: FIG. 22.]
+
+D is an easy fit in the hole bored to receive it, and has a mushroom
+valve head and seating, as shown, so that it moves readily when struck
+by the projection E on the rod R (fig. 19); but yet, acting in the
+manner of a non-return valve, it allows no gas to escape when the
+explosion takes place in the cylinder. D is therefore in direct metallic
+communication with the engine frame and earth.
+
+P is a fixed metal pin, carefully insulated from all contact with the
+engine frame and earth. To this pin one end of the armature winding is
+connected, whilst the other end is connected to the engine frame.
+
+Thus a closed circuit is formed, and when the current is generated it
+flows from one terminal of magneto through wire to pin P, on to D,
+through D to earth (_i.e._, engine frame), and so back to other terminal
+on magneto.
+
+And as the circuit is broken between D and P, we obtain a spark, as
+previously explained, which may be timed to take place by adjusting the
+position of cam C on side shaft relatively to the position of piston.
+
+It may be said that the position of the magneto-igniter is immaterial;
+it will be fixed in different positions on different types of engines,
+and so long as the operating mechanism is simple and effective, _i.e._,
+as direct as is practicable, it works well, and requires little
+attention. The timing of the spark will be dealt with in the chapter on
+Cams and Valve Settings.
+
+
+
+
+CHAPTER VI
+
+GOVERNING
+
+
+The devices for governing the speed of the engine may be divided,
+broadly speaking, into two classes--the inertia or hit and miss
+governor, and the centrifugal. Of the latter type we will give an
+instance first. In figs. 23 and 24 the governor gear is shown
+diagrammatically, consisting of a couple of weights WW suspended from a
+vertical spindle. These fly apart when caused to revolve by the bevel
+wheel gearing BB, and raise the sleeve S to a greater or lesser extent.
+A recess in the latter engages a lever arm L, through which the vertical
+movement of the sleeve S is converted into a horizontal movement of the
+sleeve T. The latter is carried by the valve lever P, and is virtually a
+roller which engages with one or other of the steps of the cam C,
+according to the speed of the engine. The object of this arrangement is
+to keep the ratio of air to gas uniform throughout all variations of
+load. The gas and air valve are shown as both being operated by the same
+lever P, the accurate timing of the latter being obtained by means of
+set screws.
+
+[Illustration: FIG. 23.]
+
+[Illustration: FIG. 24.]
+
+Messrs Dougill & Co.'s engines are fitted with a step down cam and
+governor such as this. The centrifugal governor is often arranged so
+that instead of the charge being merely reduced in volume, the whole
+charge is cut out, and no explosion whatever takes place. (In this
+respect the same results are obtained as when a hit and miss governor is
+used, and the latter form therefore is to be preferred, especially on
+small engines, where the difference between the indicated power and the
+brake power is always, even under the best conditions, fairly great.)
+
+In this case the governor lever only operates the gas valve; the air
+valve being opened on every charging or suction stroke, whether gas is
+admitted or not.
+
+Another application of the centrifugal governor is to suspend a distance
+piece on the end of the governor lever, so that at normal speed this
+distance piece is interposed between the gas valve spindle and the lever
+operating it. In that case the gas valve will be opened. But if the
+speed is above the normal, the distance piece will be raised clear of
+the valve spindle, and the opening mechanism (driven by a cam on the
+side shaft) will simply move forward and recede again without ever
+touching the gas valve.
+
+There are any number of movements which have been, and there are many
+more which could be, devised to give the same result; and it depends
+principally upon the form of engine in question which device we adopt.
+
+The simplest and most direct action is, however, always the best;
+complicated mechanism is to be deprecated, especially on small engines.
+For this reason is the inertia governor more generally fitted to such
+engines.
+
+[Illustration: FIG. 25.]
+
+A simple form of this governor is shown in fig. 25. The gas valve V is
+shown on its seating. It is screwed into a pecker block B, and pinned as
+shown. The latter should be of cast steel, tempered to a straw colour;
+or if mild steel or iron is used, it must be well case-hardened, in
+order to resist wear. The pecker P (also tempered hard) is mounted on
+the cast-iron weight W, which in turn is pivoted on the valve lever L.
+It will be seen that the weight W (which is only held in the position
+shown by the spring S) will tend to lag behind when a sudden upward
+motion is imparted to the lever L. Thus it depends upon the degree of
+suddenness with which L moves whether the pecker P remains in the same
+relative position to the lever as the latter travels upwards and engages
+with the pecker block B, or whether it misses it and simply slides over
+the face of the block. The adjustment of the spring S is effected by
+screwing up or slacking out the milled nuts T; and on the degree to
+which this spring is compressed depends the sensitiveness of the
+governor, and consequently the speed of the engine. To obtain accurate
+and steady governing with this type of mechanism it is essential that
+the weight be perfectly free on its spindle, and that nothing but the
+spring S holds, or tends to hold, it in the position shown. On this
+account it is advisable to provide a "lip" on the pecker block, as
+shown, to keep the area of contact as small as possible. This
+effectually prevents any sticking, should a superfluity of oil happen to
+get on either block or pecker. For similar reasons there should be some
+clearance between A and the pecker, _i.e._, the latter should only bear
+at one point and not bed flat against A.
+
+Another form of inertia governor is shown in fig. 26 of the hit and miss
+type, which is employed by Messrs Capel & Co. on many of their engines.
+
+It consists of three main parts--the brass arm L carried on a stud D, on
+which it is free to move; the weight W, which carries the pecker P
+pivoted at the upper end of L; and the pecker block B, which engages the
+pecker when the engine requires a charge of gas.
+
+The governing action is dependent upon the shape of the operating cam
+from X to Y. (In the case already dealt with, the lever L serves to
+operate both air and gas valves, and so one cam only is necessary; but
+in this instance the gas valve is operated by a separate cam, and a
+greater nicety of adjustment is obtainable.)
+
+[Illustration: FIG. 26.]
+
+If the speed of the engine is sufficiently high, the arm L is thrust
+forward at such a rate that the weight W tends to lag behind, with the
+result that P is raised above the notch in B, as shown by the dotted
+lines in drawing. On the other hand, when the speed is too low, the arm
+L will not be thrust forward with so great a degree of suddenness, the
+weight W will have time to move with L, and the relative position of W
+and P to L will remain the same. Hence, in the first case, when a
+_further_ forward movement is given to L by the cam, the pecker P is
+clear of B, and omits to open the gas valve V; in the second case, P
+engages with B, and the gas valve is held open during the time the
+portion of cam Y to Z is passing over the roller R on arm L.
+
+The great drawback to some forms of governors is not that they fail to
+govern well when new, but that no provision is made to ensure them
+working steadily when a bit worn. The shape of the cam has everything to
+do with the regular working of this form of governor.
+
+Supposing our cam was of the shape shown in fig. 27, _i.e._, the
+governing and opening portion all in one curve, it would cause the
+pecker to move both _forward_ and in an _upward_ direction at the _same
+time_, so that at the moment of engaging B, P might still be moving in
+an upward direction, which would cause uncertainty of action, especially
+if the tips of the engaging members were at all blunt through wear; and,
+in all probability, P would fly off B after partially opening the gas
+valve.
+
+This behaviour is very undesirable, as the small quantity of gas so
+admitted to the cylinder is quite useless, and a sheer waste is
+incurred. With the governing arrangement shown in fig. 26, this trouble
+does not exist. The cam is so designed that the first rise from X to A
+determines whether or not the valve is to be opened; the curve from A to
+Y is struck from the centre of the side shaft; thus, during that
+portion of the revolution the arm L is stationary, and the pecker at the
+same instant takes up a definite position either in the notch in B or on
+top of it, and is ready to open the valve if the speed of the engine is
+such as to require an explosion, or simply to slide over the top of B,
+allowing the valve to remain closed. It is most interesting to observe
+the action of this governor; when an engine fitted with one is running
+very slowly, the three distinct movements of the pecker P may be clearly
+discerned as the respective portions of the cam pass over the small
+roller R.
+
+[Illustration: FIG. 27.]
+
+
+
+
+CHAPTER VII
+
+CAMS AND VALVE SETTINGS
+
+
+With the gas, as with any other kind of engine, the valve settings are
+of primary importance. On very small engines it is often the case that
+only the exhaust valve is operated mechanically.
+
+Again, there are several well-known makes which operate the gas and
+exhaust mechanically while the air valve is opened by suction alone.
+Though opinions differ as to which is the best course to take, there can
+be little doubt that, with all three valves mechanically operated, a
+greater nicety of adjustment is obtainable than would be otherwise
+possible. And provided the working parts are neatly made and finished,
+they will take but little power to drive them; and such loss would be
+compensated by the additional power and efficiency obtained from the
+engine, due to satisfactory and correct adjustment.
+
+In fig. 28 we give a diagram showing the exact positions of the crank
+when the gas, air, and exhaust valves open and close respectively, under
+normal conditions of working. The solid circle represents the first
+revolution of the crank shaft, starting from the commencement of the
+suction stroke, and the dotted circle the second revolution, during
+which the explosion and exhaust strokes take place; the dotted
+horizontal line shows the position of crank at the back and front dead
+centres.
+
+As a clear conception of why certain things happen under certain
+conditions is most desirable, we will first describe the operation of
+marking off the cams which operate the respective valve levers, and then
+discuss the effect of various "settings" of the valves on the running of
+the engine.
+
+[Illustration: FIG. 28.]
+
+Assuming that we are still dealing with the Otto cycle engine, the cam
+or side shaft will revolve at precisely half the speed of the crank
+shaft. This 2 to 1 motion is obtained by means of toothed wheels, or a
+screw gear. In the former case, where plain or bevel cog-wheels are
+employed, the one fixed on the crank shaft must be exactly half the
+diameter of the one on the side shaft, _i.e._, it must have one half the
+number of teeth. On the other hand, if a screw gear is used, the
+relative diameters of the two wheels may vary, but the pitch of the
+teeth on the one must be twice that of the other. These wheels sometimes
+have the teeth or thread formed in the casting, and sometimes they are
+cut after a plain casting has been made. The latter kind are, needless
+to say, better than the former, which often require filing up in order
+to make every tooth alike, and ensure sweet running.
+
+We know already in what positions our crank has to be at the opening and
+closing of the three valves, and with the aid of the diagram, fig. 28,
+we can determine the size of the cams. In fig. 29, S is the side shaft
+to which the cams have to be keyed, R the roller on valve lever, the
+latter being represented by the centre lines LL, as all we require to
+find is the motion this lever will transmit to the valve, the spindle of
+which is shown at V.
+
+Fig. 30 shows diagrammatically the position of crank at the opening and
+closing of the air valve. From this we see that the angle through which
+the crank travels during the time the air valve is open is equal to the
+obtuse angle ABC. Now, as the side shaft S revolves at half the speed of
+crank, it is obvious that the former will travel through only half that
+angle in the same space of time, _i.e._, through an angle equal to ABD.
+We can now transfer this angle on to S, fig. 29, and draw two lines SE,
+SF, cutting a circle GHJ, representing the back of the cam, which latter
+passes in front of the roller R without causing any movement of the
+lever L.
+
+[Illustration: FIG. 29.]
+
+[Illustration: FIG. 30.]
+
+[Illustration: FIG. 31.]
+
+It will be seen that by drawing a line forming a tangent to the circle
+GHJ at F and another at E, and producing these, they will meet at point
+K. Consequently, as the side shaft rotates in the direction indicated,
+the lever L will _begin_ to open the valve V when the cam is in the
+position shown in fig. 29, reach a maximum opening at K, and finally
+close when the cam has moved so that point E is now where F was. With a
+cam of this shape, however, a considerable portion of the stroke would
+have passed before the valve was raised any _appreciable_ distance off
+its seat; it would only be fully open for an instant, viz., when K was
+passing over R, and would begin to close again directly.
+
+Moreover, if the engine were running at even a slow speed, the motion
+imparted to lever L would be indefinite; and this, especially if the
+governor is fitted to the air valve lever, as in fig. 25, is very
+undesirable. Therefore, to obtain a definite opening we must set out the
+cam, as shown in fig. 31. In this diagram the roller is shown standing
+clear of the back of cam by about 1/16 in. A line MN is then drawn,
+forming a tangent to both roller R and circle GHJ at points F and O
+respectively. This gives us the opening portion of cam. Then from the
+centre S with radius SF describe the arc FE (shown dotted in fig. 31),
+and set off the angle required (ABD, fig. 30), as previously explained.
+Through point E draw a line forming a tangent to circle GHJ, and produce
+it towards P. This line gives us the closing portion of cam. The
+distance W is of course variable, according to the amount of lift we
+give the valve. By comparing these two diagrams it will be seen that in
+both cases the valve will be opened the same length of time, but in
+first case the motion will be indefinite and uncertain. In practice the
+corners are rounded off somewhat, in order to obtain a steady motion;
+and when the air cam is also the governing cam, it is advisable to round
+off the opening face, as indicated in fig. 32. Upon the shape of this
+face both the sensitiveness and the life of the governor gear depends.
+If it is nicely rounded off, giving a gradual rise, very little tension
+(or compression, as the case may be) of the controlling spring will be
+necessary to give the required speed to engine; whereas, if the rise is
+sudden, the spring will have to be screwed up tighter, and, if uneven
+and lumpy (_i.e._, not a fair curve), the result will, of course, be
+erratic governing.
+
+[Illustration: FIG. 32.]
+
+A certain amount of clearance should always be provided between the
+roller and the back of cam (compare figs. 29 and 31), that is, the
+roller should not bear against the cam, except during that portion of
+the stroke in which it is actually operating the valve, viz., from F to
+E (fig. 31). A small stop interposed between the lever and some
+convenient part of the engine, such as the side-shaft bracket bearing,
+answers this purpose.
+
+[Illustration: FIG. 33.]
+
+[Illustration: FIG. 34.]
+
+The size and shape of the exhaust cam is found in the same manner as
+above described; the angle through which it operates is greater than
+that of the air cam, and is shown in fig. 33. A fair margin should be
+allowed for filing or machining these castings up; the shape and sizes
+arrived at by the above described method being finished measurements.
+Fig. 34 gives the outline of an exhaust cam worked out from the setting
+diagram, fig. 33.
+
+[Illustration: FIG. 35.]
+
+[Illustration: FIG. 37.]
+
+[Illustration: FIG. 41.]
+
+[Illustration: FIG. 42.]
+
+We may now consider the relative positions these two cams will occupy
+when keyed up on the side shaft. Assuming that we have both cams
+finished to the proper shape and size, and the keyway cut in the side
+shaft, we can commence to mark off the position of keyway in the air
+cam. With the crank in the position shown in fig. 35, the air cam is
+slipped on to the side shaft and brought to the position shown in fig.
+32. The keyway being already cut in the side shaft, the position for
+that in the cam may be scribed off, as shown by dotted lines (fig. 32),
+the cam removed, and the keyway cut. It is as well, however, to check
+this mark by turning the crank round to position shown in fig. 37,
+_i.e._, the closing of air valve. The side shaft will also turn through
+exactly half this angle, so that when the cam is again slipped on the
+latter, the scriber marks and keyway in shaft should be exactly in line,
+as they were in fig. 32, and the fall of the cam--the closing
+portion--should just be touching roller R, but not sufficient to keep
+the valve open (see fig. 38). The slightest movement of the crank from
+this point in a forward direction should result in a little play being
+felt in the lever L, assuming that the cam is also moved just enough to
+keep the scriber marks in line with the existing keyway.
+
+[Illustration: FIG. 36.]
+
+[Illustration: FIG. 38.]
+
+[Illustration: FIG. 39.]
+
+By these operations it will be at once evident whether the cam is too
+large or too small. Supposing it is too small, we will obtain two sets
+of marks indicating the position of keyway, as shown in fig. 39, and it
+is obvious that we must give the lever less play by screwing up the set
+screws shown in fig. 11. The effect of this is to cause the valve to
+open earlier and close later than it would if the play were greater; as
+it would were the operating portion of cam larger. A minimum amount of
+play must always be allowed, however. When two sets of marks are
+obtained, the mean must be taken and the keyway cut as shown by the
+thick lines in fig. 39. The exhaust cam in larger engines is usually
+made with a swelling on the opening portion, as shown in fig. 40, so
+that the valve is _very slightly_ opened some time before the crank has
+reached the position shown in fig. 41. Fig. 42 shows position of crank
+at the close of exhaust valve, and the two last-mentioned diagrams
+correspond with the two positions in which the exhaust cam is shown in
+fig. 34. The small lump on the back of exhaust cam, fig. 40, is only
+required on engines above 3 B.H.P. to relieve the compression on the
+compression stroke when starting up. By moving the roller R on valve
+lever longitudinally, so that it engages both parts of cam as they pass
+in front of it, the exhaust valve is held open during a small portion of
+the compression stroke, usually closing when the crank has reached the
+bottom centre.
+
+Referring again to fig. 26, this gas or governor cam may be set out, and
+the keyway marked on the same principle as already described for the air
+and exhaust valves. An end view of the three cams keyed up on the side
+shaft is given in fig. 40A. In small engines it is convenient to have
+the air and exhaust cams made in one casting, when one key only will be
+required. On some engines, instead of employing a movable roller or
+valve lever, the exhaust cam is fitted on side shaft with a
+"feather"--_i.e._, a headless key--and the cam being capable of
+longitudinal movement, such movement being controlled by a small lever
+or handle, called the half-compression lever.
+
+[Illustration: FIG. 40.]
+
+[Illustration: FIG. 40A.]
+
+Having once thoroughly grasped the important part the cams play in the
+working of the engine, it will be an easy matter to adjust the valve
+settings, and to keep them adjusted correctly. The effect of a wrong
+setting will then be strikingly apparent. On small engines a separate
+cam to operate the gas valve is not a necessity; and the practice of
+fitting the gas valve spindle (or the pecker, the effect would be the
+same) with a device for increasing or diminishing its length, is also
+unnecessary and unsound.
+
+The wear on a well-designed gas valve operating mechanism is practically
+nil; and even if there was wear, the effect would be to cause the valve
+to open a trifle later and close sooner than it would otherwise, _i.e._,
+it would remain open a shorter time during each charging stroke. This in
+turn (other conditions remaining the same) would give us a weaker
+mixture; and although too weak a mixture is preferable to a too rich
+one, we should have to adopt some means of increasing the richness of
+the mixture; otherwise the maximum power of the engine would soon be
+seen to diminish.
+
+To get the mixture normal again we must either enlarge the gas inlet or
+cut down the air-supply somewhat, and so keep the proportions the same.
+That is to say, the quality of the mixture is dependent upon the
+relative dimension of the gas and air inlets. We know by actual trial
+that if at the completion of the charging stroke the pressure in the
+cylinder is approximately that of the atmosphere, better results are
+obtained than when the pressure is considerably below that of the
+atmosphere. Thus, the larger we make the inlet ports (but still
+retaining correct relative dimensions) the more readily will the mixture
+be drawn into the cylinder as the piston moves forward, tending to
+create a vacuum. Of the two courses open to us to retain a good mixture
+it is preferable to open out the gas-supply, for by cutting down the
+air-supply, and sucking the gas in, due to the partial vacuum being
+formed, we should be keeping the proportions correct at the expense of
+reducing the total volume of the explosive mixture (more strictly
+speaking, the density of the charge) admitted to the cylinder.
+
+Under normal conditions it is not necessary to create a high vacuum to
+suck the gas into the cylinder, but it is as well to understand what
+results we would tend to produce, did we work on these lines. Of course,
+with small high-speed engines fitted with suction air valve, the vacuum
+is higher than it would be in slow-speed engines with mechanically
+operated valves. If we take an extreme case as an example, where, to get
+any gas to speak of into the cylinder the air-supply would have to be
+cut down or throttled to an abnormal extent, we will realise at once
+that such a small quantity of both air and gas would have been drawn in,
+and consequently the mixture would be so rarefied that on the
+compression stroke the pressure would possibly be extremely low and
+totally inadequate to produce efficient working. Moreover, working at
+such a high vacuum as this would not only prevent us obtaining a normal
+explosion in the cylinder, but would upset the working of the exhaust
+valve. The latter being held down on its seat during the suction stroke
+by means of a spiral spring would be lifted off its seat by suction (the
+partial vacuum in the cylinder), and any burnt gases which happened to
+be hanging about in the exhaust port or pipe would be drawn into the
+cylinder again, and tend to damp the ensuing explosion. Too early
+closing of the exhaust should be avoided almost as rigorously as too
+late. The latter will affect the working in a similar way to the exhaust
+being lifted on the charging stroke by suction; on the other hand, if it
+closes too soon, the entire volume of burnt gases will not have been
+swept out of the cylinder, and the effect will again be to damp the
+following explosion.
+
+The gas valve opens just after the crank is above the back centre and
+closes just before the front centre is reached, that is, opening a
+little after the air valve and closing a shade before it, thus every
+particle of gas is used in the cylinder, due to a draught of air being
+drawn in after the gas valve has been closed.
+
+The settings of the valve being of primary importance, no matter what
+size engine we are dealing with, and being also the most confusing
+matter for anyone unacquainted with gas engines to grasp, it will not be
+out of place to suggest a simple method of checking these settings.
+
+Let us begin by pulling the fly-wheel round backwards until we feel the
+piston is on the compression stroke, then from this point--the crank
+being about 45 deg. above the front centre--pull the wheel round until the
+crank is in the position for the exhaust opening (see fig. 28). In this
+position there should be but the _slightest_ play in the exhaust lever,
+showing that the valve is _just_ on point of opening; and by keeping
+one's hand on the lever whilst the fly-wheel is pulled round _very
+slowly_ (it is a good plan to get some one else to do the pulling
+round), it is possible to ascertain the precise point at which the valve
+opens. Next pull round till the crank is in the position for the air
+valve opening, and observe that it is set correctly. Then go on to a
+trifle above the back centre, where the exhaust valve should close, and
+so on till the opening and closing of each valve has been checked. It
+will be noticed that the air, and sometimes the gas, valve opens before
+the exhaust closes. This overlap is necessary; and it will be found that
+the smaller the engine and the higher the speed the greater this overlap
+will be to obtain good results, although a good deal of individual
+judgment must be used in settling the exact amount of overlap, as the
+requisite amount may, to get the best results, vary in different engines
+of precisely the same dimensions and type.
+
+When dealing with engines which have no separate gas valve--the gas
+being admitted with the air, which is sometimes the case with very small
+engines--the above notes referring to the gas setting independently,
+will, of course, not hold good.
+
+It may be mentioned with regard to the lump on the opening side of the
+exhaust cam, that this if overdone is found to be detrimental on large
+engines, and even on small ones. If it is too large, it will cause both
+exhaust valve and seat to become burnt and pitted, due to the surface
+being exposed to the exceedingly high temperature of the expanding
+gases. If it is too large, it is equivalent to opening the exhaust valve
+too early, and the effect is the same, viz., a waste of power and damage
+to the valve and its seat.
+
+[Illustration: FIG. 43.]
+
+[Illustration: FIG. 44.--Brake Testing.]
+
+The method of grinding in the valves to their seats with emery powder
+and oil is so well known that no further description is needed here. We
+give, however, in fig. 43 a sketch showing a very expeditious way of
+dealing with very badly worn or burnt seats. The sketch explains itself.
+Such a tool is readily made; even the cutter could be turned and filed
+up to shape and then hardened at home. By lightly tapping in the taper
+cotter pin little by little, sufficient pressure is put on the cutter to
+make it an easy matter to completely re-face an old seat or form a new
+one. A T-wrench or "tommy" can be used to work the cutter spindle. The
+lower part of the latter must be the same diameter as the existing valve
+spindle; the bush acts as a guide; and as the bevel of the cutter
+should be the same as that of the valve, a very little grinding in with
+emery powder is required to finish the job off.
+
+In fig. 44 we give a diagram showing the method of testing for Brake
+H.P. of engine, as it is frequently interesting to make such a simple
+test after any alterations or adjustments have been made.
+
+Two spring balances and a rope or cord (according to the size of the
+engine), fitted with a few wood blocks as shown in section, fig. 44, to
+keep the rope on the rim of fly-wheel, is all that is required for this
+test. The following formula may be used for arriving at the B.H.P.:--
+
+  B.H.P. = (S1 - S2) 3.14 x D x R / 33000
+
+  S1 = Reading in lbs. of spring balance No. 1.
+  S2 = Reading in lbs. of spring balance No. 2.
+  D =  Diameter of fly-wheel and diameter of brake
+       rope in feet.
+  R =  Revolutions of fly-wheel per minute.
+
+  As 3.14 x D / 33000 will always remain the same for any given engine and
+  gear, we may call that expression C; then the B.H.P. may be written--
+
+  B.H.P. = (S1 - S2) C R
+
+
+
+
+CHAPTER VIII
+
+OIL ENGINES
+
+
+The small oil engine is practically the same as the gas engine, with the
+addition of a vaporiser for converting the oil into gas, or vapour, to
+be exploded in the cylinder; consequently the one may be converted into
+the other in many cases without much trouble. The difficulty of
+producing an efficient oil engine lies principally in devising a
+satisfactory and reliable vapouriser--one which will work equally well
+under all loads. The heat supplied to the chamber must be sufficient to
+vaporise the oil, but not great enough to decompose it. There are
+various methods of vaporising the oil, and many types of vaporisers are
+employed to attain the same end. There are some in which a charge of oil
+is drawn by suction into a hot chamber in which it is converted into
+vapour and at the same time mixed with a small quantity of hot air; this
+rich mixture is then passed into the combustion chamber of the engine,
+in the same manner as coal-gas would be, where it is further diluted
+with more air drawn in through the air valve. Other arrangements cause
+a jet of oil to be injected into a chamber containing hot air, in the
+form of spray, which immediately converts the oil into vapour, and is
+then passed into the cylinder, compressed, and fired. Then, again, we
+can pump oil through a spraying nipple into the vapouriser (which is
+kept at a suitable temperature) whilst the cylinder is being filled with
+air on the suction stroke. On the following compression stroke the air
+is driven into the vapouriser, which communicates with the cylinder
+through a narrow neck, and mixes intimately with the oil vapour.
+Gradually, as the pressure rises, due to compression, the charge becomes
+more and more explosive, until at the completion of this stroke it has
+attained the proper proportions of air and oil vapour, and is fired by
+the temperature of the vapouriser and that caused by a high compression;
+that is, the charge is fired automatically; and once the engine is
+running, no heating lamp is required to keep the vapouriser at the
+correct temperature. It is necessary, however, to raise it to the
+workable temperature at starting. This is known as the Hornsby-Akroyd
+method.
+
+Capel's arrangement is also simple and efficient, and has the additional
+advantage of being capable of being fitted to their existing gas
+engines, the conversion being made in a very short time. This vapouriser
+consists primarily of a tubular casting A, on the outside of which are
+formed a series of vertical ribs, shown in plan, fig. 46, running to
+within a short distance of the flange at one end, as shown in the
+section, fig. 45, thus providing an annular space C between the upper
+ends of the ribs and the flange. This casting is enclosed by an outer
+casing B, which fits well over the inner tube. It has also a number of
+small holes drilled near the lower end communicating with the channels
+between the ribs. Thus it will be seen that when the gas valve is opened
+and suction takes place, air is drawn in through these holes, passes up
+into the annular space C below the top flange, from there travels to the
+opposite side of vapouriser, and mixes with the oil which is also being
+drawn in through a small nipper at N, fig. 45. Both then pass between a
+series of pegs, where they become thoroughly mixed, and finally pass on
+to the inlet valve V, fig. 47, and so into the cylinder, where the
+complete charge is mixed up and compressed and fired in the usual
+manner. Iron ignition tubes may be used, and one heating lamp serves a
+double purpose in keeping the tube and vapouriser hot at the same time.
+This lamp is fed by means of a pump actuated from the side shaft. The
+plunger of the pump is loaded with a spiral spring, which may be
+adjusted to give any desired pressure, and is kept constant and steady
+by means of an air vessel. This pump is shown in fig. 48. It is actuated
+by means of a rod and lever from the side shaft of engine. The plunger P
+works in a barrel B, which is carried by a small reservoir R, the latter
+being in communication with the main oil tank by means of the pipe H.
+
+[Illustration: FIG. 46.]
+
+[Illustration: FIG. 45.]
+
+[Illustration: FIG. 47.]
+
+[Illustration: FIG. 48.]
+
+[Illustration: FIG. 49.]
+
+[Illustration: FIG. 50.]
+
+[Illustration: FIG. 51.]
+
+The plunger is loaded with a spiral spring, and has a ball valve, as
+shown. Intermediate between this small reservoir and the main oil tank
+is another set of valves, shown in fig. 49. It will be seen that the
+suction of the pump will draw the oil up, the small and lower ball
+valve, of course, allowing it to pass freely. On the down stroke the
+lower valve will be automatically closed, and the oil will be put under
+pressure, this being determined by the load on the plunger valve, which
+is adjustable by means of the screw S, fig. 48. When the required
+pressure in the pipe P, figs. 45 and 49, has been attained, the plunger
+valve lifts on each stroke and the surplus oil flows through the plunger
+into the small reservoir R. The latter is at about the same level as
+another still smaller reservoir M (shown in figs. 47 and 50), a flow of
+oil being established between the two by means of a pipe Q (see figs. 48
+and 50). In the reservoir R is fitted an overflow pipe, so that the oil
+cannot rise beyond a certain level; hence the head of oil in the smaller
+one M is always constant. On the suction stroke a partial vacuum is
+formed in the engine cylinder, consequently the pressure in the
+vapouriser drops somewhat below that of the atmosphere, and this small
+difference in pressure is enough to cause the oil to rise in the small
+passage X, fig. 45, beyond its normal level, and overflow into the
+vapourising chamber, as previously described. The valve or nipper N is
+shown open in the diagram, fig. 45, and all that is required to stop the
+engine when running is to drop the small handle L, fig. 45, when the
+valve will close, due to the spring S. The air vessel shown in fig. 49
+is in communication with the pipe leading to the blow lamp. A pressure
+gauge can also be fitted, although it is not in any way a necessity.
+
+The ratchet wheel and pawl shown in fig. 48 are part of the lubricator.
+The wheel drives a brass or gun-metal plug, producing an intermittent
+rotary motion. The plug has a small hole in its periphery, which becomes
+filled with oil when it is at the upper part of its travel, and empties
+the oil out into a discharge pipe T, when it is inverted, and is then
+led away and applied to the piston at the required spot. Fig. 51 shows
+this arrangement in section.
+
+
+
+
+
+End of the Project Gutenberg EBook of Gas and Oil Engines, Simply Explained, by
+Walter C. Runciman
+
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