rr PETROL ENGINE TOPICS A 15-c.c. FOUR-CYLINDER ENGINE

L as 1art By Edgar T. Westbury by just S a result of my article on “ Multi-cylinder engineering. One might just as well ask why and Developments” in the issue of December any elaboration or refinement, beyond that lots A 12th, I have received many comments from required for sheer utility, should be introduced Lent readers on this subject. In a few cases, it is into any kind of model engine. The answer is ers. considered a questionable policy to introduce any that the engine is something more than a means of complication into design, unless it can be shown to an end, it is a worthy end in itself, and every han that this will result in greater utility, or higher item in its design or equipment adds to the performance. Why use a number of cylinders, pleasure of its construction, and the ultimate ack when one will do the job just as well ? pride of achievement. For this reason, the The Here we have an instance of the attitude to development of the multi-cylinder engine is worthy 2) which I have already referred in earlier articles, of encouragement, so long as it does not become namely, the inability to consider any aspect of an obsession which eclipses or side-tracks the ht ; the model petrol engine except its function as a equally important considerations of efficiency and the power unit, in other words, a mere means to an compactness, in which the simpler single-cylinder ont end. Granting that this aspect is a highly import- engine is at present supreme. wn. ant one, and indeed paramount in many of the Objectors to the development of the “ multi,” suit applications of the model petrol engine-which, however, are very definitely in the minority, and der I may add, never have been or will be neglected most of my readers have expressed a very ont in Petrol Engine Topics, it is certainly by no emphatic desire for further information on this ne. means the only aspect worth while in model subject. The mere hint that I am working on the ! of :nt, :E llar : it- 1lly

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Fig. I. General arrangement of the “ (1) Main cylinder and crankcase block : (2) Cylinder-head :(3) Cylinder jacket cover : (4) Sump : (5) Main bearing Housing : (6) Timing-ge (13) Connecting-rod : (14) Crankshaft : (15) Camshaft : (16) Gudgean-pin : (17) Tappet guide (18) : 198 FEBRUARY 6, 1947

ngement of the “Seal” 15 c.c. engine Housing : (6) Timing-gear housing : (7) Timing cover : (8) Valve cover ; (9) Flywheel ; (10) Cylinder liner : (11)Valve liner : (12) Piston : Tappet guide :(18) Valve : (19) Timing pinions : (20) Timing spur gear : (21) Breather : (22) Oil trough. 199 T THE MODEL ENGINEER FEBRUARY 6. 1947 development of a multi-cylinder engine myself This is not an exaggerated picture ; I have m has been sufficient to arouse a clamour for the seen it in many otherwise excellent model power- a! drawings of the engine, and I find that readers boats, both in regattas and exhibitions. It is an h are not content to-wait for the indefinite time object lesson on where the utilitarian creed (“ If ti necessary for me to complete the development it does the job, it’s O.K.! “) is liable to lead us n work on the design. eventually. I offer no criticism of those who, for The engine in question, general arrangement want of a more appropriate power unit, have been u drawings of which are shown on pages 198 and 199 compelled to use the only available means of tl is a “ straight four,”water-cooled, side-valve en- motive power, but I do say that it is not good P gine of 15 cc., on which I have been working for model engineering, and that there is a very strong ej quite a long time now, and a good deal of prac- case for the introduction of engines which are in ti tical work has been put into construction and harmonv with their environment. ri development, with the aid of several friends who It may, perhaps, be objected that the design of s! are keenly interested in the project. It is my the “ Seal ” engine illustrated here is more in 0 intention to produce designs for engines of keeping with automobile than marine practice. C; both 15 c.c. and 30 c.c., and equipped with That is perfectly correct, and the reason is c: either side or overhead valves, but as the because the former lends itself more readily to fc smaller size of engine is the more exacting, simple and straightforward methods of construc- v it has been selected as the one to be tackled first. tion ; but it is also true to say that automobile SI There have been quite a few delays and hold- engine design has been used as a basis for some a# ups in the progress of this work, but to reassure of the most successful light marine engines, and U readers who may have any misgivings on this in modern motor craft, conversions or adaptations tc point, I would mention that these have been of automobile engines are becoming increasingly P concerned with ways and means of production popular. Even for models of the larger types of rather than design ; questions of the availability boats, such as tugs. coasters or even motor liners. il of correct materials, machining methods, and the prototypes of which have much more special: a delicate problems of patternmaking, of moulding. ised types of engines, the four-cylinder engine is 0 have caused quite a few headache; These snags by no means so blatantly discordant as a single, a have gradually been ironed out, and I hope to be and moreover, fits in much better with the a able to show readers alternative methods of available space and shape of the engine-room. n construction to cope with such difficulties as Should the occasion demand. there is no reason P they may encounter in these respects. As to the why two, or even more, engines of this type t: success of the engine, when built correctly to the should not be installed. a design, I am in no doubt whatever, as sufficient Most of the multi-cylinder engines so far C experience has been obtained in experimental produced have been too large for installation in n work to ensure that the engine will work according hulls of the size popular among model power-boat V to plan. enthusiasts. Large boats are not only unwieldy t and expensive to build, but an even more serious i The Object of the Design objection is the difficulty of transporting them. Although, as already pointed out, one does not I know of one stout fellow who habitually carries really need an excuse to build an interesting type around a 6-ft. boat, but he is by no means : popular on crowded ‘buses and trams with this f of model engine, I may mention that the design a has been produced for a definite purpose ; but strange cargo, and even on the railways, it has on its application is by no means confined thereto. more than one occasion been something of a It has long been my intention to provide a really “ white elephant.” The “ Seal ” engine is i suitable for installation in a metre boat. without suitable power unit for model prototype boats, d and in particular, those of the launch or cruiser being either too heavy? or out of proportion in type, which are deservedly popular in regatta respect of bulk ;and its power output is ample events, such as nomination and steering com- for the requirements of any craft of this size, petitions. Of the many boats of this tvpe in other than thoseintended for racing on the existence,a very large proportion are now circular course. equipped with petrol engines ; but while the This, then? is the primary raison d’etre of the latter may be quite satisfactory in performance “ Seal ” engme, but it is also quite suitable for and reliability, few of them are of a really appropri- other purposes, such as installation in a scale type, in respect of design and character, for model motor-car (other than a racer), a model marine installation. locomotive, or even for stationary work such as How often does one find, after inspecting the driving a portable generating set. exterior of a model boat on which every loving care has been bestowed to get all details correct Adaptability and complete, and to preserve the true nautical It is quite in keeping with the spirit and “ atmosphere,”that all illusions are shattered on tradition of model engineering that no two con- looking down the engine-room hatch ! Without structors require or prefer quite the same thing ; casting any aspersions on the usual commercial individuality both in thought and effort is an type of petrol engine, the sight of it in a ship’s essential factor in the make-up of the successful engine-room gives one quite a shock, and is model engineer. In all my designs of engines often rendered worse when its shortcomings for produced in recent years, I have recognised this the particular purpose are imperfectly remedied fact, and have allowed for the possible deviations by the addition of a crudely-made cooling fan, or which constructors may wish to make from the a tin water-jacket and a yard or two of rubber set design. Not only are several of the minor “ plumbing.” features of the design optional, but the arrange- 233 47 THE MODEL ENGINEER FEBRUARY 6, 1947 ment of the main components can also be modified alone, in the course of which many major and re as required. This ability to “ ring the changes ” minor parts of the design have been successively r- has proved to be one of the most popular attrac- evolved and ruthlessly scrapped. An even greater tions in several engine designs, and is by no task than that involved in the technical problems r”f means lacking in the present example. of design has been the solution of the machining IS Thus the main casting can be turned either problems, each one of which has been individually lr way round, so as to bring-the valve gear on either tackled, with due regard to the equipment which n the port or starboard side ; this entails making the average model engineer will have available to If provision for the attachment of the timing gear to carry it out. The result, I dare venture to assert, ii either end of the engine, the castings for the is fairly satisfactory from most practical points of B timing case and bearing endplate being “handed” view, and although I cannot hope that the design a right or left as required. The water circulating will satisfy all my critics, I have little doubt of its system may be arranged so that the water enters general popularity. or leaves the jacket at either end, this again A word of caution to those ambitious construc- calling for right- or left-handed castings for the tors who are itching to get going on an advanced cylinder head cover plate. These optional design of engine : don’t start building this engine features may not be of very great importance until you have weighed up all the difficulties when only one engine is to be installed, and no involved, and are quite confident of your ability serious restrictions of space exist, or exact to carry out all the work to the exacting degree of adherence to a set arrangement has to be complied precision required. Theoretically, it is no more with ; but they are important when engines have difficult to build a four-cylinder engine than a to be used in pairs, to drive contra-rotating single of the same bore and stroke, the only propellers. difference being the quantity of work involved ; The auxiliary engine fittings such as manifolds, but in practice, the success of a “ multi ” depends ignition gear, carburettor, water and oil pumps, not only on the individual units, but also on their are not illustrated in Fig. I, but it may be proper co-ordination. I do not underestimate observed that these have been fully worked out, either the ability or the perseverance of my and give equal scope for versatility in detail or readers, and I know from experience that even arrangement. A combined induction and exhaust raw beginners are capable of overcoming the most manifold has been designed, and is shown in formidable difficulties in construction, with position in the photographs. The ignition dis- totally inadequate equipment, at that ; but it is tributor is fitted on the timing end of the engine, sometimes difficult to get the beginner to realise and may be driven directly off the end of the just how big a job he is taking on. I have often camshaft, as in the “ 1831 ” engine ; but, for been criticised for making things seem very marine work, it is considered preferable to pro- difficult, but an ever-increasing number of readers vide a vertical fitting, the shaft being geared to are finding out that my policy of putting them on the camshaft, and extended downwards to drive their guard about the difficulties and pitfalls a water circulating pump. Either gravity or ahead is better than pretending the latter do not forced lubrication is provided for, the former exist. Quite a few people have thought that being quite reliable for normal work. A simple building small petrol engines was child’s play- form of automatic carburettor, which will give a until they tried it ! There are a few haphazard full range of speed control on the throttle lever workers who have enjoyed beginner’s luck, but only, has been designed for this engine, and most of us find that the best and most careful although not specified in the standard design, the work we can do is not too good for this class of possibility of equipping the engine with magneto model construction. But as in other things in ignition has not been lost sight of, and will be life, difficulties exist not to be dreaded, but to be dealt with in an appropriate manner. overcome ;and if there is any reader who is It will be clear to most readers that the scheming scared away from a job just because he is warned out of a design to provide such complete equip- of its difficulty, all I can say is that he would ment, and so many alternative features, has not never have made a really successful model been a five-minute job, but has taken up several engineer in any case. months of spare-time work on the drawing board (To be continued)

A Lathe Tailstock Tool Holder (Continued from page 196) moved around its axis so as to present the tool machine, well under size below bottom thread to the work at any convenient angle. One cutter diameter. Since no tap with such a diameter will, of course, be set forward of the other and a fine. thread will be likely to be available, and the shape of the cutters will be such as to the thread must be screw-cut in the lathe. give two diameters at the same time on the end Bolt body A (by the tool-post slots already of the stock.The cutters are fed up by the tail- formed) to an angle-plate bolted to the lathe stock hand wheel.The stock is fed through as it face-plate ;centre to the drilled hole, turn out is used by slacking the headstock mandrel chuck. parallel to bottom, thread diameter and then A cutting-off tool in the cross-slide will cut screw-cut the thread to fit the plug B. the job off when completed. When setting up, the plug B should be driven The ho!e in the back of the body A (screwed very tight, by a hammer, into the tailstock internally to take the screwed end of the taper barrel. It can be removed, as would a work on B) must be drilled first under the drilling centre, by rotation of the hand wheel. 201 PETROL ENGINE TOPICS * A 15-c.c. FOUR-CYLINDER ENGINE By Edgar T. Westbury

VERY important factor in the success of odd-angle machining operations have been A an engine of this type is the quality of the avoided wherever possible-in fact, they are castings used in its construction, the only introduced in components or surfaces accuracy and detail of which need to be of a which are not essential to mechanical accuracy, high order. Both the pattern-making and so that small angular errors in these operations moulding on these castings have called for great do not affect the working of the engine. The skill; and in the former work, I have been small screws and bolts used in the engine are extremely fortunate in obtaining the co-operation mostly in B.A. sizes, as these are generally the of Mr. H. C. W. Frost, who is known to many most readily available, and offer the widest readers of THE MODEL ENGINEER for his crafts- choice of sizes ; but there is no objection to the manship in making small and intricate patterns, use of the nearest Whitworth sizes, and these some of which have formed the basis of notable offer advantages for threads which are tapped exhibition models. The castings have also in the light alloy castings. Positions of clearing been produced by a craftsman of no mean ability, holes are shown on the drawings, but as the and I hope to be able to make an announcement tapping holes, in practically all cases, can be that they will be available to readers in the near produced by“ following through ” from these future. holes, there is no necessity to show these in detail. Construction All the castings of the engine have been Part No. I.-Main Cylinder and Crankcase designed so that they can be machined by the Block equipment and methods available to the average This is the largest single component, consisting model engineer; the largest casting will swing of a cored casting incorporating seatings for the comfortably in a 3-1/2in. lathe, and even with “wet ” cylinder liners, housings for the main smaller lathes, alternative methods can be devised bearing end-plates, and surfaces for the attach- for handling the essential machining operations. attachment of the cylinder head block and sump. Much of the work on the castings can be done It will be noted from Fig. 2 that all the main by mounting on a faceplate or angle plate, and machined surfaces are at right angles to each other, so that setting-up is simplified, and various *Continued from page 201, “ M.E.,” February alternative machining methods can be employed. 6, 1947. The casting should first be set on a surface plate

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.; In. t0 r, I :r :o 1S ct ie I Main structural castings of the ” Seal” 15-c.c. engine 279 THE MODEL ENGINEER MARCH 6, 1947 and checked up as to general dimensions ; it displacement of cores or misalignment of mould- is not necessary to attempt complete marking-off, ing boxes, are “halved out.” Do not forget so long as it is ascertained that all essential sur- the invariable rule to take location from surfaces faces will machine up in their correct location which will not be machined, as the amount of and relation, and any possible small errors of allowance left on machined surfaces may vary dimensions, such as may be caused by slight slightly, or may be affected in the fettling process.

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XEe Fig. 2. Sectional side elevation and plan of cylinder and crankcase block the 280 THE MODEL ENGINEER MARCH 6, 1947 The machined surfaces on this casting are in- squareness, by reference to the preliminary dicated by the customary mark (f). Do not, check-up, is preserved, and machining to a at this stage, plug the cylinder seating bores for distance of 3/4 in. to the shaft centre line. This marking the centres, as it is more convenient dimension is not a critical one-the really essen-

MACH!NED FACING EXTENDED As SHOWN DOTTED IN END ELEVATION AT KK (BOTH ENDS)

Fig 3. Sectional end elevation of block

to do this at a later stage. tial thing is that the surface should be parallel The general checking-up of casting dimensions to the shaft axis, and square with the cylinder is one of the first things any constructor should bores-but getting it right in the first place do, as it brings to light any possible errors or will simplify subsequent setting up for other discrepancies either in the drawings or castings, operations. Leave the machined surface as and gives one an opportunity to invoke the aid clean and smooth as possible, as it is required of “ the gentle art of cornpromise ” in putting to make an oil-tight joint eventually. them right if it should be necessary. If this For machining the head, it is best to bolt the rule were universally observed, we should en- base to the lathe faceplate, because assuming counter much fewer complaints about castings that the latter runs truly, the parallelism of the which won’t clean up, or structures which top and bottom surfaces will then be beyond machine up too thin for proper strength. Even dispute. A simple way to hold the casting is to in the best regulated designs, and the most pass a flat bar right through the end-plate hous- carefully made castings, errors are sometimes ings, with a couple of bolts as near as possible inevitable, and the common policy of “leaving to the ends of the casting, so that they are easy plenty of metal ”on machining surfaces is of access and provide maximum security. quite a fallacious one, since it encourages slip- Incidentally, I have often been criticised for the shod setting-up, and consequent risk of false rela- use of any odd bits of junk for use in bolting tion between machined and unmachined surfaces. work for machining-not at all like the neat Although there are several quite practical straps and clamps so often seen in the text-book methods of procedure in machining this casting, illustrations. Well, I am all for using the proper the recommended method is first to machine fittings for the job whenever they are available ; off the top and bottom surfaces, and use one or and if a great deal of use is made of any kind other of these as a reference surface for subse- of fitting, it is worth while to spend any amount quent operations. The casting may be held in of pains to make it not only neat and workmanlike, the four-jaw chuck, by the head end, for facing but also thoroughly well adapted to its job. But the bottom surface, setting up so that general the requirements of machining problems in the 281 THE MODEL ENGINEER MARCH 6. 1947 TH amateur workshops are so many and varied that rest being merely a clearance hole cored integral one would require a complete arsenal of special with the inside of the casting. Whether the fittings to cope with all eventualities. One should end-plate housings are bored on the faceplate not place an undue importance on the fittings or on the cross-slide, the camshaft tunnel is themselves-they are purely and simple a most suitably dealt with by setting the casting means to an end, and may possibly only have over the required amount. It is easy to do this to be used once, or at most, very rarely. For in the former case, simply by swinging the angle this reason, the use of “rag-time ” clamping plate bodily on the faceplate, and this ensures devices is fully justified, providing that they true parallelism of the two bores. If the boring serve their purpose with reasonable efficiency, is done on the cross-slide, however, it must be and do not involve any loss of quality in the work completely re-set, and the packing under the produced. base reduced bv a thickness eaual to the vertical The truth and smoothness of the finished ton height of the camshaft above- the main centre, surface is of even greater importance than that namely, 23/32 in.Care must be taken to ensure of the bottom. but it mav be found a sound that the casting is re-set truly in line with the policy not to machine it right off to finished lathe centres and the use of an alignment bar dimensions 2-1/4in. from the centre line of shaft or mandrel through the bore of the housings or 3 in. from the base surface-but to allow for would be useful in this respect. The vertical a finishing cut after the liners are inserted. and horizontal offset measurements from the Next, the ends of the casting should be faced, camshaft to the main centre are not highly and the end-plate housings bored. If a fair- critical, as the meshing of the gears can be sized angle plate can be swung on the lathe adjusted by the position of the idler gear, but it is k faceplate, the casting may be set on this, securing best to get them as accurate as possible, on it by clamps or straps over the feet of the bearers. the general principle that good work is easier Check the general squareness of the casting by than bad, because it cuts out the necessity means of a try-square on each side, then shift for subsequent “botching” to correct earlier the angle plate to centre the housings-do not mistakes. rely on the cored holes for setting up, but work from essential dimensions, and if any doubt exists as to the correct centre line, plug the bore Boring Cylinder Seatings at one end with a piece of hardwood or metal, This is a highly important oneration, as the t and set out the centre on it. dimensions, squareness and location of the bores shi If it is found difficult or impracticable to swing must all be correct. The cored holes should hoi the casting in the lathe, it may be clamped to be plugged and the centre line of each very a& the cross-slide, packed up to centre height, and carefully marked, but once the first bore has by bored with a boring.bar.This method has some been located, it is easier and generally more fro definite advantages, especially in positive loca- accurate to locate the others by measurement. lot tion of the centre line ; if the exact height of If the lathe will swine the casting at maximum bm the lathe centres, over the cross-slide, is known eccentricity, that is, when boring either end l$ or ascertained. the reauired thickness of nackinn seating, it may be bolted to the faceplate, using can also be found, and parallel blocks or strips the same means as before, but in this case, some use built up to this thickness. Use the try-square measures are necessary to avoid damaging the against the lathe faceplate to check the squareness finished bores of the housings. A piece of soft E of the casting, and secure it by clamps over the wood packing under each end of the strap will serve this purpose. Before mounting the casting, EZ bearers as previously suggested. the The housings are bored to 1-1/8in. diameter, however, one side of the casting, at the base, and if it is found difficult to adjust the boring should be filed straight, and parallel with the 1Oa bar to finish exactly to size, it may be noted centre line, to make contact with an alignment alij strip for use in locating the bores. COI that this, again, is not a critical dimension? as the the external diameter of the bearing housmgs Having lightly attached the casting to the face- plate, set it so that one of the bore-centres runs the can be adjusted to fit. Facing the end surfaces du is best carried out by swinging the castings on a dead truly, and tighten the bolts holding it in place. Before proceeding further. clamp the SUI mandrel, for although it is practicable to do em this bv means of right- and left-hand facing alignment strip (any piece of bar or strip material cutters-in the boring bar, the result often leaves having a dead straight edge) to the faceplate, in much to be desired.The use of a point facing- in contact with the prepared side of the casting. axi tool, in conjunction with traversing movement The bore may now be machined to size, using-a stiff boring tool and taking care to ensure parallel- a of the work on the cross-slide, is practicable, tht if one is quite certain that the cross-slide moves ism, or rather equal diameter of the upper and lower seatings. At all costs, tapering “the mc exactly at right angles to the lathe centres- bo which is by no means to be taken for granted wrong way “larger at the lower seating- must be avoided. If a reamer or sizing cutter CZII in all cases. an; At the same setting as the facing of the ends, is available it may be used to finish the bores to ensure uniformity of size, but it should not tht a cut can be taken over the flanges on the upper wi part of the casting. These stand 1/16 in. proud take out more than about two or three thousandths of an inch on the diameter. The counterbore thr of the end face, but this measurement is not L tht important. at the top end is of course machined at the same setting, and if any metal has been left on the top mt joint face for final machining, this should be SUI Camshaft Tunnel allowed for in assessing the depth of the counter- en This requires only boring at the two ends, the bore. is 282 THE MODEL ENGINEER MARCH 6, 1947

2 uniform in size and 3te exactly parallel ; a sec- is ond cutter may be mounted in the bar, if ng YliS desired, to machine the :le counterbore at the yes same setting. As it is impossible to run the 3 bar between centres, he the overhung cutter :a1 may spring to some re, extent, so it is advis- Ire able to take several he traverses through each lar bore, with a slow feed, to eliminate any pos- 3 sible errors from this source. Saddle boring :; should always be done be with the cross-slide is locked or very stiffly cm adjusted, and the ier saddle gibs set so that they allow no percep- !ty ier tible shake. Valve Ports Firstoperation on block : facing sump joint surface The setting up and machining of these he After machining one bore, the casting must be may be carried out on similar principles to that of shifted exactly the centre distance to the next the cylinder seatings, with the difference, how- E: bore (7/8 in.), keeping it in close contact with the ever, that they are drilled from solid metal. One rY aligning strip. The distance may be measured point which must be carefully watched is the as by any convenient means, such as a depth gauge tendency of the drill, after breaking out into re from the edge of the faceplate, or it may be the cored recess, to run out of truth when starting located by reference to the marked-out centre, to work on the lower part of the hole. This F but for positive accuracy there is nothing to can be avoided by drilling the upper part under- Id beat the use of a slip gauge and stop piece. A size, and then using a stiff pilot drill, a tight 1g disc of metal exactly 7/8in. diameter may be fit in the hole, to start the lower part. The drill le used as the gauge, which is placed in contact may be made from silver-steel, flattened and le with the end face of the work (while in its original diamond-pointed at the extreme end only, and 1ft location) and the stop piece clamped to the face- it should be lubricated on the shank to avoid ill plate, so that the gauge is just free to move in risk of seizing in the pilot bore. As there are g¶ between the two without shake. The gauge-is (Continued on page 285) #e, then removed, the work le loosened, and slid along the nt alignment strip until it makes contact with the stop piece, e- then re-bolted for machining IS the next bore. This proce- in dure is repeated for locating le subsequent bores, and will al ensure that they are all dead e, in line, equally spaced, and g. axially parallel. For machining the bores on 1”- a lathe too small to swing zr the casting, the latter may be Le mounted on an angle plate bolted to the cross-slide, due :r care being taken to set the :s angle plate dead square with X the lathe centres, or parallel 1s with the faceplate, which is .e the same thing. After locating Le the first bore, the same P methods of relocating for be subsequent bores may be *- employed. If a set boring bar is used, all bores will be Boring the endplate housings with a boring bar between centres THE MODEL ENGINEER MARCH 6. 1947 STEAM VALVE FILLER PLUG SAFETY VALVE STEAM DRUM

GENERAL ARRANCEMENT OF BOILER filling of which lasts for fifty minutes under spring may be lifted to ensure that the ball is not normal conditions. sticking. The superheater, which is placed between the The boiler is housed in an asbestos-lined water drums, consists of two parallel 5/16-in. bore steel case, being suspended from the top copper tubes fitted with a return bend, as per by four screws,the nuts of which can be “ L B S.C.” The whole of the boiler is brazed. seen in the photograph, brazed on to the water The fittings consist of a safety-valve, set to drums. blow off at 35 lb./sq. in., fitted with stainless-steel The firing is by coal gas fed into a gas-ring ball and spring, and a steam-valve so constructed type burner, the air hole of which is on the other that its stainless-steel spindle cannot be screwed side of the tube in the picture and is non- out, a requirement which considerably com- adjustable. The gas tap is fitted with a bypass to plicates construction but is desirable, considering prevent the burner being accidentally turned out the age of the recipient, which also ruled out the and to provide sufficient for average running. fitting of a water gauge whose glass might easily When first tested, it was found that water from be broken. A pressure gauge was similarly the exhaust, which is led up the chimney, thought to be an unnecessary refinement. extinguished some of the gas jets immediately Since the photograph was taken a lever has below. This was overcome by fitting a small been added to the safety-valve in order that the stainless-steel baffle plate set at an angle, as shown. Petrol Engine Topics (Continued from page 283) eight ports to drill, the making of a simple tool strap and bolts may again be used to secure it, of this kind is worth while. The holes should with the wooden pads to avoid marking the be opened out and reamered,. the lower part housings ;the latter allow of a rocking or “ self- being 1/4 in. diameter, and the upper part 5/16 in., aligning ” motion, so that a good bearing of the with a counterbore 3/8 in. dia. by 1/16 in. deep. strap is obtained. Centre the boss of the breather as 1, It is quite practicable to machine these ports exactly as possible, then face the top surface, drill IS in the drilling machine if great care is taken truly and tap or screwcut to 7/16-in. fine thread. .e in locating the centres, and keen, true running Other machining operations on this casting d drills are used. A special sizing and counter- are quite simple and obvious. The side face boring cutter may be made for finishing. the of the valve chamber is best machined by face bore. But generally speaking, more positive milling, which may be done by bolting it on the accuracy is obtained by machimng them in the cross-slide and using a fly-cutter in the lathe :, lathe, with proper means of setting up or locating, chuck. Mark out the cross holes for the valve 0 as already described. passages exactly in line with the vertical ports ; 1. but it is advisable to defer the drilling of them Breather Orifice until the valve liners are inserted. t It will be seen that the centre line of this is The undersides of the bearers should be milled 1. set at an angle of 20 degrees to the vertical, if possible, and the best way to do this is by e the exact angle not being critical, and the best mounting the casting on a vertical slide and using e way to machine it, in the absence of an adjustable an end mill. The surface should be exactly angle plate, is to plane up a piece of wood to the level with the shaft centre line, to facilitate lining .S required angle, and use this as a packing piece up when the engine is installed. v tn mount the canting on the faceplate. The (To be continued) e 285 s in was the PETROL ENGINE TOPICS sual ter- ine, * A 15-c.c. FOUR-CYLINDER ENGINE the ling By Edgar T. Westbury :ure :ach :ach HE flat joint surfaces on the main block and finds that there may be, and often is, a great was T other castings, which form oil, water or difference between “ finish ” and accuracy. The gas seals, are intended to be finished form of tool which I have found most suitable fine eventually by lapping, as this is the simplest for finishing joint surfaces is either a narrow tker way to ensure the smoothness and accuracy round-nosed tool or an obtuse vee tool with the ded necessary to obtain a reliable seal. In machining, angle just slightly rounded ; in either case, the ica- however, no pains should be spared to finish these edge should be oilstoned to a high finish. As there is a good deal of surfacing work to do lere on the castings of this engine, it will 3ne pay to make a special tool for the job ; ,ooo it should be kept in keen condition aion and only used for a light final cut. ler- heir Cylinder-head Block (Fig. 4) ate, Both the upper and lower surfaces AS of this casting are joint surfaces, the as a former being just a low-pressure and water joint, while the latter is required an to hold cylinder pressure and there- fore calls for the most careful fitting. t of The casting may be held in the four- rich jaw chuck for machining each surface hip in turn, care being taken to get them no- parallel with each other.The inclined :ern side edge in which the sparking plugs me. are fitted may be machined by clamp- >del ing the casting to the side of a block ldel of wood planed to an angle of 30 IOW degrees and mounting this on the ‘the lathe faceplate. While the head is ine. still attached to the wooden block, the positions of the sparking plugs may be marked off, and each in Block set up for face- milling valve cover and manifold joint surface

surfaces as smoothly and accurately as possible, to reduce the time and trouble of the lapping operations. Incidentally, one soon finds out faults or inaccuracies in the lathe mandrel or slides as soon as one starts to lap machined surfaces, as the high spots are shown up immediately, and apart from inconsist- ent errors due to blunt or unsuitable tools, or irregular feed, it indi- cates the location and nature of the faults in i-ii the lathe. One soon td. *Continued from page 285, ” M.E.,” March 6, Boring the cylinder seatings-note the use of the aligning strip to facilitate 1947. re-setting for subsequent bores THE MODEL ENGINEER

Cylinder-head

SECTION A.A. Fig. 5. Cylin

342 MARCH 20, 1947

UNDERSIDE To TION HEAD

Cylinder-head block

Fig. 6. Sump

6- ~; HOLES; I~~ P-C~. 1 II. SECTION B B

Fig. 5. Cylinder-head cover plate i L THE MODEL ENGINEER MARCH 20, 1947 turn accurately centred on the faceplate for It will be seen from the general arrangement drilling and tapping the holes. This will drawing on pages 198 and 199 of the February ensure that the plugs are all at exactly the same 6, 1947 issue that an oil trough is fitted inside the angle, and accurately seated when screwed home ; sump, being held in place by two countersunk it is a much more reliable method than drilling screws through the bottom of the latter. The the holes in a drilling machine and facing them holes for these screws are not shown in the detail with a pin drill. drawing, as it will be found most convenient to mark them out when fitting the trough. A very Cylinder-head Cover Plate (Fig. 5) small machining or filing allowance has been left This is available with water outlet facing in on the end faces of the sump, as one or other of either direction, to suit engine arrangement, and these will have to be faced to form a seating for requires only to be faced on the under surface, either the oil or water circulating pump, if fitted. which is easily done by holding it in the four-jaw chuck. The hole for the water outlet is drilled at Valve Cover (Fig. 7) an angle of 10 degrees to this surface (drilling This is an optional fitting, as some constructors machine methods are quite in order for this) and may prefer to leave the valve springs exposed so tapped 1/4 in. fine thread, to take an outlet pipe. that their working is visible, but the enclosure of In drilling the stud holes in both the cover- these parts does help to keep them clean and well plate and the cylinder-head block, it is of para- lubricated, besides reducing mechanical noise. mount importance to see that their location in the The cover may be made either from a casting or latter casting is correct in relation to the com- from sheet metal, and requires only to be faced bustion head cavities. It will be seen that on on the inner side. It is attached by means of two the sparking plug side of the casting, there is very studs fitted to tapped holes in the inner wall of little room to spare for the stud holes, and should the valve cavity, the holes being shown counter- one of them break out into the cavity, the casting sunk at an angle of 60 degrees, to fit knurled nuts is ruined. For this reason, it is advisable to mark having the ends bevelled at a similar angle. This out the positions of the holes very carefully ; do helps to provide a friction lock to deter slackening not rely on simply centring them from the boss of the nuts, but, if preferred, ordinary hand or positions in either of the castings. It may not spanner nuts, with spring washers, may be fitted. look quite so neat to see a stud hole out of centre with the boss, but it is even more important for Main Bearing Housing (Fig. 8) the engine to work ! However, the castings are A casting is normally provided for this com- sufficiently accurate for both requirements to be ponent, but it can quite easily be made from a fulfilled, so long as the marking-out is done piece of bar material, of a size large enough to clear carefully ; but one can imagine what might up to 1-1/2 in. diameter. The machining is quite happen with castings made carelessly, or from straightforward, and should be carried out at one inaccurate patterns. setting, so far as the essential locating surfaces are The best way to mark out the holes is to use a concerned. Note that the end face of the ball race scribing block, resting each casting in turn on a recess is relieved to prevent fouling of the inner ledge or strip clamped to the side of a heavy ring. The recess is bored to take a Skefko EE2 vertical block or angle-plate on the surface plate. single-row ball race, in the fitting of which a Mark out the longitudinal lines first, setting the plug gauge should be used, if available ; but, if scriber point to the required height, and marking not, the race itself may be mounted on the end of the top side of the cover plate, and both sides of a screwed mandrel and used as a gauge. Fit the the cylinder head at one setting. Shift the scriber race so that it will press in lightly, and make to the level of the next row of holes, and repeat certain that it goes right home in the recess ; an the procedure. The cross lines are produced in a undercut at the end of the recess is advisable if similar way, with the casting up-ended, and there is any doubt about this. The spigot of the located by a vertical strip on the angle-plate. In housing should be a snug push fit in the bore of the this way, the positions of the holes can be exactly’ main block ;note that the housing may be fitted verified, and nothing left to chance. When the at either end, according to the “hand ” of the main cylinder block is ready for drilling and engine and the direction of rotation. If there tapping, the head block may be lightly clamped should be any possible difference in the diameter in place and the holes “ spotted ” through in of the bores at the two ends, be sure and fit the position. Either 6-B.A. or 3/32-in. Whit. studs main housing at the right end. are suitable for securing the cylinder head. Water The nose of the housing is bored to take a communication holes are not shown on the detail steady bush, which may be used as an oil packing drawings, but will be dealt with at a later stage labyrinth seal in the event of a forced lubrication in the construction. system being fitted. This bore must, of course, be perfectly concentric with the ball race. Sump (Fig. 6) Machining of the outside of the housing is optional, Only the upper surface of this is machined, but a skim should be taken over the rim, and also and again, this is a simple chuck operation. The the outer flange face, to form a seating for the positions of the screw holes may be located from screws or nuts holding the housing in position. the bosses on the machined face, and after drilling These may be either 7-B.A. or 3/32-in. Whit. to clearance size for 7-B.A. or 3/32-in. screws, are Neat fitting of the housing spigots in the bore countersunk on the underside. Use these holes of the main block is essential, in order to avoid for spotting the positions of the tapping holes in taking the piston thrust stresses on the bolts the main block, when the latter are drilled and and screws holding the housings. tapped. (To be continued) 344 aroux arily PETROL ENGINE TOPICS open dowe regis * A 15-c . c. FOUR-CYLINDER E drillc betw By Edgar T. Westbury coun nece endI HE timing endplate, Fig. 9, can be machined ness with a micrometer at various points.Further togel T to suit either hand, according to which end machining on this part should be deferred for back of the engine it is fitted. Thus the boss on the present, until other parts are ready for fitting. size, one side is superfluous, and must eventually be the I machined away, but in the meantime, it serves a Timing Cover (Fig. 10) taPP useful purpose as a chucking piece for boring the In order to enable the timing cover to be fitted frorr ball-race housing, turning the spigot and facing at either end of the engine, two separate castings, I four the inner surface which seats against the right- or left-handed respectively, are available, take machined face of the main block. The fitting of but whichever of these is used, the machining equi operations are essentially bloc the same. The first opera- timi tion is the facing of the It inside joint face, which cam may be carried out by and holding it in the four-jaw way chuck. Then reverse the be I: casting and clamp it to witl- the faceplate, with the the main shaft boss set to run be c truly ; face and centre the mad boss and bore it to 7/16 in. the diameter. end A simple aligning plug dril is now made, one end of soft which is turned to 7/8in. lath diameter, to fit tightly in the the bore of the timing end- be plate, and the other to rear 7/16 in. diameter, to fit the insi bore of the cover, This I registers the two parts seal exactly in position for to I drilling the screw holes ign: will Fig. 9. Timing endplate den

Cr: the spigot and the ball- -I race is much the same as me’ for the main housing, strc but the bore is in this car case taken right through, ha\ so that the ball-race has as no positive end location i in either way. After com- w pleting these operations, sur the casting is reversed, stel and held by the spigot hes in the three-jaw chuck nat for facing the other side, and removing the un- :2 wanted boss. It is essential mi that the inner and outer faces should be parallel, 66 and this may be verified allc by measuring the thick- fin tar *Continued from page ba! 344, " M.E.,” March 20, oP Fig. 10. Timing cover us

412 THE MODEL ENGINEER APRIL 3. 1947 around the edge, to secure them together tempor- arily or to attach both to the main block for further operations. It may be considered desirable to dowell the parts together to ensure accuracy of register, in which case the dowel holes may be :/- / drilled from the back of the endplate, anywhere ‘\._ ,’ between the screwholes ; but with carefully fitted countersunk screws, this precaution should not be .-fB! necessary. The three upper screwholes in the endplate are tapped so that the parts can be held .her together without the screws projecting at the for back ; the rest of the holes are drilled clearance :ng. size, and after fitting the endplate in position on the main block, these holes are used to locate the tapping holes in the block, which follow through ted from the three lower holes in the timing case. A ‘gs, fourth hole is drilled in the timing endplate, to ale, take a countersunk screw, so that there are four ing equidistant screws securing the endplate to the ally block ; this hole does not come through the :ra- timing case. the It is now necessary to continue the bore of the ich camshaft housing through the timing endplate by and cover, in exact alignment. There are various iaw ways of doing this, and in a large lathe it may the be practicable to use a spigot mandrel in the chuck, to with the entire assembly mounted on it, so that the the centring and boring of both castings could be done in situ. Failing this, a piloted drill may be the made by turning a bar to a close running fit in in. the camshaft housing,with a hole drilled in the end to take either a centre drill or a short stub lug drill, which may be secured by a grub screw or of soft solder. This is used by running it in the in. lathe or drilling machine, to start the hole from in the inside of the endplate, after which it may id- be opened out with a larger drill, and finally to reamered. The procedure is repeated on the the inside face of the timing cover. his It should be noted that the machining of the seating in the timing cover may need to be varied 2: to suit alternative fittings or arrangement of the les ignitiondistributor, but, for the present, no harm will be done if it is machined as shown on the detail drawing.

Crankshaft (Fig. 11) The material specified for the crankshaft is medium alloy steel, about 35 to 50 tons tensile strength, but in view of present supply difficulties, constructors who are unable to obtain this may have to use mild steel, which will be satisfactory as to mechanical strength, but somewhat inferior in respect of wearing properties. It is hardly practicable to case-harden the crankpin journal surfaces because’ of liability to distortion. The steel should be normalised before machining, by heating to an even dull red and allowing to cool naturally ;this will release any internal stresses 2; produced in the rolling process, particularly in $2 cold rolling as applied in the manufacture of bright mild steel. The outside dimensions of the crankshaft are 6-1/2 in. by 1-1/8in. by 7/16 in., but it is desirable to allow a little on both the length and breadth for finishing ; the thickness is not quite so impor- tant, though it may be found convenient to use a bar 1/2 in. thick, and machine the sides after other operations are completed. Round bar may be used if desired, the oniy objection to it being the 413 THE THE MODEL ENGINEER APRIL 3, 1947 woulc amount of material to be removed, and the A good deal of the superfluous metal on the there; crankshaft may now be removed by drilling and difficulty of doing this by any other method than ing s eccentric turning, which may be a slow and sawing, but do not forget that the ends of the bar desig laborious process on a small lathe. The crank must be left intact to preserve the throw centres of an webs may be left circular if round bar is used, but until the machining of the crankpins is com- lems, there is no mechanical virtue in this shape, and it pleted. The oblique centre webs of the crank- and serves onlv to add weight to the crankshafttoo close shaft help to simplify crankpin turning, as they stiffei to the centre to have any substantial flywheel effect. give plenty of tool room and eliminate the need for beari] Marking out of the main and crankpin centres special long-reach narrow tools, such as are often squas is carried out in the usual way, by supporting or found necessary for work of this nature. As the bearil clamping the bar parallel to the surface of a flat shaft is of comparatively robust section, it should lengt plate, and using a scribing block to mark a centre be found possible to dispense with “ stretchers” mot01 line on both ends. If the bar should be distorted or other steadying devices, if due care is exercised crank so that it does not lie evenly on its supports, it and keen, narrow-pointed tools are used ; but j should be packed to eliminate all suspicion of should it be found desirable to do so. the gaps “ rock,”so as to ensure that the lines marked on may be stiffened by clamping straps across them, the two ends are in exactly the same plane. Next to bear firmly on the sides of the bar.The sloping turn the bar up on its edge, that is, at right-angles webs may be machined by turning from the to its first position ;it may be found desirable crankpin centres, producing-a convex surface, or 25’ to clamp it lightly to the side of an angle plate, square across from the side faces by milling, 32 DL with parallel packing blocks underneath. Set the shaping or filing, as desired ; the former method, scriber point to the centre height of the bar and in my opinion, produces the most shapely result, mark cross lines on each end, to indicate the and the most efficient disposition of material. 1 position of the main centres. The scriber may Finish the crankpins as accurately and smoothly now be re-set by measurement to mark the as possible, so that very little finishing by the use crankpin centres in a similar way, at a distance of of abrasive methods is required. 11/32 in. above and below the main centres Having completed the crankpins at both throw respectively. settings, the ends of the shaft may now be turned As there is some risk of error in measuring on the main centres. The most important point these distances, however, a positive check in this operation is to get the diameter of the ball on their accuracy, or at least their equality race seatings correct. It should not be necessary (which is the most important thing) may be to use undue force in fitting these races, but Fig carried out as follows : Centre-punch the inter- on the other hand, slackness must at all costs be section of the main centres at each end as avoided. The use of a very fine smooth file is the al accurately as possible. and make a small but permissible for fitting these races, and on the prove positive *indentation with a drill, either in a flywheel end, the journal may be very slightly practi machine or a hand brace. Next deepen the centre tapered, so that it is not necessary to press the efficie each end by means of a centre-drill running in race on all the way.Finishing of the taper may be multi] the lathe, the work being held by hand, with the deferred until the flywheel has been bored, as it is each 1 indentation at the opposite end resting against the easier to fit the mating tapers by working on the load, tail centre. The centre-drill should be of small outside surface than the inside. Screwcutting of as m size. with a pilot not more than 1/16 in. diameter. the threads at each end of the shaft should be the UI for producing a properly proportioned centre in done bv eeneratine methods if possible : the use suPPc of dies, except possibly for finishing purposes, is a shaft of this size. Now run the work between lJJe$ the main centres, and, by means of a point tool liable to result in “ drunken ” threads, which presented in turn to each end face, make a light tend to throw mounted components out of truth factor scratch to coincide as closely as possible with the and impose distorting strains on the crankshaft. marked radial position of the crankpin centres. Cyllr Remove the work, and check the distance between Why a Two-bearing Crankshaft ? Th these centres with dividers? aided, if necessary, Some queries and criticisms have been received been with a lens ;it is fairly obvious that it is possible on this point, many readers considering the two- to wit to work twice as accurately by measuring diameter bearing shaft“ cheap and nasty,” and expressing condi as compared to radius. Should the distance be preference for at least one additional bearing in consu found correct, the scratches may be deepened the centre , some would go even further, and weari with the point tool, so that risk of error in work- put a bearmg between each throw, making five have ing to the marks, with centre-punch and drill, are main bearings in all. There are, however, as “ reduced. But a slight error in the crankpin throw excellent reasons why I have adopted the simplest weari is of minor importance, providing that all crank- possible bearing arrangement, the first and most carbu pins have the same throw. Drill the crankpin important of all being the purely practical one of carbic centres in the same way as the main centres. avoiding difficulty in the lining-up of the bear- subse Should it be desired to modify the crankpin ings. The process of line-boring bearing seatings Th throw in order to alter the engine capacity, this in a crankcase as small as that on this engine is by can be done to a limited extent-it is possible to go no means an easy one, and although there are Carrie up to 3/4 in. stroke or down to 5/8 in. stroke-but it possible expedients to reduce difficulties in this exactl should be noted that this affects the length of the respect, it is questionable whether they are worth If the connecting-rod, which must be shortened if the the trouble involved. Any error in bearing ample stroke is increased, or vice versa, to the same alignment would, of course, result in binding, or inside extent as the difference in crankpin radius, in at least abnormal friction, so that the extra shoul order to bring the piston to the same position in bearings would be worse than useless. finish< the cylinder at T.D.C. Secondly, the fitting of intermediate bearings 414 THE MODEL ENGINEER APRIL 3, 1947 I 947 the would inevitably increase the length of the engine, turning the outside. The locating rim at the top and thereby adding to its bulk and weight, and reduc- of the liner does not need to be an exact fit in the :bar ing structural rigidity. Many motor car engine recess of the block, but care should be taken to see itres designers have found that an increase in the length that it will go in, and a slight allowance should be :om- of an engine exaggerates many structural prob- given on the length of the rim for finishing flush ank- lems, increasing the tendency to rocking couples with the top surface of the block after insertion. they and vibration,and unless the crankshaft is On no account should the liners be fitted too 1 for stiffened, it is liable to torsional vibration. Short tightly to their seatings in the block ; shrink fits &ten bearings are prone to rapid wear, as oil films are or heavy press fits are quite unnecessary, all that the squashed out at the ends, and in my opinion, is required being to ensure that the liner has a ould bearings in small engines should never be less in close contact with the seatings at top and bottom :rs ” length than their diameter. Many well-known and is not liable to turn or otherwise shift after ,ised motor cars have been fitted with two-bearing insertion. About 0.0005 in. is the correct amount but crankshafts, and instances have occurred where of interference if one has the means of internal and external measure- zaps lem, ment to a fine enough limit of accuracy. ?ing The main lapping the of the liners may be :., or - carried out before mg, the lap rod, insertion, nllt, being run in the rial. lathe, and the liner thly held in the hand use with a strip of rag row ned oint ball ;aly but Fig. 12. Cylinder liner (4 off) i be : is the addition of a centre bearing has not the proved advantageous in the light of 1tly practical experience. The way to the efficiency does not lie in the fitting of a r be multiplicity of bearings, but in arranging it is each bearing to carry its fair share of the q J-‘B-piq the load, and in vreventine shaft deflection Fig. 13. Valve liner (8 off) : of as much as possible. In this respect, be the use of ball races on the main journals, use supporting the shaft as close up as ? is possible to the crankpins, has been decided upon, wound round it to increase the grip. In this way ich after careful consideration, as the most satis- good control and “ feel ” of the lap is obtained, uth factory solution of the problem. and no distorting force is applied to the liner, such, t. as might happen if it were held in a chuck.If the Cylinder Liners (Fig. 12) liners are inserted before lapping, it is very The use of centrifugal or chill cast iron has difficult to get a sensitive “ feel ” on the block red ' been specified for these, as being the best material for proper control of lapping, and it is advisable YO- to withstand wear in the normal (un-heat-treated) only to carry out a light finishing lapping opera- ing condition, but steel may be preferred by some tion after they are inserted. in constructors, and if judiciously selected for its It should be possible to press in the liners by lnd wearing properties, will be quite satisfactory. I means of the lathe tailstock, using a drill pad in ive have found that a “ straight ” carbon steel such the socket of the barrel, and resting the casting ‘er, as “Pitho” wears well, and almost as good aaainst the facenlate. This will ensure a much est wearing properties may be produced by muffle- better alignment of thrust than is possible by ost carburising mild steel, so as to increase the using the vice or an improvised press for the of carbide content of its surface structure, without purpose.The outside of each liner should be given al.- subsequent hardening by quenching. a light coating of copal varnish, or even paint, rgs The machining of the liners is quite straight- before insertion, as this will serve the dual purpose by forward, and if the boring of the seatings has been of a lubricant during insertion, and a sealing carried out as directed, they may all be made to medium to prevent creepage of either water or K exactly the same external and internal dimensions. gas later on. rth If the length of the material available allows an It should be noted that the cylinder block may ing ample amount for chucking, they may be turned be bored to take liners up to 11/16 in. bore and 3/4 in. or inside and out at one setting, but failing this, they outside diameter, which, in conjunction with tra should first be bored to within about 0.001 in. of slightly increased crank throw, will enable the finished size, then mounted on a mandrel for (Continued on next page) rgs 415 A VACUUM PUMP N the photograph of the pump exterior. I is shown a vacuum This valve covers two pump to be used 1/16in. holes leading to 5 n the impregnation of the extreme bottom A coils. To the left of of the pump stroke. the pump is seen a The piston, 5/8 in. dia- of M vessel to contain the meter, has a groove place impregnating medium, packed with graphited Hestc and a stop valve to yarn. Making the Midc control the supply. stroke longer and in- ness. Both the pump and creasing the pump dia- cons1 container are mounted meter would reduce and on a fibre disc which the ratio of clearance on I has, interposed be- volume to the pump work tween it and an ordin- volume, so enabling a and ary jam-jar, a rubber better vacuum to be thea washer. The disc is obtained. Unfortu- St: retained firmly on the nately, increasing the Engi. jar by atmospheric diameter of the pump the n pressure when the increases immensely inten pump is used. the effort needed to led, s After making this lift the pump handle. to 1 apparatus, I filled a Perhaps the stroke of MOD small test tube with my pump could be in- tions mercury and inverted creased with advantage. desig it in a small glass con- Now I must make a tainer, also containing confession. I have mercury. This primi- never used this appara- gy tive barometer was tus for its original pur- placed in the jam-jar, pose. Bothersome In and I set to work with doubts have afflicted edito the pump. I found that me ever since making of a it was possible, with it. My chief doubt is : in pl much labour, to reduce will the atmospheric mode the pressure to 2 or pressure on top of the this. 3 millimetres. It is, of impregnating fluid be engir course, reducing the sufficient to force the this 1 pressure below about 2 fluid to every part of a Mr. centimetres which fine wire coil, or will Limi causes the greatest ex- voids be left ? I can for n penditure of work. think of no method of In Some hundreds of getting an accurate placi strokes of the pump. answer to this question. of m are needed to reduce the pressure in a r-lb. jam- I know that it is customary to apply pressure in mags jar to 3 mm. by means of my pump (5/8 in. diameter excess of atmospheric pressure to impregnating Locc X 3 in. stroke). The final vacuum depends on fluids in commercial practice ; so the problem cease the clearance volume needed for inlet valve and is a real one. the 1 the weight of valve, in this case a thin plastic 1/4-in. I am sorry to leave this question unanswered, At disc covering a 1/16in., hole. Tne outlet valve is a but perhaps some reader can supply the answer Gree band of thin plastic. material round the bottom to it.-P. GRANGER. Engi He, draw Farn Petrol Engine Topics upor (Continued from previous page) milit 1914 engine capacity to be enlarged to 20 c.c., should for finishing this. Do not drill the side port or the this be thought desirable. chamfer the valve seating until after the liner is aircr Either cast-iron or bronze may be used for the inserted, which may be done in the method Farn valve liners, the former being best for wear resis- recommended for the cylinder liners. He v tance, but the latter less liable to loosen through The block may now be mounted on the face- elimi differential expansion. They may be fitted rather plate and a fine finishing cut taken over the top macl tighter than the cylinder liners, as distortion of surface, including the rims of the liners, to pro- and the bore is less liable to occur and has less serious vide a dead flush joint face, which is finally lapped firing consequences. The bores of the port end and until its flatness, as tested on a true surface plate gum the guide must be kept perfectly concentric and is above suspicion. youn it will be seen that the end of the port bore is nicia spherical, a special cutter or D-bit being advisable (To be continued) bein! 416 THE PETROL ENGINE TOPICS The antethinf * A scrap 15-c. c. FOUR-CYLINDER ENGINE Th By Edgar T. Westbury be te! but s HE flywheel should be made from a mild taper bore the central boss, all at the same setting. owin T steel blank, if available, but as many A reamer may be used to finish the bore, if one is possi constructors may not be able to obtain available of approximately the specified taper, this, a casting in iron or gunmetal will be suitable. but should only be applied after boring to Personally, I favour gunmetal or bronze of within one or two thousandths of an inch of fairly good quality for flywheels, as its specific finished size. As already mentioned, it is advis- gravity is a little higher than iron or steel, and able to finish the flywheel bore first, and match therefore its momentum is greater for a flywheel the taper of the crankshaft to it. of given dimensions. Its appearance, however, The flywheel is secured to the crankshaft, may be objected to, though this may be improved or on a specially-made tapered mandrel (prefer- by dull plating, if desired. Whatever material ably the latter), which is run between centres is used for the flywheel, it should be machined all for finish-turning the exterior surface. With over, with due care to keep all parts concentric due care, this method should produce a flywheel with each other (Fig. 14). which is perfectly true all over. It is surprising Recommended procedure for machining the how many wobbly flywheels one encounters, flywheel is as follows : First chuck the blank but there is no excuse whatever for this state of or casting with the pulley end outwards, and affairs-even the old, old story that the lathe rough turn as much of the outside as is accessible “ won’t turn true ” isn’t good enough in this at this setting, including the groove, leaving not case ! more than about 1/32 in. for finishing. If a casting is used, it will be possible to grip it by Balance the inside of the rim, so that the whole of the When steel or other bar stock material is 1. may but ensu: at tb any balar centt shou sions Ba engit twin, like swee well- ““g: balat althc be b weig cylin dyna pisto Fig. 14. Flywheel as in twin are s. tend outer surface can be turned ; but if working used, the flywheel should be perfectly balanced the ( from a blank, only a part of this surface is when machined all over concentrically, but this and accessible. Next, reverse the work, holding it does not necessarily apply in the case of a casting, the I as truly as possible, to turn the rest of the surface, as the material may not be perfectly homogeneous, In including the recess and the back face of the rim, and may even have concealed blow holes below rock which may be finished to size right away, also the surface. It is good policy, in this event, to one rough turn any part of the rim not accessible at test the static balance of the flywheel by rolling othei the previous setting ; then centre, drill and its mandrel on knife-edges, and if an error is beta found, correct it by drilling the inner side of the as s *Continued from page 416, ” M.E.,” April 3, rim on the heavy side, or by running a little coup 1947. soft solder inside the rim on the light side. cran: 488 THE MODEL ENGINEER APRIL 17, 1947 The latter is perhaps the best way, as quite a and assuming reasonable structural rigidity in thin film of solder, not sufficient to affect appear- the engine, produce no external effects. This ance much, is usually adequate, and it may be applies not only to four, but also six, eight or scraped away to obtain fine adjustment of balance. more cylinders when arranged side by side in The static balance of the crankshaft itself may the same plane. If, however, the weights of the be tested out and similarly corrected if necessary, opposed reciprocating or rotating pairs at the two but static balance, in this case, is not sufficient. ends of the engine are not equal, they do not ting. Owing to the length of the crankshaft, it is cancel exactly, and vibration or rough running ne is possible that serious errors in dynamic balance will result. iper, : to Pistons h of These are illustrated in Fig. 15, and it will be ivis- seen that they are intended to be made from atch castings in iron or aluminium, and to be fitted with rings. At the moment however, it is not 1aft, certain whether piston rings of the size required :fer- can be obtained, and although it is possible for itres the amateur to produce rings which will work With satisfactorily, this is an extremely delicate job heel which most constructors will probably wish to sing avoid if possible. Plain pistons machined from ters, cast iron, and fitted to the finest possible clearance .e of in the cylinders, will give quite good results, athe and unlike two-stroke engine pistons, the presence this of the empty ring grooves will do no harm ; in fact, they are advantageous, as they will help to preserve an oil seal. The procedure for machining pistons from the solid has been 1 is described several times, in connection with the Fig. 15. Pistons (4 off) construction of two-stroke engines, and need not be repeated here. It is desirable to make the may exist although static balance is perfect, pistons as light as possible, and each should be but this may be avoided to a great extent by exactly the same weight. ensuring that the distribution of mass is equal If there is any variation in the diameter of the at the two ends of the shaft. In other words, cylinder liner bores,selective fitting of the any parts which might conceivably be out of balance, such as the end webs, the diagonal centre webs,and the crankpins themselves, should match, end for end, in respect of dimen- sional uniformity. Balance is, perhaps, more important on an engine of this type than on the usual single or twin, because it is really capable of something like perfect balance if due care is taken, and the sweet running and absence of vibration of a well-balanced four-cylinder is one of its most impressive characteristics. For the benefit of those who have not studied balancing problems, it may be mentioned that although the reciprocating weight of a piston may be balanced by that of another piston of equal weight moving in opposite phase-as in a twin cylinder engine with opposed cranks-true dynamic balance can only be obtained when the pistons move in exactly in the same plane- as in the opposed piston engine, or an opposed twin with no “ offset.” But when the pistons are side by side, their motion produces a “ couple,” tending to rock the shaft about a point between ted the crank throws ; and the effect of this can be, this and often is, much worse than that produced by Fig. 16. Connecting-rods (4 off) ink5 the unbalanced reciprocating weight. MS, In the normal type of four-cylinder engine, the pistons is necessary, and each one should be low rocking couple is cancelled out by opposing marked to show in which cylinder it belongs. , to one half of the mechanical system against the By the way, it is usual to number the cylinders ling other half ; this is known as “ mirror ” balance, from the timing end, but either way wiil do, r is because one half is the counterpart of the other so long as it is decided upon definitely, and as seen by reflection in a mirror. Rocking adhered to. Aluminium pistons will not be 2: couples are then produced in each half of the entirely satisfactory unless fitted with rings, ide. crankshaft, but they are equal and opposite, as they call for greater clearance to allow for 489 THE MODEL ENGINEER APRIL 17, 1947 THE t' expansion, and will therefore fail to produce a the big-end, the parallelism of the two eyes is good compression seal when starting up from cold. definitely assured. When set for the first rod, the end fat The advantages of reduced weight and improved rod is fixed in position for the other three, and h: heat conductivity of aluminium pistons are not which will then ensure that the length of the rods three likely to make much difference to performance between eye centres is exactly the same. outside in so small an engine. If machined in this way, there should be no oil crew question about the correct alignment of the rods It h Connecting Rods (Fig. 16) when assembled, but in order to check up on any tappet possible errors, the rods should all be assembled awkwa Cast bronze rods are the simplest form of bush s construction, and give quite satisfactory results on the crankpms, and the crankshaft temporarily assembled in its bearing endplates. The position throug in small engines for speeds up to 7 or 8 thousand guides r.p.m. Duralumin or steel rods, machined from at thiz the solid, may be preferred by the more fastidious may t worker, but show little, if any, advantages in go to practice, and in the latter case, bronze or anti- friction metal linings would have to be fitted Valve in both big and little ends, which would conse- Altl- quently have to be enlarged in diameter, increasing valve bulk and weight. than 0 The four rods should be identical in the length have between the eye centres, and also uniform in stee!, weight when finished. If castings with solid Fig. 18. Valve tappets (8 off) cuttml big-end eyes are used, there should be sufficient specia metal to allow for splitting and cleaning up the machi faces of the bearing, after rough drilling the eye of the rods can then be seen from the tops of the ponen and also the bolt holes, and marking on the sides cylinders, and it will be instantly apparent if The of the bottom lugs, to number the rods and show they are out of centre ; this should be checked parted positions for assembly. For splitting the eyes, at both ends of the stroke, and correction made, if necessary, not by bending the rods, but by EilPf$ machining away the face of the little end boss. It is better to allow plenty of side play between the availal little end boss and the piston bosses than to risk down binding on either side ; but the dimensions shown on the drawings do not allow for definite end play, because of the desirability of obtaining maximum permissible bearing length in the little ends. T E Gudgeon Pins (Fig. 17) in the Fig. 17. Gudgeon pins (4 off) These may be made of mild steel and case- hardened, or of high-tensile steel, without Imita a circular saw running in the lathe is advised, subsequent hardening. They are drilled through the rods being held in the tool post, with packing the centre, and fitted with soft brass or aluminium J?liTi above and below, and with the centre line end pads in the usual way. exactly parallel with the lathe axis. This will :lE;k” leave truly finished surfaces, which require Valve Tappets (Fig. 18) has ac hardly any further treatment, beyond a slight These also are best made of mild steel and soft r, rub on a smqoth file to remove burrs. The lower small half of the bearing has the holes opened out to 45'CHAM.. clean clearance size for the fixing. screws, the upper 3* 8 B.A. / ,52DIA. / i few : half being tapped, after which temporary screws form are fitted. and the rest of the work on the rods furthc is the same as that for the more usual solid-eye type of rod. Dead It is a good policy to bore the little end of Im each rod first, holding the rod in the four-jaw nitrat chuck, with the boss central, and the centre silver line of the rod parallel with the chuck face. to ilr The end of the boss can be faced at this setting, Blat! and it may also be found advisable to skim up the ’ Im tapered outer surface as far as it can be reached. Fig. 19. Valves, with adjusting and locking Similar treatment may be applied to the other nuts (8 off) Blat: end of each boss, by mounting the rod on a stub Im mandrel. Next make a locating pin to fit the case-hardened. They consist of light thimbles, bore of the eye, and mount this squarely on a eight in number, which should be finished to a Blue steel block which can be clamped in the groove smooth sliding fit in their guides. In order to Im of the four-jaw chuck, in place of one of the jaws. lighten them as much as possible, they are drilled An a By setting the eye of the rod on this pin, at in the centre, and the end of the hole should be the : the required distance from the chuck centre, finished with a flat-ended drill or D-bit, cham- Sligl and using the other three jaws to centralise fered or rounded at the corners. The bottom CO 490 947 THE MODEL ENGINEER APRIL 17, 1947 s is the end face should be finished dead smooth and true, size, chamfer off the end, and support it with a and hardening is essential. If desired, two or hollow centre while turning the rest of the shank. ree, A slight radius should be left under the head, ,ods three fine oil grooves may be turned in the outside of the tappet to distribute oil and check and the seating face should be turned by setting oil creeping. over the top slide to 45 degrees-not by the use II0 of a bevel forming tool, which is very liable to ,ods It has not been thought necessary to bush the tappet guides, as this would call for a somewhat leave waves in the finished surface, and thereby any prevent the valve from seating properly. Iled awkward boring operation, the diameter of the bush seating being larger than the entry passage It is important that the shank of the valve lrily should fit the guide closely, so as to avoid the tion through the valve port. The side thrust on the guides is not heavy, and no great wear and tear possibility of air leakage, but it must on no account at this point is expected ; but bronze bushes be tight or sticky to cause sluggish or erratic may be fitted if the constructor is prepared to action of the valve under working conditions. go to the extra trouble entailed in doing so. Owing to the small diameter of the valve stem, the problem of retaining the spring is a Valves (Fig. 19) rather delicate one, as the usual methods were Although it is not necessary to use special impracticable, and it has been decided to use valve steel for making these, something better screwed valve stems, with lock nuts, as this than ordinary mild steel is desirable. Good results method has proved highly satisfactory on the have been obtained with 3 per cent. nickel “ Kinglet ”and other small engines. This also steel, and also with stainless steel of the “ free provides an extremely simple method of tappet cutting ” grade ; high-tensile stainless and other adjustment. The upper nut is shouldered to special steels are generally very difficult to centre the spring, and the lower one is a standard the machine, and are best avoided for delicate com- thin lock nut ; both nuts should be case- tt if ponents which call for accuracy and good finish. hardened, and it will be noted that the thrust :ked The valves may be turned at one setting and of the tappet is taken on the face of the nut, not ade, parted off, the use of a running-down tool being on the end of the valve stem. A slot should be : by helpful for ensuring a smooth, parallel finish cut across the valve head, so that a screwdriver )OSS. on the shank. If only the ordinary tools are can be used to hold the valve while adjusting L the available, however, it is advisable first to turn and locking up the nuts. risk down the extreme end of the shank to finished (To be continued) :ions mite Chemical Colouring of Metals ning Bv G. Woodin little HEfollowing are useful formulae for surface when immersed in a solution of ammon- T the chemical colouring of various ium sulphite I oz. and water 4 oz. When brass metals, and have proved most useful is immersed in this liquid it will take on a steely- grey colouring. :ase- in the making of model ships fittings, etc. hout Imitation Silvering of Brass, Copper, To Tint Aluminium Blue mgh Iron or Steel Dip metal in a hot, medium strong solution dum Place a globule of mercury, about the size of a of caustic soda (sodium hydroxide) for a few pea in a mortar, add two teaspoonfuls of powdered seconds then rinse in warm water and dip in a chalk and grind for half-an-hour until the chalk hot solution of an aniline dye. The metal will has acquired a grey colour. Moisten the end of a then be permanently tinted. and soft rag with methylated spirit, then take on it a small quantity of the powder. Rub this over Dulled Aluminium clean surface of article to be silvered. In a Dip metal in hot, medium strong solution of few seconds a thin shimmery silver film will caustic soda. form on the surface which can be thickened by a further application of powder. Golden Colouring of Brass Dead Black Colouring of Brass or Copper Immerse in a very dilute solution of ammonium Immerse article in a liquid of I oz. of copper or sodium sulphide. nitrate and 3 oz. of water. A small quantity of \ silver nitrate dissolved in this solution is said Red Colouring of Copper / I”’ to improve colouring, but is not essential. Immerse as above.As strength of the solution gq varies so can almost any red, yellow, brown or Black Colouring of Silver black colour be obtained on the metal. Immerse in a solution of sodium sulphide. w Black Colouring of Zinc Tinting Brass Immerse in solution of antimony chloride. Brass can be given tints varying from pale bles, gold to pink and pale blue by immersing in a to a Blue-Black Colouring of Iron solution of 1/2 oz. each of lead acetate and hypo to :r to Immerse in a solution of photographic hypo. I pint of water. illed An addition of a little lead acetate or nitrate to d be the solution improves the colouring. Greying Iron Iron can be given a grey colour by boiling lalll- Slightly Shiny Black Surface for Copper Etom for half-an-hour in a weak solution of iron Copper will acquire a slightly shiny black phosphate. 491 PETROL ENGINE TOPICS *A 15-c.c. FOUR-CYLINDER ENGINE By Edgar T. Westbury E come now to a part of the construction engine can testify.The present engine has twice which involves quite a few knotty prob- as many cams, and they are smaller in dimen- lemsW in layout and execution ; namely, the sions, but the same methods are applicable, and I camshaft and timing gear. Many prospective propose to adapt them, with suitable modification constructors of multi-cylinder engines have been of detail, to the job now in hand. deterred by the apparently formidable task of It may be remarked that in the making of a making and setting the cams ; while others, camshaft, one has the choice of making the cams starting out lightheartedly, but with no very separately, and mounting them on the shaft, or definite idea of procedure, have met their machining the cams in position as an integral part Waterloo when this stage of construction was of the shaft ; just as, in steam-engine construc- tion, cranks and eccentrics may be built up or In a published design for a multi-cylinder machined in one piece. To many constructors, engine, which I once examined, the camshaft it may appear that the former method is the details supplied were very vague, and the instruc- simpler, and this is quite correct in certain cases. tions “ File cams as required ” struck me as It would, for instance, very much simplify the being delightfully optimistic ! While it is no production of the cams, and ensure their complete doubt possible to make a camshaft in this way, uniformity of shape, if all of one kind were the chances of it being accurate, either in respect clamped together in a bank, and formed at once. of cam contours or their timing, are very remote ; The four inlet cams and the four exhaust cams and it is equally unlikely that an engine fitted with could thus be dealt with in two operations. such a camshaft would develop the best possible Unfortunately, however, with cams made in this efficiency.Much of the success of multi-cylinder way, further problems arise, not only in the engines depends upon obtaining equal efficiency secure attachment of the cams to the shaft, but from all the cylinders, and the importance of even more so in ensuring their correct relative uniformity of valve lift and timing is beyond all position to other cams. I do not know of any question. really simple way of setting separate cams of the However, like many problems in life, the size now under consideration, in such a way as to oat. tch. .ally and her rail. the sea low iter lres igh we ng

Fig. 20. Contours of inlet and exhaust cams (four times full size) of 4, anticipation may be worse than the real thing, and be quite sure of their correct angular location of it is possible, by adopting commonsense methods, within a limit of one degree of camshaft angle, ar. to make the production of an accurate camshaft which represents two degrees of crankshaft ml not only a fairly straightforward, but also an angle. II-IS interesting exercise in machining. In the con- For this reason, I strongly recommend the use zre struction of the twin engine for “ I83I," problems of a solid camshaft with all the cams formed on it. Ifl- of a similar nature were encountered, but the This calls for careful setting out, and it is obviously methods evolved for dealing with them proved to necessary to eliminate the possiblity of errors, as he be highly effective, as many constructors of the they cannot afterwards be corrected ; but it ‘1Y enables the cams to be timed to a very close limit re *Continued from page 491, “ M.E.,” April 17, of accuracy, and there is no risk of individual cam ed 1947. timing ever becoming altered. ‘s- 553 THE MODEL ENGINEER MAY I, 1947 Camshaft Blank the utmost ounce of efficiency from the engine, Details of this will be given later, and its pro- though the latter consideration has not been duction is a fairly simple turning operation, which entirely neglected. In other words, the shape is can be carried out between centres. The material a compromise between that which gives best recommended is a good case-hardening mild or results, and that which is easiest to form accur- low alloy steel, and if one is able to exercise any ately ;and this is true of most cams used in choice in the matter, try to select a make or grade automobile practice, other than those of specially- that can be guaranteed to distort very little in made racing engines. quenching.Steels vary enormously in this respect, The duty of the cams, at speeds within the but if little is known about the steel used, range for which this engine is designed to work, normalising before machining is helpful. is fairly easy, as the inertia of the moving parts of Hardening of a long shaft is always bound to the valve-gear is kept as low as possible ; in this be fraught with some risk, and it would be very respect, it may be noted that a side-valve engine nice if we could dispense with it in the case of a is at a great advantage over one with overhead component which calls for a good deal of previous valves, especially when the latter is designed for machining, such as a camshaft! because it is a high performance, involving maximum strength serious matter if the part is spoiled by distortion and rigidity of valves, rockers and push-rods. or hardening cracks. However, a soft cam is Direct operation of the valves through the light impracticable, as it would soon lose the accuracy thimble tappets relieves the cams of a great deal of its profile, even if made of fairly hard-wearing of inertia load, and conduces to smooth, effortless material. The only possible‘ alternative to working. hardening is the deposition of a hard chrome Fig. 20 shows the contours of the inlet and layer on the steel, which I have not tried out for exhaust cams respectively. It will be seen that this particular purpose. both are symmetrical and have convex flanks, the t It is practicable to straighten a distorted shaft, flank radius being the same in each case, but as though this may be a rather tedious job. To the opening period, or angle from the base of one Q facilitate it, and avoid cracking, the shaft between flank to that of the other, is greater in the case of the cams should be left soft, but there may be the exhaust valve, the nose of the latter is corre- some difficulty about this in practice. In produc- spondingly broader. For convenience in forming, 2 tion, the usual method of obtaining soft zones in all curves in the cam contours are built up of true. inl a hardened component is to leave these parts well circular arcs ; and as the flank curves are all the ful oversize until after carburising, and then machine same, the difference in opening period is allowed 29: away the carburised surface, prior to reheating for by making the radius at the nose different in Ch and quenching. There are other ways of pro- the two cases. ducing local hard and soft zones in machined The relative positions of the inlet and exhaust Ar parts, but generally speaking, they are either cams are determined by reference to the timing more troublesome or less reliable-sometimes diagram, which is shown in Fig. 21. In accordance CYl both. with normal practice, this is set out in terms of rel All this may sound very complicated, but it will crankshaft angle, and the opening and closing Cyl be found much better to consider all eventualities position of each valve is measured from the top I-: than to blunder in with haphazard methods and and bottom dead-centres respectively. The the finish up, as likely as not, with a spoiled camshaft, timing is fairly normal for an engine of this type, idl after many hours of patient work. with the exception of the fact that as r.p.m. will be ti0 To avoid the risk of hardening cracks develop- higher than most full-sized engines, and lost Tl ing, small but definite internal radii should be motion in valve gear relatively.great, the opening left in all corners of the camshaft. This may periods and “ overlap ” are slightly on the full Es appear to be a very small matter, but a “ fillet ” or side. This policy, it may be mentioned, has been wi radius helps to distribute stress and to prevent the suggested by experience in timing these small formation of a focal point from which a crack may engines. sei start and spread. I know of many failures in Having decided on the valve timing, it is now rn: highly-stressed parts, not only in models, but also necessary to translate the timing diagram in terms ea in full-sized engines, which have been directly of camshaft angle, which, of course, involves due to stress localisation in sharp corners. halving all the angles ; it is also more convenient El Hardened parts are particularly important in this to work around the circle from o to 360 deg. respect, as the sudden change of state in quenching instead of working from top and bottom centres EZ introduces surface stresses in the metal at the of the crankpin or piston. A single stroke of the dc corners. piston only represents 90 deg. of the camshaft en It is advisable, though not absolutely necessary, diagram, and there will thus be two top dead is to defer the finishing of the journals at the ends of centres and two bottom dead centres shown, but tn the shaft until after the cams are formed, but they the diagram starts from the top centre of the or should be turned to a definite size to facilitate firing stroke, which is the zero point in the nc their fitting to the cam forming jig, which will be diagram on the right of Fig. 21. av described later. To further clarify this diagram, the cam contours are superimposed on it, so that the Cam Contours juxtaposition of the inlet and exhaust cams for Before machining the set of cams, their con- any one cylinder of the engine, and their relation tours should be fully determined and understood. to their respective crank centre, may be clearly i It may be remarked that the contours selected for seen. It will thus be observed that as the cams these particular cams are dictated more by con- rotate, the exhaust cam commences its lift at venience in production than the desire to obtain 60 deg. from zero point, reaches its full lift at 554 teJ THE MODEL ENGINEER MAY I, 1947 en is :st .r- in Y- le k, of lis 3e id or th Is. ht al ss

td at ie 3s le Fig. 21. Timing diagrams, in terms of crankshaft and camshaft angles respectively 3f :- 125 deg.,and completes its drop at 195 deg. manifolding of inlet and exhaust pipes. & Before the period of this cam is completed, the The sequence of the cams can be seen clearly le inlet cam has begun its lift at 175 deg. ; it reaches by reference to Fig. 22, in which the letters te full lift at 235 deg.,and completes its drop at A B C D E F G H refer to the cams in order of ,d 295 deg., leaving 65 deg. to complete the full their endwise positions on the shaft, and the n circle of rotation. angular position of each cam is shown, in its relation to the top dead centre of No. I cylinder. Arrangement of Eight Cams Note that as No. I and 4 cylinders have their This gives the positions of the cams for one cranks in the same plane, but fire on alternate cylinder only ; it is now necessary to consider the revolutions, their pairs of cams are in opposite relative positions of the cams for the other three phase. Nos. 2 and 3 cylinders similarly have cylinders. The firing order for this engine is their pairs of cams in opposite phase to each 1-2-4-3, starting from the timing end, and as other, but displaced either 90 or 270 deg. to the the camshaft is geared to the crankshaft with an corresponding cams of Nos. I and 4 cylinders. idler in between, it will rotate in the same direc- As I have, on many occasions, reminded tion, which is anti-clockwise at the timing end. readers that it is one thing to design components Thus the sets of cams for the four cylinders will on paper, and quite another to make them exactly come into operation in the order given, each set as designed, I shall proceed in the next instalment being 90 deg. behind the other in an anti-clock- of these articles to show how the cams may be wise direction of rotation. produced with simple equipment. There are several pitfalls for the unwary in the setting-out of a set of cams, as I can testify, having Dead-but Won’t Lie Down! N made quite a few mistakes in my time ! It is very Several times in the past I have had to refer, LS easy to set the cams to give the wrong direction of almost in apologetic terms, to the ancient design :S rotation, or to put the inlets where the exhausts of engine known as the “ Kestrel,” which was 1t have to be. Correction of these mistakes is introduced to readers in 1937, and might there- :. practically impossible, so it is advisable to think fore be expected to have earned retirement on a :S hard before acting. Note that the sets of cams pension. But somehow, the engine-or its con- e do not follow in ordered sequence, as regards the structors-will not accept dismissal, and though 3 endwise position of inlet and exhaust cams ; there “ old and rough, and dirty and tough,” like d is first an exhaust cam, then two inlets, Barnacle Bill, it refuses to settle down to a decent It two exhausts, two more inlets and finally and discreet senility. I mentioned some time ago e , one more exhaust. These positions have that die-castings for this engine had been pro- e not been selected just to make it more duced by Mr. L. D. Johnson, of Birmingham, and awkward for the constructor, but to simplify it is now brought to my notice that Mr. S. A. n e A B D E F G H mr n Y S .t .t IN3 fN4 EX4 Fig. 22. Relative angular positions of cams, with No. 1 piston at top dead centre

555 THE MODEL ENGINEER MAY I, 1947 Smith, of Chatham, is using these castings in the “ Future Plans ” production of finished engines? one of which has Many thanks to the numerous readers who been submitted to my inspection. have responded to my invitation to record their I find that the workmanship is very good views on this matter. The letters received are all indeed, and carried out faithfully to the original extremely interesting, though hardly any two of design, with the exception of one or two minor them express quite the same opinions, and it details, such as the use of a plain iron piston would appear that the “ Ideal Petrol Engine ” is VC instead of an aluminium piston with two rings-a as elusive as the “ Ideal Lathe ! ” However, there when modification which is quite in order and in is no doubt that they will be of great value in vided keeping with shaping policy in omitt modern practice. future articles and Fit- -c The sample designs. cylinc submitted started With regard main, up readily and to the judging ran quite con- of these entries, sistently, though a somewhat dim- being new, and cult problem a little on the arises, in that stiff side, no at- a few of the tempt was made letters are from to force the pace my personal or to obtain very friends, and as high performance. I am most Mr. Smith sup- anxious to avoid plies this engine any possible sus- fitted either for picion of favourit- aircraft or racing- ism, I have de- car installation, cided to submit and is prepared the entries to the to undertake tun- judgment of in- ing for high effi- dependent per- ciency. The sons. The result that appearance of the of the competition engine is good, will be announced 2% largely due to as soon as possible oil tl the quality and and it is likely of thl accuracy of the that in view of valve die - castings, and their general in- rema those who are erest, it will be detai looking for a found desirable to geon sound, reliable publish several As and well-designed of the letters, in and engine, might do part or entirely, valve much worse than in THE MODEL must try this genuine A 5 c.c. Kestrel engine, as produced by Mr. S. A. Smith ENGINEER. one antique design. from die castings supplied by Mr. L. D. Johnson (To be continued) passa large forcil a rou An Exhibition of Models in Sussex see I in pa bush The first annual exhibition of the Mid-Sussex engine. A silver cup, given by the club for the best model by any visitor, was awarded to Mr. prevc Model Engineering Club was held recently, bush at the Public Hall, Haywards Heath. There E. L. Mead, of Brighton, and the second prize were models of every description on view, includ- of £I voucher went to Mr. D. Lockett, of Burgess as th’ ing a model passenger-carrying railway, the track Hill. Will of which was recently constructed by some of the A 3-1/2-in. gauge “Maisie” locomotive, kindly roun club members, and a film show. loaned by Mr. D. L. Venus, of Hassocks, did right most of the work on the track, and Mr. Sulivan, for tl Prizes for the best models exhibited were press given as follows : of the Sutton Model Engineer Club, also loaned his 3-1/2-in. gauge “Silver Queen” locomotive keep A silver challenge cup, to be held for one year, wher presented by Mr. K. Banks, for the best model on the last day. B made by a member of the club, was won by Another attraction was a cinema show with Mr. W. Warnett for a 2-1/2in. gauge “Fayette” films kindly loaned by the Southern Railway. t.hOl type locomotive ; Mr. F. Wilkins was awarded The exhibition was a great success, and the the second cup, given by Mr. Whittington, for a club takes this opportunity of thanking all who *c 2-1/2-in. gauge “ Dyak” locomotive, and a third made it possible. 1947, prize of £1 voucher given by the club went to Hon. Secretary : A. L. PALING, 31, Broadway Mr. A. Funnell, for an 15-cylinder radial petrol Buildings, Haywards Heath, Sussex.