HRP Motion Components

In order to keep this chapter to a reasonable length, the three types of motion components are being dealt with together, the general subject matter of the text applying to all engines. The paragraphs which specifically apply to one type of engine or component only, have their heading brought out in bold type, so that the reader can easily recognise that which applies to his own particular model.

CRANKSHAFTS

There are various ways of making crankshafts, but if one is building a model as elaborate as a traction engine or roller, it seems very worthwhile to fit the engine with a crankshaft made in the best possible manner. One sees many crankshafts which are fabricated, and whereas these can be perfectly true, the various components must be made to very high engineering standards to ensure that this truth is a permanent thing. The crankshaft is undoubtedly one of the most precise components in a model, let us therefore make it from solid. The finest way to produce a crankshaft from solid is to use a flame-cut blank, whether it be for a single-throw shaft as for the BURRELL, or a double-throw shaft as for the FOWLER. The only basic difference is that the single crankshaft will be flame-cut at one pass* whereas two-throw crankshafts will heed to be cut in two stages, at right angles to each other, Follow^-ing flame-cutting of the blanks, they are best normalised white hi the rough state. This process is basically to bring the blank up to red heat, and to hold it at this heat, or let it soak in it, for a number of hours, when all stresses in the metal will be relieved; thus there will be no tension in the blank, and during machining, the shaft is unlikely to go out of true. The reader wiH realise that a shaft has balanced stresses present, which have been produced firstly, in rolling the plate itself, and secondly when the shaft was flame-cut; these stresses would be balanced with the flame-cut in the raw condition/However, as the machining of this blank progresses, there must come a stage when this balance (i.e.: equal and opposite forces) is upset, and the crankshaft blank must move, in order to bring about a condition of equal balance once more. Taking the normalised blank, drill the centres on which the crankshaft will be turned. (Two at each end for the BURRELL and three each end for the FOWLER.) The usual practice with these blanks is to leave a web or flange on the end of the shaft, so that centres can be drilled to hold the work while the machining is carried out; afterwards this portion of the blank will be cut off (See drawing 17).

Commence by cleaning up the end of the blank with a file; it is essential that any burrs or residue from the cut should be removed, so that the blank can lie truly on a flat surface, e.g.: machine table or drill base. Now take a piece of strip steel approximately the width and length of the end of the blank, and scribe a centre line down the middle of it. Carefully centre-pop the necessary locations for the crankshaft centres, i.e.: exact length of throw. After carrying this out, drill holes through these centres, and another hole for bolting the jig plate in position. Next drill and tap the ends of the blank, and with the blank and drilling jig plate resting down firmly on a flat surface, tighten the bolt so as to lock the plate in place. Now drill the pilot holes deeply enough, so as to give a good location for a centre drill to follow. At this stage, the jig plate should be removed and taken straight along to the other end of the shaft without being turned, and the same procedure carried out again, being sure that the jig plate and crankshaft are still on the same side and resting down, before bolting up tight. With the FOWLER Showman's engine crankshaft, there are three centres necessary on which to carry out the machining, but the same basic procedure is carried out, thus ensuring that the centre holes will always be in line with each other and that no twist will occur. The centre distances will be identical, and they must be in the right position relative to each other. The next stage is to put a centre drill in the lathe chuck, then, with the work beween this centre drill and the tailstock centre, produce correct centre locations in place of pilot holes. It is a good idea at this stage to drill and tap a hole in the side of the end web of the crankshaft blank (i.e.: in the flange which houses the centres). A piece of strip metal may then be bolted solidly on to the side of the blank, to act as a very effective driver during the machining operations. This driving strip can be lightly clamped against one of the chuck jaws of the lathe. For the greatest accuracy, it is best to put a piece of steel rod in the chuck and machine a centre on which to carry out the machining of the crankshaft. The fact must not be overlooked that when the final machining has been carried out, it is likely that you will put the crankshaft out for final grinding, and therefore it is essential that the centres are true if the work is to clean up properly. If a light clamp is used as previously mentioned, it is a wise procedure to tie this to the chuck with string, purely as a safety measure. String is best, since it has a certain amount of stretch in it and is unlikely to come loose. It will be best to machine the major portion of the centre webs while the main shafts are relatively untouched; in this way the crankshaft has the best possible support during the heaviest cutting operations. Do not machine the crankshaft right down to size straightaway, as there is always the possibility of some small amount of movement taking place, even after normalising, so one should aim at getting the blank generally down to size in the lathe. The webs can be brought to correct width, and then, before any final turning is carried out, the blank should be put up on the milling machine or the lathe, and the webs machined to finished thickness. If the webs are to be milled or filed round, this should be carried out before the final turning, since if any stress remains in the shaft, machining will most upset the balance in the area of the webs. It is a good idea to put the shaft aside now and leave it for a week, ia which time any likely movement will have taken place, after which time finish turn your shaft to size, producing as high a turned finish as possible and leaving the journals approxi- ", mately .0005" oversize. Then a final high polish can be obtained with emery cloth. If you decide to have the shaft ground, then leave all the journal diameters .010" to .012" oversize, but certainly no more than .015"; machine any flanges at the edges of the journals, to dead width. The grinder will then finish the journal diameters on size and just brush the side flanges, thus saving the expense of extra measuring. After grinding, the end flanges of the blank should be | cut off, but make sure to leave the mainshaft centres in position, as these will be required when splining or slotting is carried out.

The BURRELL crankshaft has slots machined into the shaft, leaving the keys of the male spline solid with the shaft itself. The slots can be shaped very accurately in the lathe, or may be spline ground. If the slots are to be shaped, a fairly large lathe or actual shaper working in conjunction with some form of dividing attachment will be needed. With the lathe, it should be possible to utilise a headstock gear and peg; you will need a gear with a number of teeth divisible by six (Burrell). The best way to proceed is to have your crankshaft gears professionally broached (where the model you are building employs a British Standard Spline). Having had the gears broached, take one of these and damp the inside of the spline with paraffin; then stand this gear down on a piece of plasticine large enough to cover and seal the bottom end of the spline. Now take some 'Flowers of Sulphur' (a yellow powder, obtainable from most chemists), put some of it in a tin, and gently warm it, the idea being to melt the sulphur without burning it. Care must be exercised to prevent burning; therefore it is best, if using a gas ring, to put a steel plate over it, or a plate on an electric cooker can be used. Proceed as follows:-Gradually warm up the sulphur, making sure it does not smoke (if it does smoke it is too hot) and it should gradually become liquid. When it is completely liquid, it will be ready for pouring; at this stage the sulphur should be extremely fluid (like water). However, if the sulphur is overheated, even slightly, it will thicken (like treacle); this is a peculiarity of sulphur, but it only needs to cool a little, and it will once again become fluid. Now pour the sulphur into the bore of the gear until this is full to the top; leave it long enough to cool, and then force the solidified sulphur from the gear by pressure of the fingers; this will now be a perfect male spline, which can be used as a grinding jig to produce the shaping tool. It follows then that if the tool is ground up to a perfect mating fit with this male spline, it will shape the crankshat slots to perfection; it is essential however, to mount the tool exactly on centre height. Do not attempt to take more than .002" cuts and work towards the tailstock, roughing out each slot individually at first, and then completing the job by taking a shaving cut off each and every one in turn to ensure perfect dividing.

Plenty of soluble oil or cutting oil should be used during the final shaping operation, and this, together with light finishing cuts, can produce a surface like chrome plate. The method of using sulphur to obtain an exact replica of the inside of a cavity was often used by mould and toolmakers, since sulphur does not shrink on cooling.

The FOWLER crankshaft is much more delicate with its two throws, and the machining will need to be carried out in much lighter cuts. But, if the webs are attempted first, while the crankshaft is stiff, the machining will not present much of a problem. The webs should be milled away early in the machining operations, and the slots end-milled to take the straps for the balance weights. The big end journals of the 2" Fowler are fairly narrow and do not leave much clearance for the turning tool. The cut will normally need to be made in both directions, working towards the steps of the flanges, and overlapping in the middle. Finish by polishing with emery cloth. The Fowler crankshaft is of light section, and will tend to judder when light final cuts are taken on the journals. This juddering can usually be brought to a minimum by dropping the lathe speed until the judder disappears. There can be no doubt that a Fowler shaft can be finished much more easily by grinding than by turning, due to the small width of the journals. When the main crankshaft is completed, mark out the shape of the bob-weights on a piece of steel a little thicker than the finished size of the webs. Then mill or hacksaw the bob-weight blanks, leaving them a little oversize on the curved edge, but being finished to dead size on the angled sides of the weight. Having drilled the necessary fixing holes, bolt the bob-weights onto the crankshaft webs, and then put the shaft up between centres, turning the sides of the bob-weights until they just blend with the main crankshaft webs. After this, with the crankshaft supported on the mainshaft centres, take very light cuts over the outside of the bob-weights using the lathe feed, and gradually machine these down until they are lying on the correct diameter. The splines of the Fowler crankshaft are produced by end-milling slots into the mainshaft and afterwards fitting round-ended keys. Obtain a good sliding fit, and then, after making sure the shaft and the keys are completely clean, put Araldite into the milled slots and press the keys right home; leave for 24 hours for hardening to take place. The keys can be finished by turning over the tops to the right diameter, after which an angle cut right across the rounded ends of the keys will produce the correct Fowler appearance. NOTE ON KEYS It is preferable for keys to be a nice sliding fit, and then to be secured with a medium, such as soft solder or Araldite (the latter being much the easier). Press-fitted keys, in theory, should be permanent, but often, with the oscillating type of strain they receive when working, will loosen after a time. However, keys fitted with some medium become one with the shaft, and are normally quite permanent. The SIMPLICITY crankshaft is short and stubby, so will be quite rigid in the machining. The spline is achieved by end-milling, and inserting loose keys, as previously described for the Fowler. The keys of this crankshaft have dead square ends, and therefore slots should be end-milled and round ended keys fitted; after this the keys will be turned square and will blend flush with the main diameter of the shaft. Always study the drawing of the crankshaft and its gears, since, in some cases, a gear will need to be fitted before the keys are finally secured in place (as the 2" Fowler). To finish the crankshaft after splining and keying has been carried out, it will be necessary to cut the ends to size and face them. A point here:-If the shaft is to be truly authentic, it will be necessary to put centres back into the ends of the mainshaft after the surplus has been machined away.

HARDENING OF CRANKSHAFTS

Hardening in crankshafts is a desirable feature, but unfortunately not easy to achieve at present times. The writer has had many crankshafts hardened prior to final grinding, and this used to be a straightforward job. The process was to case harden, followed by straightening, before grinding. The shaft, after straightening was within .001" to .002" of true. But today, with most firms on mass production, this type of careful job can often go wrong. One-finds, all too frequently, that jobs which were straightforward years ago can now only be carried out at a risk. I personally had one tractor crankshaft scrapped completely in the hardening process; the shaft had been carelessly processed, the result was a shaft that was hard almost completely through, distortion was considerable, and the shaft was out of true by .045" and ultimately broke in the straightening process. The writer does not seek to suggest that hardening of crankshafts is impractical, it certainly is not, in fact if carried out intelligently it is perfectly satisfactory. The modern process of induction hardening, with the parts for heat treatment kept on the move, will keep the distortion to an absolute minimum, but the difficulty lies in the fact that few firms will undertake this sort of work for small numbers or single items. So, if you do decide to have your crankshaft hardened, be very careful where you take it for this to be carried out.

A hardened shaft will last almost indefinitely; the crankshaft on my original model 'BILL' had a surface like chrome plate after seven seasons of use.

A safer hardening process can be carried out on crankshafts. This is to finish your shaft completely, whether it be by turning or grinding; to mark the bearing surfaces (where not obvious) and then to submit the shaft for spraying with Molybdenum. This process is used in the reclaiming of motor car crankshafts and is carried out as follows:-the crankshafts will first be put up on a cylindrical grinder, and the bearing journals will be ground undersize. You cannot do this yourself as it is essential that the metal is absolutely clean and uncontaminated by the atmosphere, therefore this grinding the Molybdenum is sprayed on. Next the shaft is rotated on another machine, and Molybdenum wire is fed into the metal spraying equipment; this melts the wire by oxy-acetylene and blasts the liquid metal straight onto the crankshaft journals. The fine spray is fed along automatically, and is passed backwards and forwards over the journal until sufficient thickness oversize is achieved. This process is carried out on all journals, after which the shaft will be put up again in the grinder and the surfaces ground to dead size. During the process of spraying, the shaft will be protected with tape right up to the edge of the bearing journals. This process is a little costly, but has the advantage that no distortion occurs, and therefore there is no risk; the resultant shaft has hard bearing surfaces with a soft centre. It is claimed that Molybdenum sprayed crankshafts have longer life than straightforward hard steel.

A Molybdenum spray is finely porous and the pores of the metal retain the oil.

Having read the previous remarks on the hardening of crankshafts, it may be that modellers will feel that this is a must for their particular model, but this is not so. A crankshaft made of good quality mild steel, with a good finish (preferably ground) will last a very long time in a traction engine model. The working revolutions of the original engines were only about 250-300 R.P.M. and the reader will appreciate that the lubrication and balance of these engines was such that they were unsuitable for high speeds. There is however, a great tendency with model traction engines to run them at high revolutions, and although a model can comfortably be run at more than the original engines; if high revolutions become a habit in conjunction with non-pressurized lubrication, it will be obvious enough that a soft shaft will soon wear. Therefore it can be concluded that for conditions of reasonable use, a shaft in normal state is quite adequate.

FLYWHEEL

Having made the crankshaft, let us now continue with the FLYWHEEL.

Care should always be taken to machine the flywheel absolutely true. The bore should be a close sliding fit to the crankshaft, so that the two components are true as an assembly. The flywheel of the BURRELL is too large for a ,3f" lathe, and may have to be put out for machining; however, presuming that you have access to a larger lathe, the following hints may be useful.

The builder must aim to machine the complete O.D., the first edge of the rim, and the bore and boss of the first side, in one operation, without removing the flywheel from the lathe. The flywheel can be held on a face-plate, clamped down where the spoke ends are close to the rim, or in a large three jaw chuck. Make sure that the jaws can open up on the inside of the rim, close alongside the spoke ends. If you do not do this, on tightening up, the flywheel will be stretched in three places. While held in the lathe it will be perfectly round, but the minute the chuck jaws are released, the periphery of the flywheel will- be comprised of three bumps and three depressions. The spoked flywheels are the most difficult to set up; care should be taken in holding the work in such a position that the avenge shape of the casting runs true, especially the inner edge of the rim, which will only have a small bevel machined across it to blend with the inner cast surface. It is always good sense in machining any work of this nature to carry out the heavy turning first. This of course will be the O.D., where the greatest strain takes place during the machining. When the heavy machining has taken place, it is extremely unlikely that the flywheel will move in the chuck during the final machining of the bore.

Machining of the rim can be carried out at normal turning speed, using a carbide tool, but more commonly with the smaller lathes, this operation will be carried out in back gear. First turn the rim true across the face until it is on size, after which machine the edge of the rim and produce a high finish, making sure that the spokes end up central in the rim. Now set the top slide over at an angle, so that the inner corner edge of the rim can just be cleaned. NOTE:-This cut should never bite into the inner cast surface of the rim; the angle should be great enough so that it cleans the rim true without doing this. The periphery of your flywheel- will need to be finished in a curve. (This was necessary on the original engines in order to keep the belt on when an engine was working stationary.) To produce the curve by normal turning is virtually impossible. In industry, a curved contour of this nature could be produced on a copying lathe. A lathe can be altered for this purpose, but for just one job it is hardly worthwhile. However, the principle is this:-The lead screw of the cross-slide is removed and a hardened cam follower is attached to the back end of the slide; this bears against a cam plate fixed rigidly to the lathe bed itself. This cam remains stationary as the saddle moves forward, and the follower passes over it. In place of the lead screw, a powerful spring is incorporated, so that the slide can be forced back against the cam. During this operation, the top slide of the lathe is locked to work across the bed, so that the cutting tool can be advanced by this slide, while the position of the main cross slide remains controlled by the cam. Whereas the copying method described may be of interest, there are not many modellers who will feel disposed to convert their lathe for one single flywheel, and therefore a more practical method is described.

The flywheel is already turned to the correct O.D., so proceed to turn four angles on the face of this flywheel, starting from a point just short of the centre of the flywheel and machining outwards to both edges of the rim, but leaving a flat in the centre. For this first angle, three degrees is ideal, after which turn a second angle commencing at a point midway between the centre of the flywheel face and the edge, turning right to the edge again, the angle for this being about five degrees. Since, at this stage, the back of the flywheel has not been machined, it will be possible to machine the angles on both sides of the rim, so that on reversal only the edge is left to clean up. It is important that all the angle turning is carried out at one setting. (See drawing 18.)

Having finished all the angle cuts, turn the centre boss down to diameter, and machine it to length. Next, with a radiused tool ground to the necessary contour, machine the radius where the boss blends with the spokes. For this it is best to run the machine in back gear and remove the bulk of the metal, after which just brush the front of the spokes with the tool and then machine inwards until the tool blends with the diameter of the boss; then drill and carefully machine the boss to dead size. As previously emphasized, the flywheel bore must be an excellent fit on the crankshaft, and if therefore you do intend to use a reamer for the finish, it is best to bring the bore almost to size before putting your trust in the reamer. If you wish to produce an extra tight bore in cast iron, paraffin will help considerably; this tends to make the reamer slide over the work, rather than cut it.

At this stage, the flywheel should be turned over and held again, either in the outside jaws of a large three jaw chuck, or on a face plate, pulling back firmly on to the true edges of the rim. The boss can now be machined in the same manner as the first side, the edge of the rim turned to size, and the angle cut taken, to clean true. The face of the flywheel can be completed by spinning it in the lathe, and using a sanding disc in an electric hand drill. It will now be a simple job to blend in the angle cuts right across the face, ending up with a radius. Finish off with a fine sanding disc; the grinding lines can then be removed by scurfing. Any electro-plater could carry out this final scurfing/polish for you, but should you wish to do it yourself, an old stiff polishing mop can be used; this can be treated with glue and then rolled in emery powder or grit and left overnight to dry.

The FOWLER flywheel should be chucked carefully so that the curved contour runs as true as possible, since it is not intended to be turned. The flywheel rim will be turned in the same manner as for the Burrell, and the centre boss machined and blended to the main web. The non-machined part of the Fowler flywheel can be sanded while spinning, in the same manner as the rim, using a good coarse disc to commence and finishing off with a finer one. (Always protect the lathe bed during sanding operations.)

The spoked BURRELL flywheel and the domed FOWLER flywheel are both very noticeable features, so care should be taken to achieve a high finish. Firstly, remove any raised portions on the casting of the Burrell wheel and blend in wherever possible; after this obtain some coach painting filler paste and blend the casting in where necessary; then rub down with wet and dry paper until the required finish is achieved. The Fowler wheel will benefit from an application of filler all over the outer domed portion of the wheel, and then carefully rubbing down before commencement of painting.

The Wallis and Steevens SIMPLICITY flywheel has a straightforward rim and a plain machined centre with no boss, since it is located and bolted to the web of the crankshaft.

CRANKSHAFT BEARINGS:-Those of the FOWLER have already been discussed in the chapter on hornplates. However, it is sound practice when machining these to leave the bores undersize by a small amount, until they are bolted to the hornplate assembly; this enables them to be finally reamed in line.

The BURRELL and SIMPLICITY roller CRANKSHAFT BEARINGS are similar, in that they are single bearings, and both are machined with a circular step which locates in the hornplates. The bottom half of the bearings should be machined first, holding in a four jaw chuck. Make sure to grip this casting in such a manner that the cast steps will run true before machining. With these bearings, it is often an advantage to put a piece of metal bar across the open end of the bearing, clamping the fourth jaw against this during machining. BURRELLL CRANKBEARING:-After carefully chucking, the hornplate locating step and the face can be trued up to be nearly on size, but not machined completely to size at this stage. The square location for the bronze bearings can now be machined on the face only. Reverse the casting and hold it on the machined flange while facing off the other side of the square bearing location. Next, the slot for the bronzes should be carefully marked centrally using the turned step as a guide from which to measure. It will be possible to hold this bearing in a machine vice, clamping against the machined step or flange, after which the bearing location slot can be machined to the correct depth and width, and the top of the casting end-milled across. Mill the underside of the top bearing cap flat, and to the correct dimension, at the same time, machining them to exactly the same width as the bottom bearings. We will put the bearing housings aside for the moment and machine up the bronzes. Proceed as follows:- Take a piece of bronze (probably a casting) and machine this to clean on two opposite faces. Then saw the bronze in half, cutting through the centre of the machined faces, after which, hold these half bronzes in the machine vice, or in a four jaw chuck in the lathe, and machine to clean up. Garry this out on both halves of the bronzes, after which warm them up with a flame, and tin the two machined faces, fitting them together. (Be sure to heat the bearing sufficiently so that all the excess solder can be squeezed out.) You now have a split bronze, with the split line square to the outer faces.

It will not be difficult to mark out the outer contours of the bearing, and machine these square, and to the correct dimensions, after which the locating slots can be milled all round the bearing, so that they will be a close fit to the locations, in the machined housings. During this milling, your machine vice should be true with the table; it is necessary to clock it before commencing. The bronze should be locked tight against the same face during slotting, so that the four slots will all lie in the same plane, giving the best possible location in the housing. Carefully fit the bronze to its housing, radiusing off corners where necessary, and making sure that the bronze seats right down onto its mating slot. It is usual with these bronzes for them to stand proud of the bottom

housing, so that the bearing top cap can clamp them. When wear takes place, the bearing faces can be filed to compensate for this, the cap can then be tightened down without bearing on the bottom half of the casting. Next mark and drill the clearance holes for the studs in the top caps of the bearing, and with the bronze in position, it will be possible to locate the top cap in the bearing slot, and use this assembly as a jig in order to drill through for the studs in the bottom half of the housing. Hie bore of the bush will now need machining, and for this, the top cap must once again be removed and replaced by a small piece of bar; very carefully locate the casting as square as possible to the lathe bed, and hold it so that the hornplate location step is as true as possible. After this, lock the chuck up tightly, and machine the locating step to exact size, also skimming over the faces. (Remember that these were left oversize.) Now face off the bearing bronze to the correct flange thickness, and then drill and bore, aiming to leave the finished bore a few thous. undersize. After this is completed, remove the bearing from the chuck, fit the top cap, and tighten down. Turn up a suitable spigot to locate the bore, and reverse the casting onto this, so as to face the other side of the bronze bearing to final width. The oiling for these bearings is by wiek feed, so to complete the unit it will be necessary to end-mill out the little oil boxes, after which drill a hole through the casting and the top bronze, fitting a small copper tube to take the wick. The lid of the oil box can be made from a piece of brass sheet; a small hinge flap can be fitted, to soft solder to the inside of the box to complete the job. The pair of crankshaft bearings are now complete except for the bores, so drill the flanges and bolt these to the horn-plates, and make a suitable long reamer to ream the bores in line. You could make a 'D' bit, long enough to pass through both bearings, or take a standard length reamer to which an extension has been fitted. Whichever way it is done, the shank will need to locate first in the undersize bore, while the reamer brings the other side to final size, and then in the finished bore, while reaming the second bearing in line. Next dismantle the bearing and warm up the bronzes until they can be parted when the solder melts, clean off the faces and the job is complete.

The WALLIS & STEEVENS SIMPLICITY roller, crankshaft bearings are very straightforward. The milling on

the bottom and the top of the bearing housings is best carried out first; then the two components can be fitted together. The cap extension should be a nice sliding fit in the slot in the bottom bearing. Drill and tap for the two studs, after which a shim should be put between the top cap and the bottom, so that the two halves of the housing will eventually be able to clamp down on the bearing bush. The circular locating steps can now be machined on the first side of the bearing, but be sure to hold the casting so that it is square and true before machining. Now machine the bore to final size, reverse onto a spigot and complete the second side. The crankshaft bearing bronzes of the Simplicity are circular, and in one piece, being blind at the outer end, presumably for safety and to exclude dirt. The bushes are simply put into the housings and clamped tight Oiling is achieved by an oil cup which screws into the top cap of the bearing, there being a hole passing through the cap and the bronze bush.

ECCENTRICS AND SHEAVES:-The Simplicity eccentrics are straightforward, since the sheaves (or straps) are finished with a plain bore; this runs in a turned groove in the eccentric. The strap castings should be cleaned up on one side and marked and drilled for the bolts. After this the casting can be cut in half and the mating faces machined flat, before bolting together again. Now locate the flat surface on the faceplate, and carefully machine the face and the bore, so as to leave the bolts central in the finished strap. After this simply reverse and machine the second side to the final width. BURRELL and FOWLER:-The design of the eccentrics on the original engines was evolved through experience. In the good old days engines were built to last almost for ever, so let us be guided by the old masters. One often sees short cuts taken with eccentric design. Certainly it is impossible, in a plain bearing, to improve on a design which kept the eccentric straps in line, and had the bearing across the total width of the face. Let us therefore, not be slapdash about the eccentrics, or be put off by the inaccessible recess in the straps. The straps will be produced in the same manner as for the Simplicity, the only basic difference being the bore. This can be machined by setting the top slide across the bed for sensitive indexing. Then with a short boring tool holder, use a finishing tool ground up to the shape of a narrow parting tool, but with a slight difference. (See drawing No. 19.) First rough out the groove and then carry out the finishing cut to the bore with the top slide set at zero position. Advance this slide to the required tool depth to finish the inner face of the groove. Face off each end to final width and the job is done. Since the spring on the tool is constant for both the inner and outer bore diameters, it follows that the groove should be of the exact depth that the feed dial indicates. ECCENTRICS on models are usually fitted with a locking screw in order that they can be adjusted. The BURRELL reverse eccentric will need to be adjusted first, since this is press fitted to the eccentric hub, both moving together on adjustment, whereas the forward eccentric is adjusted as an individual item. Adjustment of eccentrics is very desirable, and can be carried out much in the same way as adjusting the ignition of a car; advance the valve opening to a point at which the flywheel will start to kick back when it is turned over to run; after which the eccentric can be turned back very slightly, and then locked up permanently. The procedure is the same for the FOWLER SHOWMAN compound, carrying out the adjustment first on the high pressure cylinder, and then on the low pressure cylinder for forward motion, and then cany-ing out the same procedure for reverse. The FOWLER ECCENTRICS themselves need a good deal of care since they are split. An ideal way to make these is to take a piece of steel plate of the correct finished width and rough turn circular blanks; after which cut in half, face, and bolt them back together again (as drawings). Now drill an undersized hole through the eccentric, and chuck a piece of steel rod in tiie lathe, face the end, and drill and tap for a stud. The eccentric blank can now be pulled back against the turned face and locked, using a nut and stout washer. Turn the O.D. of the eccentric and the two side steps to finished size (see drawing No. 19). When all the valve eccentrics have been finished to this point, carefully locate them pn the lathe faceplate in order to bore their centres to finished size; for this, bolt two pieces of flat steel to the faceplate against the eccentric. The idea is that when you clamp the next eccentric in place it will be located against these strips, and will ensure that each eccentric has an identical throw. This same procedure can be used on the Burrell valve eccentrics. The eccentric rods themselves, for any engine, are always best left until their length can be checked on assembly. See VALVE CARRIERS (centralising of valves).