FOR THE AMATEUR
The Owner’s Workshop
EVERY owner of a sports car fancies himself to some extent as a mechanic and is desirous of turning what ability he has in this direction to good account. Previous articles of this series have dealt with some of the necessary but not very exciting tasks, which have to be carried out from time to time if a motor car is to remain safe and pleasant to handle.
When these have been attended to we come to the great question of how to get the best out of the engine, and I must crave the indulgence of our more technical readers if portions of these remarks appear terribly elementary. It often happens that, as Will Shakespeare so aptly puts it, “desire doth outrun performance,” and there is always a certain proportion of owners whose enthusiasm is out of all proportion to their mechanical knowledge. Therefore I suggest that those for whom the internal combustion engine holds no mysteries should pass on to some other part of MOTOR SPORT.
The overhaul of a modern motorcar gives almost unique scope for starting the job at the wrong end, and most amateurs are quick to take advantage of this, and do all the wrong jobs first, and leave the important things undone.
In most cases tuning is started on a vehicle which has a fair mileage to its credit, as when an engine has been really fully run in the best results can be obtained. Also in the case of the less wealthy owner, the tuning is usually combined with the normal overhaul necessary to get the vehicle in sound condition for a season’s running.
It is not proposed to deal at present with what is generally referred to as ” super-tuning,” or, getting just as much power as an engine will give without going up in smoke, but rather with getting a reliably quick performance from a normal sports engine. What is necessary, however, is to dispel the popular fallacy that ordinary tuning is a matter of waving a
ENGINE OVERHAULS AND GENERAL TUNING.
magic wand. One still comes across the pest who offers to infuse ” pep ” into the engine by playing with the carburettor or ignition timing, regardless of whether that is the trouble, and usually with very poor results. Carburation and ignition come among the finer points of tuning, and must be left to the end.
The first essential is to get the engine in perfectly sound mechanical condition, and it is in this process that various refinements can be added to the normal routine, such as balancing. The extent to which these refinements can be indulged in will depend chiefly on the depth of the owner’s pocket, and will have to be left undone in inverse proportion to this important dimension. In the actual matter of fitting, assembling, etc., there can be no question of leaving things undone, however. It is this capacity for taking time and trouble over seemingly minor details, that distinguishes the good fitter and tuner from his more slapdash, and consequently unsuccessful brethren.
It is obviously impossible to give detailed information for the treatment of every make of engine, and the actual details peculiar to any particular make must be filled in from the owner’s experience or inspection of the machine concerned. We can imagine the engine to be of the normal four or six cylinder type with valves operated from a camshaft in the crankcase. The procedure with an overhead camshaft engine must be dictated by the intelligence and observation of the operator. We will assume that the engine, after being run in with reasonable care, has had a considerable amount of hard work, and it is now intended to get it in thoroughly good fettle for fast road work and competitions.
Although the usual routine top overhauls are always done with the engine in the chassis, for a complete overhaul the engine should, with few exceptions, be removed from the chassis. It may seem that this means a lot of work, but it will be found that in the end time will be saved and the job will be done better. In the case of fairly small engines—round about the I i-litre class—it is not difficult to get the engine out and onto some sort of improved stand, such as a strong wooden case. As the majority of home-tuned engines are in the smaller classes, it is these that have to be considered. The actual process of disconnecting gear-box, transmission, pipes, leads, etc., will naturally vary for every car, but is as a rule fairly obvious. The radiator will have to come off, and special care should be taken to see that any packing, such as rubber, used in the mounting of it, is preserved in good order or replaced with new if necessary. If care is not taken in refixing the radiator, the owner will be to blame if any leaks develop.
In the actual removal of the engine a lifting tackle as described in MOTOR SPORT for last February is extremely useful, especially if help is not easily available in the actual lifting. However, the lack of tackle should not deter anyone from removing the engine, and many people scorn the assistance of anything but their own strength on such jobs. The task is made considerably easier if the engine has a detachable cylinder block, as well as the head. In this case the head and block can be removed first with the engine in situ, and the remainder of the engine can then be lifted out much more easily than the complete outfit. Care is needed in actually lifting off the block to avoid the pistons falling against something hard and getting damaged. This is most liable to happen when standing on the chassis and lifting the block vertically. If this procedure is adopted It is advisable to have a friend standing by.to catch the pieces ! On a fairly light
THE OWNER’S WORKSHOP—continued.
engine the block can be drawn off on one side so as to leave the rods all leaning against the side of the case. A great many engines nowadays are made with the cylinders and crankcase cast together, in which case the best procedure is to remove the engine complete, take off the sump, and place the engine upside down on the engine stand. If the valves have been previously removed it will then be unnecessary to move the engine again until the overhaul is completed, as all main bearing fittings, etc., can be done in this position.
The extent of the dismantling of the lower part of the engine will depend On the owner’s desires in the way of performance, but assuming that he is going to make a job of it, the next consideration will be the balancing of the crankshaft, flywheel, rods and pistons. Getting the best out of an engine is mainly a question of patience and hard work, and this balancing and refitting business cannot be rushed.
One of the most important things to look out for in this class of work is to have some good system about storing the dismantled parts. Have a good supply of boxes for the parts, and avoid getting them mixed up. Anyone who is really neat in this department is likely to be a fairly good mechanic, and he will certainly save himself a lot of time. A set of number punches is a very useful accessory, and all parts such as con-rods, valves, pistons, etc., should be numbered immediately on removal from the engine if they are not already marked. They should also be marked in a uniform manner so that everything will be put back the right way round.
Timing Marks. the it is
Before removing the crankshaft it is as well to see if the timing wheel teeth are, marked in any way, and if not, to mark two adjacent teeth. A dab of white paint is a most effective method of doing this, as punch marks do not do the teeth any good. If the drive is by chain some other method will have to be thought of, such as marking the sprocket teeth opposite to each other. The main and. big end bearings should be examined for wear, and the crankshaft
journals should be checked for ovality. This is most liable to occur on the crankpin journals, and a micrometer should be acquired or borrowed to check this. A micrometer is not an instrument which is in constant use, but it is nevertheless something that every mechanic should understand and be able to use. If the journals are .002″ or less oval they can well be left and the bearings refitted op them. If they are badly oval, however, it is impossible to make a safe job of the bearings and the shaft should be sent to be reground by some firm who specialise in this work. Now that the shaft has been removed it is worth having it checked for balance, and the flywheel should be balanced hidependently at the same time. This is well worth doing as it will be done once for all (unless the crankshaft breaks !) and the improvement in smooth running
and increased r.p.m. will be well worth the cost. It is not a job which can be done at home, however, as to get the shaft statically balanced is not enough. It must be set up in a dynamic balancer and tested for vibration at various speeds. This requires special apparatus and skilled operators.
When the shaft and flywheel are returned for reassembling the question of bearing fitting comes up. The first thing is to make sure the main bearings are O.K. In the case of a 3 or more bearing shaft, perfect alignment is of course essential, and this means that all the bearings have got to be fitted together. It is no good scraping in, say, the front bearing and completely fitting it, and then going on to the others in turn. This is liable to cause binding through bending of the shaft, when the actual clearance on individual bearings is sufficient.
Therefore, the correct procedure is to bed the shaft into the top half of all bearings in the crankcase, until it lies in perfect contact with all of them, and then fit the bearing caps without again touching the other halves—except of course to wash them clean before bolting up. None of these remarks apply to ball or roller bearing shafts of course, but as these are in the minority a few remarks on the actual procedure of scraping in a white-metal or bronze bearing may not be out of place. Some bearings consist of white metal poured direct into the bearing and then bored and split. In others the “
brasses” consist of die cast white metal liners, the halves of which are fitted into the bearing caps, while the commonest variety consists of bronze machined shells into which white metal has been run, and these are fitted into the bearing caps. The first mentioned type is the best in theory as almost perfect contact between the metal and the connecting rod or bearing housing is made, and this helps the heat flow away from the bearing under heavy loads, and so reduces risk of failure. The last type is extremely convenient
for replacement purposes, is mechanically strong, and much in use. The other type is weak and liable to break up, has very poor contact for getting heat away, and has nothing to recommend it except that it is cheap to make. The bronze white-metal type of bearing requires a little more trouble in fitting
than the others but the method is similar in all cases, and it will be obvious which steps can be omitted with different types.
The first thing is to get the brasses to fit correctly in their housings. This may occasionally require a little attention with a file or scraper, though on most makes the spare parts fit fairly accurately these days. The chief points to be looked for are to get the edges of the brasses perfectly flush with the edges of the housing, so that when the halves are bolted up there will be no gaps. The brasses are sometimes too long for the journals, and if so, will require filing at the ends to obviate this. Files have to be used extensively in fitting work, and nothing but practice will help to make the operator good at their use. Filing ” square ” is difficult and requires skill and patience. The great thing to remember about filing is that it is a cutting, not a rubbing process. Therefore slow steady strokes in a forward direction only must be used, with enough weight on the file to make sure it is cutting. The work should be as nearly as possible at elbow level as this makes it easier to achieve a flat surface. Having fitted the halves of the bearing correctly into the housings the scraping in process must be started. This is necessary as bearings are always finished off too small for the journal to allow for fitting. In building a new engine it is possible to machine the bearings to the correct size and fit without scraping, but for supplying as spare parts such a proceeding has considerable drawbacks owing to the fact that the journal may be worn, or may have been reground. There is a prevalent idea that hand fitting of a bearing is the best method. It is not, but it is the only
THE OWNER’S WORKSHOP—continued .
method possible in replacement work, and therefore it must be practised until it can be carried out as nearly perfectly as possible. A hand scraped surface will not be as accurate as a machined surface and the ideal bearing (of the plain variety) would be one which is machined to exactly the correct size, i.e., a clearance of say .001″ for oil on a normal 1500 c.c. crankshaft and fitted without further touching of the surface.
However, this being outside present possibilities for replacement work, the only course is to hand fit the bearings. This consists of “offering up” the parts, finding where the metal touches the shaft, and removing metal with the scraper until it is touching all over. At first the bearing will bind at the edges of each half, and, as these are scraped will settle down to a good fit. Red lead is the normal compound used for seeing where the bearing is making contact.
This should be smeared very thinly on the journal before trying it each time, and after it has been assembled and bolted up just tight enough to make the shaft stiff to turn, the marks will be clearly left on the bearing, showing where the metal must be scraped away.
It is impossible to get universal contact by hand fitting, but it will soon be seen when contact is being made at the different parts of the bearing, and to what extent, so that as the process is continued the contact surface will develop from the mere” pinching” at a few spots, to fairly general contact. Local “high spots” can be detected by the appearance of the marking as it will be blackish and polished, instead of merely showing the transference of red lead from journal to bearing. The process of marking the shaft, fitting, bolting up, turning, unbolting and scraping the bearing where indicated, has to be oft repeated before the desired result is obtained, and considerable patience is required.
The actual bedding down of the main bearings is the most tedious part, especially in a 3 or more bearing job, but in the first stages of this it is not necessary to bolt up each time, as the merely laying on of the shaft and turning will mark the halves of the bearing until fitting is nearly finished. When these upper halves make good contact on all bearings the other caps can be applied. When good bearing surface has been achieved on both halves the bearings are ready for final assembly, but it will now most probably be found that the tightening down of the bolts will lock the shaft up too tight in the bearings. It is here that provision must be made for taking up wear in the future, and shims must be fitted between the bearing halves to give the necessary clearance. It is, of course, absolutely essential that all bearing bolts should be done up dead tight, and any attempt to adjust the tightness of a bearing by slacking the nuts even a fraction of a turn will be disastrous. If when the nuts are tightened down the bearings are still too tight,
another shim on each side must be inserted.
These can be bought cheaply for the better known makes of cars, but in any case they can be easily cut out of brass foil with a pair of scissors. A few small sheets of foil of varying thicknesses should always be kept handy, the thinnest being about .002″ thick. This can be used for final adjustment.
It has been assumed so far that new bearings are being fitted throughout, as this is the biggest job. If, however, the old bearings are in good condition and free from cracks or bad scores, they can be taken up by removing some shims, and scraping in the same manner as described above. When no shims are used, and it is required to take up the bearing it will be necessary to take each surface down with a fine file or emery cloth on a file. This requires very great care to keep the halves square with each other, and unless you are really skilful with these implements It is better to leave well alone, and fit new bearings and shims. There is a lot of argument about how tight white metal bearings should be fitted, but it really depends on how accur
ately the scraping has been done. If the bearing is touching over its whole surface, it can be fitted so that it is free at the start, and will not get any looser in settling down. If, however, contact is only made at a few points, these will soon get crushed flat or rubbed away, and the bearing will soon be loose even if it felt tight when put up. No scraped bearing gives perfect contact, but if well fitted need not be put up very tight. In the case of big end bearings a rough test may be made by seeing if the rod, without piston, will just “stay put” when swung out to a horizontal position when the bearing is bolted up dry. From the feel of this stiffness, the correct fitting for the crankshaft can be gauged from the number of bearings and the feel of it. In fitting the big ends with the crankshaft out, one end of the shaft can be supported in the vice, while the other can rest in a V-notch in the end of a board whose other end rests on the floor. The whole business of fitting bearings requires time and patience, but if the fitter gets tired of fitting a 3-bearing shaft, let him try fitting a complete new set of bearings to a six-cylinder seven bearing crankshaft I
Having got the main and big end bearings ready they can be finally assembled with oil. It will be simplest to fit the pistons at the same time, even if the cylinder block is separate from the case, as it is easier to do these individually than to lower the block on to the whole set at once. If, however, the total weight will then be too much for easy refitting of the engine the block will have to be left off till later. Naturally there will be a lot of work to be done to the upper parts of the engine, and in the next article of this series the treatment of these parts, also valves, etc., will be discussed.
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