“HOTTING-UP” A STANDARD MODEL FOR COMPETITION WORK. (PART 1).
Practical Suggestions for Increasing Car Efficiency.
IF the title chosen for this article has an ungrammatical flavour, I think readers of THE BROOKLANDS GAZETTE will pardon the expression ” Hotting-up,” as it most aptly describes the results obtained by the kind of attentions required to bring a car up to the stage of mechanical efficiency that gives its owner every confidence in entering for the various competitions, which hold so remarkable a fascination for the enthusiastic motorist.
In the issue of August last year, I had the pleasure of contributing an article on the ” vetting” of a sporting car, but as the information contained was necessarily abridged, it is now proposed to go rather more fully into the subject and to describe the exact methods to be followed by the car owner who has the ability and necessary facilities for carrying out the work on his own account.
We all know the difference between handling a car in a competition, prepared for the event by somebody else, and the feeling of satisfaction that exists when the entered machine has been brought up to concert pitch by our own efforts. As a matter of fact, the cornpetitor who enters a comparatively old car, which he knows from the front spring greasers to the rear number plate, has often a far better chance of success than the person who rushes in at the last moment with a supersports car, delivered but a couple of days before the critical event.
Then again, the super-sports car is not everybody’s machine, and many of us who use cars for business purposes or ordinary touring have to be content with a more or less standard model to carry us through the daily routine as well as for such competitions as may excite our interest.
Before deciding as to the methods of ” hotting-up ” to be adopted, it is important to make sure that the car falls within one of the standard categories regulating the entries for competitions, though of course there are certain events of a sufficiently severe character where such limitations do not apply.
As far as my own personal tastes go, I always find a great deal of amusement in experimenting with some type of car from which one does not expect to find anything extraordinary in the way of performance ; for provided the car is of reasonably good design and possesses substantial constructional features with ample factors of safety in all parts of the mechanism, one has a fair amount of scope for turning an ordinary touring model into something approaching a. car of superperformance.
” Hotting-up ” Time.
Possibly the present time is as convenient as any for commencing work to prepare the car for the season’s competitions, and many owners make a point of putting their cars into dock after the London-Exeter, in order to treat them to a really first-class overhaul in readiness
for the Land’s End trip. Work of this kind should never be hurried, and needless to say the closest personal attention is necessary at every stage of the proceedings, for many of the processes are simply elaborations of those which characterised the best built cars before the’ era of mass production and keenly cut initial costs came into vogue.
In order to carry out the whole business in a methodical manner, the aspirant to competition honours should make it his first objective to discover the best performance of which his car is capable before any work is commenced. One of the most useful of tests is to take the car to a really stiff hill and observe the speed attained at various points in the ascent. As the surface of some of the well-known ” stunt ” hills varies from month to month, it is preferable to select a main road, or secondary road gradient, so that comparisons may not be rendered futile by possible variations in wheel grip.
If the car boasts a reliable gradient meter, the instrument can be used to record its accelerating capabilities, as well as the actual gradients over which the tests are being carried out. There are several other accessories that can with great advantage be added to the superstandard model for use in competition work, but for the moment we will confine ourselves to mention of the gradient meter, by the aid of which it will be possible to obtain sufficient data of car performance to serve as a starting point for the “hotting-up ” processes.
Hints on Dismantling the Engine.
The limitations of working space in the private garage may prompt the car owner to attempt a partial overhaul of his engine without removing the entire ‘unit from the chassis, and in such a case he will be working under a very great disadvantage, for whilst it is possible to undertake such jobs as adjusting a set of big-end bearings from beneath the car, a complete overhaul cannot well be effected under such conditions. The first thing, therefore, will be to remove the engine bodily from the fromeiand mount it on a suitable trestle upon which the remainder of the dismantling work will be done.
Some amateur mechanics make a practice of doing as much work as possible single handed and getting “casual labour” when additional help is needed ; but if one is fortunate enough to be able to call upon the services of a fellow enthusiast—one’s observer, for example—not only will the job be done very much quicker and better, but there will be the companionship, which counts for so much during long hours spent in the workshop. I need not take up useful space in discussing methods of dismantling the engine, but will pass on with a few observations. Firstly, the engine must be taken to
pieces entirely, and during the process, figure stamps should be used liberally to mark the positions in which various components are fitted. (This will save a lot of trouble in the subsequent re-assembling). Then as the process continues it is a good plan to locate all bolts in their proper places as far as possible, in preference to throwing them all loosely in a box from which they would have to be sorted out later. This advice does seem elementary I admit, and yet how many experienced mechanics can recall hours of valuable time wasted simply because untidy methods of engine dismantling have been practiced. At the same time, there will be an opportunity of examining the condition of all engine bolts, particularly those subjected to stresses such as those holding the halves of the connecting-rods together. Just before the London-Exeter, I discovered a badly stretched
bolt on one of my connecting rods, and an extra pull on the spanner caused it to break in two, which would have made a nasty mess of the whole engine had it not been discovered in time. The first indication of a stretching bolt is the buttress shape assumed by the threads and when this stage is reached the bolt is unfit for further duty.
Assuming that our engine is now carefully dismantled and that all the component parts are arranged for inspection, we may now begin the important business of providing for a perfect balance, which is absolutely essential to secure the maximum ” revs.” and sustained power output.
Testing the Crankshaft.
A rough and ready test for accurate alignment of the three bearings of a four-throw crankshaft consists in laying the shaft in the two end bearings, with the centre one removed. By fixing a small scribing block on the
centre web of the crankcase, the pointer is arranged to fall over the centre journal and by turning the shaft slowly, it can be seen whether the journal runs concentrically with the other two. If at any point of the revolution the journal falls away from the scriber by as little as 0.003 in., it will be impossible to fit the main bearings accurately so as to prevent periodic vibrations of the engine. Further accuracy in testing the crankshaft is possible by using the simple contrivance illustrated in Fig. I, which comprises a substantial piece of channel steel A, cut away at the base as shown, with a machined upper surface. Two solid steel Vee blocks B, are used to support the crankshaft to be tested and a scribing block is used as in the previous case. This simple appliance has the advantage of permitting the shaft to be trued if any discrepancy exists, for by means of the stiff clamp,
shown in the illustration, pressure can be exerted on the centre journal to spring it back into line with the others. (See Fig. z). At first sight, it may appear that this is somewhat of a crude method for dealing with crankshafts, but it all depends how the process is carried out, and a person of average skill can achieve satisfactory results by working methodically. Let us assume that on testing the shaft it is found to be out of truth to the extent of say, o.o05 in. at the centre journal, this dimension having been measured by inserting a five ” thou ” feeler between the point of the scriber and the journal at the position where the eccentricity is greatest. We now have to spring the shaft in the opposite direction by means of screwing down the clamp screw and in doing so the scribing block is used to determine the amount of counter distortion required to remedy the defect. Here is where the trial and error process comes into play and for a start we will exert sufficient pressure
on the screw to spring the shaft to the extent of 1-32′ to overcome the natural elasticity of the metal.
On releasing the clamp, the scriber is again applied to the centre journal for a further check, and it will be observed whether the eccentricity is increased or diminished. This will give an indication as to whether the counter distortion has been correctly estimated and the process must be continued until the journal is found to be in accurate alignment with the other two.
A Simple Crankshaft Balancer.
The problem of ascertaining whether the crankshaft itself is properly balanced, presents something of a difficulty to the amateur mechanic, but by the exercise of a little ingenuity it is fairly easy to construct a suitable device for the purpose in the home workshop. What we require is some means for supporting the shaft whilst
it is revolved at a high speed, the supports being so arranged that they will vibrate unless the crankshaft has no unbalanced masses.
The use of ordinary Vee blocks creates too much friction and therefore some other method must be adopted. Fig. 3 illustrates a fairly simple contrivance, which consists essentially in a pivotted support, with a double fork at its upper end, in which two knife-edged hardened rollers are mounted. This support is surrounded by a metal cylinder, the space between the support and the inside of the cylinder being filled with rubber crepe, A. Two of these devices will be required to take the place of the Vee blocks upon which the shaft will be mounted for the balance test, and the shaft is made to revolve rapidly by means of a rubber belt on its centre journal, the movement being provided from a pulley on the overhead shafting of the workshop.
Immediately the shaft is made to revolve at a high speed, it may be that the supports will vibrate considerably, and it will be found that by attaching small pieces of lead to the webs with insulating tape that the vibrations will either increase or diminish, the experiments being continued until the correct disposition of the weights has been found to create a vibrationless motion. The final part of the job consists in removing the required amount of metal from the webs, opposite to where the weights have been attached, until a perfect balance is secured.
The final attention to the crankshaft before one commences the work of re-fitting the bearings, consists in trying the big-end journals for wear. This is done by means of a micrometer calliper gauge, careful measurement being taken at various places on the journal to see that there is no ovality, such as would prevent a good fit for the connecting rod bearings. If a discrepancy to the extent of a couple of ” thous ” is detected, the journal can be restored by careful filing, using the micrometer gauge at frequent intervals as the job proceeds. The final stages should be performed with fine emery cloth, so as to remove all traces of the file marks and a specially made lead lap will be needed for the finishing touches to provide a smooth and regular surface for the bearing.
In view of modern repair shop facilities, one may ask why it is recommended that the owner mechanic should take all the trouble to carry out this kind of work himself ; but I think if one enjoys the advantages of his own workshop and a reasonable amount of leisure, half the pleasure of competition work consists in bringing the car up to scratch by personal efforts, such as those described above.
In my next article on this subject, I propose to deal with some of the niceties of bearing fitting and explain how many of the faults, common in this very important part of engine work, may be avoided.
(To be continued).
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