MOTORING

Progress, Volume X, Issue 6, 1 February 1915, Page 213

MOTORING

By "SPANNER"

A Matter of Compression Modern cars do not often suffer from too high a compression, at any rate when they are new or clean internally, as makers will go to a deal of trouble to ascertain the highest ratio which their engines will comfortably stand. Some three years ago, however, the writer had a great deal of trouble with an engine which had really too high a compression, and the overcoming of the ensuing trouble proved very interesting. The car was very fast, but did not climb particularly well, for the engine got too hot, and very soon began to knock on a stiff gradient, even with the ignition well retarded. • When standing, the engine turned over in a very irregular fashion, and would not run really slowly. Ignition, carburetter, and valves were overhauled, but all to no purpose. The car was then returned to the makers, and they effected a slight improvement, which, however, disappeared in the course of a few weeks. The makers had two more trials, but without permanent effect. It was then noticed that the rate at which carbonisation was set up was extraordinary, and that possibly the amount of deposit on the piston top and cylinder head might be sufficient to increase the compression ratio to such an extent, that it was considerably affected. It was resolved to test this supposition. The valve caps on the engine were of a generous size and unusually deep. Four iron washers were turned up a quarter of an inch deep, and one was inserted beneath each exhaust valve cap. The effect was magical. The engine would then tick round at 120 to the minute, and the car would climb hills without a sign of a knock, even when the gradient forced the engine to its last gasp. The same still applies, and it no longer overheats or selfignites, and carbonisation is no longer the bugbear it used to be. In every respect the engine is more pleasant to drive. When the cylinders were next taken off, fibre washers, about 1-32 inch in thickness, were placed between the cylinders and crank case, and the iron washers beneath the valve caps could then he dispensed with. No one who has not made such experiments, can realize what a tremendous difference or improvement can often he effected by a decreased compression. It is obvious that the stress on the bearings is much lessened. As a matter of fact, the engine in question after the alteration, ran 15,000 miles without having the bearings attended to, though in the previous six months the whole engine had been taken down twice and overhauled by the makers. The speed of the engine was not decreased to any appreciable extent. Acceleration was slightly better, and consumption showed a small improvement. The worst thing about the loss of a Turkish soldier is that it causes so many widows.

The Clutch Stop A large proportion of modern cars are constructed without any stop or anti-spin device on the clutch, the makers apparently relying on the exhibition of skill on the part of the driver to avoid any noisy gear change. While it is impossible to generalize on a matter of this kind, we must confess to a rather blind faith in the efficacy of the clutch stop. True, many cars get on well enough without it, but all the same the inclusion of it is a more positive way to get good results. As long as a car is new and in good order, with well-shaped teeth to the gears, changing is not so very difficult without a stop. But it is when some of the components have become worn, when the clutch disc spins, not light and free, but with a persistent motion, it is then that a clutch stop is essential. Wear on the spigot end of the crank-shaft or the socket bearing of the clutch and disc, or, again, non-adjustment of -the multiple-type of clutchany of these interfere with the original sweetness of gear-changing on a car. It is rarely difficult to devise a clutch stop, and any intelligent mechanic should be able to make and fit one with a few hours and at small cost. It should be so arranged that for changing down—when the stop is not wanted— does not come into action. In other words a full down-thrust of the clutch pedal should be needed before the stop is reached.