Abstract
During the last few years the cam-tappet problem has become very important because of the continuous increase in the maximum rotational speed of engines for the purpose of increasing power. This necessitates the overloading of the springs in order to offset the inertia effects of the distribution system as a whole; the result of this is to increase the specific pressures of the cam-tappet unit. As the present tendency is to make engines revolve at ever greater speed, it is to be expected that the problem of the behaviour of these components in service will be more and more difficult to solve.
There is no doubt that the ideal solution lies in decreasing the inertia forces by giving up the rocker system, and using the arrangement of the overhead camshaft acting directly on the valve stem.
For engines with the traditional system of valve action by rockers, the problem of the deterioration of cams and tappets has been studied by Simca on a specially designed testing machine. The laboratory tests thus made have been followed by tests carried out by the Shell Company on engines on the test bench. The present paper sums up the results obtained.
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