Order to avoid the necessity for frequent adjustment of the earlier type valve clearances, new designs of valve lifting cams were later adopted in practically all engines, to allow greater clearances to be used, without additional valve noise or power loss.
For modern engines of both side and overhead type valve clearances range from the most widely used clearances being. With these clearances it is unnecessary to adjust the valves, make certain that these refer to the engine in the hot or cold state, since there may be a difference of between the two valves.
The valve tappet clearances is tested with a thin metal strip of the correct thickness, inserted between the valve and its tappet or rocker arm. The “feeler” gauge arranged in steel strips of multiples of one-thousand the of an thick, as used by engineers, is the best device for this purpose.