All About Engines

210 All About Engines . VALVE Fig. 119.—Adjustable valve tappet the engine it passes through a great length of tubing called a radiator, in which it is cooled. The cooling effect is greatly increased by thin “ fins ” fixed to the tubes, and / offering a large surface to the air. The piston is of the trunk type. The connecting rod is of steel, and is of such a form as to give the requisite strength with maximum light- ness, and the valves are of the mushroom type, held down on their seats by springs and lifted by cams fixed on a rotating shaft or shafts as shown in Fig. 119. The tap- pet lifter, between the cam and the valve rod, can be altered in position as the end of the valve rod wears. The cam shaft is driven from the main shaft by toothed wheels or by a chain, and turns at half the rate. Origin- ally the inlet valve was not operated by a cam, but was held down by a rather weak spring and opened by suction of the engine. The cylinder is bolted directly to the crank case, which may be of thin malleable iron or aluminium alloy. Oil is supplied to the rub- bing surfaces by a pump and flows into crank case.