Rotating shaft used to push open valves at the proper time in the engine
cycle, either directly or through mechanical or hydraulic linkage (push rodsrocker arms, tappets). Most modern automobile engines have one or more
camshafts mounted in the engine head (overhead cam). Most older engines
had camshafts in the crankcase. Camshafts are generally made of forged steel
or cast iron and are driven off the crankshaft by means of a belt or chain (timing chain). To reduce weight, some cams are made from a hollow shaft with the cam lobes press-fit on. In four-stroke cycle engines, the camshaft rotates at
half engine speed