Camshaft (Cam)

A camshaft is a shaft with oval or egg-shaped lobes, called cams, that open and close the intake and exhaust valves of a four-stroke engine. It is driven from the crankshaft by a chain, belt or gears and turns at half crankshaft speed, because each valve opens once every two crank revolutions.

Engines may have a single overhead camshaft (SOHC), two overhead camshafts (DOHC) or a camshaft in the block with pushrods, as on many classic V-twins. The shape of the lobes – lift and duration – largely decides where in the rev range the engine makes its power.

Worn cam lobes, a stretched cam chain or wrong valve clearances cause ticking noises, poor running and lost power. Check valve clearances at the service intervals and use the oil grade the manufacturer specifies.