A Camshaft is a shaft containing lobes (also called cams) which is synchronised with the crankshaft. Its function is to rotate and open and close the valves in the engine. Camshafts may be located on top of the heads of the engine (SOHC or DOHC) or near the crankshaft. When the camshaft is located near the crankshaft, its rotation causes its lobes to press on pushrods which extend to the top of the engine and connect to rocker arms which then open and close the valves. Harley-Davidson motorcycles are heavy users of the pushrod method of valve operation. (Also referred to as cams)