Overhead camshaft

(OHC) The camshaft that activates the valves is mounted above the head and driven by a long timing chain or cam chain. In contrast, a pushrod engine has the camshaft below the cylinders so that thin rods (pushrods) are moved by the camshaft and activate the valves. An engine with an overhead cam means that the distance between the cam and the valves is much shorter, so the valves respond quicker and valve adjustment can be more accurate. Also this system allows for higher engine speed because of fewer moving valvetrain parts. A system with only one cam is called "Single Overhead Cam" (SOHC). In some instances there are two camshafts above the heads (one for the intake valves and the other for the exhaust) and called "double overhead cam" (DOHC). See single overhead camshaft, twin overhead camshaft