According to the number of camshaft, can be divided into single overhead camshaft (SOHC) and double overhead camshaft (DOHC) two. Single overhead camshaft is only one camshaft, double overhead camshaft is two, which is too straightforward explanation.

Single overhead camshaft with a camshaft cylinder head, direct drive into the exhaust valve, it has a simple structure, suitable for high-speed engine. In the past generally used side camshafts, camshafts on the cylinder side, the timing gear directly driven. In order to change the rotation of the camshaft to the reciprocating movement of the valve, the valve lifter must be used to transmit power. In this way, more reciprocating parts, inertial mass, is not conducive to high-speed engine movement. Moreover, the elongated tappet has a certain elasticity, easily lead to vibration, accelerated wear parts, and even control the valve out of control.

Top double camshaft is installed in the cylinder head with two camshafts, one for driving the intake valve, the other for driving the exhaust valve. Double overhead camshafts have low design requirements on camshafts and valve springs. They are especially suitable for hemispherical combustion chambers with V-shaped valves. They are also suitable for use with the four-valve valve train.