Valvetrain

A valvetrain is a mechanical system that controls the operation of the intake and exhaust valves in an internal combustion engine.

The timing and lift profile of the valve opening events are controlled by the camshafts, through use of a carefully shaped lobe on a rotating shaft.

Depending on the design used, the valves are actuated by a rocker arm, finger, or bucket tappet.

Overhead valve engines use rocker arms, which are actuated from below indirectly (through the pushrods) by the cam lobes.

Overhead camshaft engines use fingers or bucket tappets, which are actuated from above directly by the cam lobes.