Tappet

A tappet is the noise made by a worn cam follower, however the term is widely used to represent the cam follower itself. In mechanical engineering it is a projection which imparts a linear motion to some other component within an assembly. Properly speaking, a tappet is the only part of a rocker arm that makes contact with an intake or exhaust valve stem above the cylinder head of an internal combustion engine. As the cam rotates, it creates both a sideways and a downward force on the tappet. Without a tappet (and with the cam acting directly on the valve), the sideways force would cause the valve stem to bend. With a tappet, the sideways force is transferred to the cylinder head so only the downward force acts on the valve stem.