What is Tappet Clearance ?

A tappet is a projection (act, process) which communicates a linear motion to some other component within a mechanism. The tappet is that part, also termed a cam follower.

In an overhead valve engine, this tappet is fitted low down in the engine block. From there it drives a long thin pushrod, up to the top of the engine. Here the rockers arms press the valves downwards to open them.

 

Tappet Clearance  adjusts the overall clearance in the valve actuation system. The name arises because it is the clearance of the tappets that is being adjusted, even though the adjustment is not made to the tappets themselves.