Tappet (valve lifter)

A tappet, also called a cam follower or valve lifter, sits between the camshaft lobe and the valve or pushrod. It turns the rotating cam into the up-and-down motion that opens the valve.

Types you will meet:

• bucket tappets in many overhead-cam engines, with a thin shim on top or underneath to set the clearance;
• screw-and-locknut adjusters on rocker arms, common on older and simpler engines;
• hydraulic tappets, which take up the clearance automatically with oil pressure, used on some cruisers such as Harley-Davidson twins.

Mechanical tappets need periodic valve clearance checks. A light ticking is often normal, but louder clatter can mean excessive clearance or low oil pressure.