What Is a Hydraulic Tappet?
A hydraulic tappet is a device used to open and close valves in an internal combustion engine. Riding on the camshaft lobe, the hydraulic tappet, or lifter as it is commonly called, actuates the valve via a push rod and rocker arm. The function of the hydraulic tappet is to maintain zero lash, or gap, between the tip of the rocker arm and the tip of the valve stem. Adjusted with a slight preload, the hydraulic tappet uses engine oil to maintain the zero lash setting while the engine is running.
