What is "valvetrain"

n. The collective mechanisms and parts that control the operation of the valves in an internal combustion engine.

A valve train or valvetrain is a mechanical system that controls operation of the valves in an internal combustion engine, in which a sequence of components transmits motion throughout the assembly. A traditional reciprocating internal combustion engine uses valves to control air and fuel flow into and out of the cylinders, facilitating combustion.