Valvetrain

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.

Layout

The valve train consists of valves, rocker arms, pushrods, lifters, and camshaft(s). Valve train opening/closing and duration, as well as the geometry of the valve train, controls the amount of air and fuel entering the combustion chamber at any given point in time. Timing for open/close/duration is controlled by the camshaft that is synchronized to the crankshaft by a chain, belt, or gear.

Valve trains are built in several configurations, each of which varies slightly in layout but still performs the task of opening and closing the valves at the time necessary for proper operation of the engine. These layouts are differentiated by the location of the camshaft within the engine: