A valvetrain or valve train is a mechanical system that controls the operation of the intake and exhaust valves in an internal combustion engine. Wikipedia

Mechanical system that controls operation of the valves in an internal combustion engine Wikidata

A valve (as in an internal combustion engine) which consists of a sliding shaft with a disk on the end (the disk being shaped to alternately plug and unplug a matching port) and which is operated by springs and possibly cams interacting with the shaft. Wiktionary