Valve guides are precision-machined tubular components installed within cylinder heads, providing a low-friction surface for valve stem travel. They maintain valve alignment, controlling valve motion and ensuring proper sealing against valve seats. Typically manufactured from cast iron, bronze, or steel alloys, guides feature internal diameters precisely sized for specific valve stems. Some designs incorporate hardening treatments for increased wear resistance, and external features for oil retention. Proper guide clearance is critical for optimal engine performance and preventing oil consumption.