Valvetrain

The valvetrain is the mechanism that lets the fresh mixture into the cylinder and the exhaust gases out at exactly the right moments. It includes the camshaft or camshafts, the cam drive (chain, belt or gears), tappets or rocker arms, valve springs, and the valves themselves.

Common layouts on motorcycles are SOHC (one overhead camshaft), DOHC (two overhead camshafts, usually four valves per cylinder) and OHV pushrod engines with the camshaft in the block, used by many cruisers. Ducati's desmodromic system closes the valves mechanically instead of with springs.

Key maintenance points are valve clearance checks, cam chain tensioner condition and, on belt-driven engines, timing belt replacement at the specified interval.