DOHC (Double Overhead Camshaft)

DOHC stands for double (or dual) overhead camshaft. Two camshafts sit in the cylinder head: one operates the intake valves and the other the exhaust valves. They are driven from the crankshaft by a chain, belt or gears.

With the cams directly above the valves, there are few moving parts in between, so the valvetrain stays accurate at high revs. DOHC also makes it easy to use four valves per cylinder, which is why most sport bikes and modern motocross and enduro four-strokes use it. SOHC (single overhead cam) and pushrod OHV engines are simpler and more compact.

“DOHV” is sometimes used loosely for the same thing, but it is not a standard engineering term. Valve clearance checks on DOHC engines often require removing the camshafts to change shims.