An overhead camshaft (OHC) engine is a piston engine in which the camshaft is located in the cylinder head above the combustion chamber. This contrasts with earlier overhead valve engines (OHV), where the camshaft is located below the combustion chamber in the engine block.
OHC cylinder head (for a 1987 Honda D15A3 engine)
SOHC design (for a 1973 Triumph Dolomite Sprint)
DOHC design (for a V12 engine)
Rubber timing belt during installation
In a piston engine, the cylinder head sits above the cylinders, forming the roof of the combustion chamber. In sidevalve engines the head is a simple plate of metal containing the spark plugs and possibly heat dissaption fins. In more modern overhead valve and overhead camshaft engines, the head is a more complicated metal block that also contains the inlet and exhaust passages, and often coolant passages, Valvetrain components, and fuel injectors.
Side view of a DOHC cylinder head (with the valves and camshafts installed)
Underside of a OHV cylinder head (with the valves installed)
DOHC head- cutaway view
SOHC Honda D15A3 engine