rocker arm. Main Parts of Cylinder Head In a piston engine, the cylinder head sits above the cylinders, forming the roof of the combustion chamber. In side valve engines the head is a simple plate of metal containing the spark plugs and possibly heat dissipation fins. In more modern overhead valve and overhead camshaft engines, the head is a more complicated metal block containing the inlet and exhaust passages, and often coolant passages, Valvetrain components, and fuel injectors. 1. Valve Spring: An engine valve spring is a coil spring that keeps the valves in an internal combustion engine in the correct position and opens and closes them properly. 2. Camshaft: A camshaft is a shaft containing a row of pointed cams to convert rotational motion to reciprocating motion. 3. Rocker Arm: A rocker's arm is a lever in an internal combustion engine that transfers motion from the camshaft to open the intake or exhaust valves. 4. Rocker Shaft: A rocker shaft in an engine is a component ...