Rocker Arm
A pivoting lever that transfers the upward motion of a pushrod or camshaft lobe into the downward motion that opens the intake or exhaust valve.
A rocker arm is a pivoting lever in the engine's valvetrain that acts as a mechanical bridge between the camshaft and the valves. In pushrod (overhead valve, or OHV) engines, the rocker arm pivots in the center: when the camshaft pushes up on the pushrod at one end, the rocker arm pivots and pushes down on the valve stem at the other end to open the valve.
In overhead camshaft (OHC) engines, rocker arms are often called follower arms or finger followers, pivoting at one end while resting on the camshaft in the middle and the valve at the other. Rocker arms can have different ratios (e.g., 1.5:1), meaning they multiply the lift of the camshaft lobe to open the valve further, allowing more air and exhaust to flow through the engine.
Rocker arms are subject to high sliding friction and load. Modern rocker arms often feature a roller tip containing ball bearings that rolls over the valve stem and camshaft to reduce friction and wear. Symptoms of rocker arm problems include ticking or clacking noises, engine misfires, and reduced performance if a rocker arm pivots off its mount or wears excessively. Replacing a worn rocker arm involves removing the valve cover and loosening the rocker shaft or pivot bolts.