rockerarm

A rocker arm is a lever in an internal combustion engine’s valve train that transmits motion from the camshaft to the intake or exhaust valve, converting the cam’s rotation into upward valve movement. It sits on a fulcrum and uses one end to receive motion from a lifter or cam follower (via a pushrod in pushrod/ohv designs) and the opposite end to press on the valve stem to open the valve.

In different engine layouts, rocker arms can operate in various ways. In overhead valve engines, the pushrod and lifter push on the rocker arm, which pivots to open the valve. In overhead cam designs, the cam lobe may actuate the rocker directly or via a follower or bucket tappet, with the rocker then driving the valve. The valve lift produced by a rocker arm depends on its lever ratio, with higher ratios increasing lift but potentially changing valve timing and spring requirements.

Rocker arms are typically made from steel or aluminum, and may be forged or cast with machined contact surfaces. Some designs include adjustable rockers that allow setting valve lash, while many modern engines use hydraulic lifters or built-in lash compensation to eliminate manual adjustment.

Maintenance considerations include ensuring proper lubrication, correct mounting torque, and wear inspection of the pivot, contact surfaces, and valve-end interface. Common issues include wear-induced play, bending, or misadjustment, which can lead to valve train noise, reduced performance, or valve timing irregularities.

Rocker arms are part of the broader valve train, which also includes the camshaft, lifters, pushrods, and valves, all contributing to the engine’s intake and exhaust cycle.