The rocker arm shaft transforms the circular motion of the camshaft into a linear movement that opens and closes the intake and exhaust valves at the precise moment during engine combustion. They also help reduce friction between the camshaft and the valves, thus promoting smoother and longer-lasting engine operation. Make sure the engine is well lubricated, change the oil and filter as directed, and check the valves properly to prevent wear. A rocker arm shaft in good condition is the secret to a strong, smooth engine.