The rocker lever group consists of the rocker lever assembly, the step timing control (STC) oil manifold connector, external oil manifold, internal oil tube, and the rocker housing cover. The rocker levers contain replaceable bushings. The intake, exhaust, and injector rocker levers contain ball plugs to plug the oil drilling holes in the levers. The rocker lever pad on the intake and exhaust rocker levers is precision ground and must not be repaired. Oil flows through the rocker lever shaft to the rocker levers. The levers are push rod actuated and use an adjusting screw to control the clearance between the lever and valve crosshead or injector link.