The 2.8L diesel features a free-wheeling driven sprocket on the intake camshaft, which is tightened once the relationship between the camshafts and the crankshaft has been established. The crankshaft sprocket must be held in a timed position in relation to the camshafts to service the timing belt drive system, the water pump, or the high-pressure fuel pump. Due to the hydraulic engine mounts in the GMNA 31XX trucks, there is no access to the crankshaft locking plug on the side of the block, and the previous crankshaft locking tool, GM-50030, cannot be used. GM-51265 mounts to the crankshaft sprocket, locking it into position with the block. After GM-51265 is installed, the camshafts can be locked into position, and the timing belt, water pump, or fuel pump can be serviced. If GM-51265 is not used, the engine must be manually re-timed, or engine damage may occur.