1981 and later the return spring holds it in , if the crankcase has chain damage around the seal lip u may have to make up something like a piece of alum bent to go over the top of the arm and fix it to the sproket cover bolt , also if the part of the actuator that contacts the pushrod is bent the wrong way it can act as a wedge and try to push the thing up when it takes the load , pre 81 has a steped screw that engages in a slot in the act. shaft