a screw jack , for raising the power piston of a diesel engine &# 39 ; s control governor until the power piston firmly clamps the gap gage , is provided to maintain the piston in its full load position during the adjustment of the engine fuel pump racks to match the governor piston gage , this adjustment being done when the diesel engine is shut down and the start contactors blocked open or insulated . the screw jack contains a break joint which , in its fully operative clamping position , can be rendered instantly inoperative simply by breaking the joint of the jack manually , a result effected by a single karate - like sweep of the hand .