Free valve compression relief for four cycle engines

Claim 1

In a four-stroke cycle internal combustion engine having a camshaft rotatably driven in timed relation to the engine cycle, a poppet valve having a stem and a head engageable with a seat, and means for actuating the valve in timed relation to the engine cycle comprising a cam on the camshaft that moves the valve away from its seat, a spring which urges the valve towards its seat and which reacts between a fixed part on the engine and a spring retainer connected with the stem of the valve, and a tappet member coaxial with said stem and interposed between the valve and the cam: A. cooperating means on the stem of said valve and on its spring retainer providing a lost motion connection between them which allows the valve to have limited motion relative to the spring retainer; B. an auxiliary tappet member confined between the camshaft and the spring retainer, said auxiliary tappet member 1. being guided for motion parallel to and adjacent to the tappet member, 2. having an enlarged foot portion at its end adjacent the camshaft, and 3. having a circumferential shoulder at its other end which engages the spring retainer around the valve stem; and C. a cam element on the camshaft, axially adjacent to the cam and rotatable therewith, said cam element being cooperable with the foot portion of the auxiliary tappet member to so position the spring retainer, during a predetermined portion of the engine cycle in which the cam allows the valve to be closed, as to leave the valve substantially free for limited motion to and from engagement with its seat so that the valve can respond to differences between pressures inside and outside the cylinder and can therefore open slightly to relieve such pressure differences during starting of the engine.