Auto-decompression system for engines

Abstract

A valve control device including a decompression cam. The decompression cam fits loosely on the camshaft adjacent to a valve motion cam. The decompression cam may be selectively moved and retained so as to extend beyond the valve motion cam to control the associated cam follower during the compression stroke. An eccentric weight is associated with the decompression cam so as to draw it from an extension beyond the valve motion cam under normal operating conditions. When starting, a spring biases the decompression cam outwardly so as to interlock the cam with a projection associated with the camshaft. When the projection retains the decompression cam outwardly against the cam follower, an associated engine valve is partially open to reduce compression during the compression stroke. Further rotation releases the decompression cam from the projection and allows the centrifugal force operating on the eccentric weight to draw the decompression cam out of operation for normal running. A reverse, decompression cam operates by means of a one-way clutch to lift the associated cam follower when the engine rotates partially in reverse. When rotating normally, the reverse, decompression cam is declutched from the camshaft and remains inoperative.