Automatic compression relief mechanism for internal combustion engines

In an internal combustion engine, a latch member is movable to and from a latching position in which it prevents a valve from coming nearer its seat than a predetermined distance therefrom. A cam follower connected with the latch member cooperates with axially adjacent first and second cam elements. The first causes the latch member to be held out of latching position during most of the engine cycle at all speeds, but at cranking speeds causes it to move to latching position just before the valve, in closing, reaches said distance from its seat. Once in latching position, the latch member is trapped there until opening movement of the valve carries it beyond said distance from its seat. The second cam element, carried by a flyweight, so cooperates with the first at running speeds as to hold the latch member out of latching position throughout the cycle.