Variable valve timing mechanism for engine

Several embodiments of variable valve timing mechanisms for an internal combustion engine wherein the timing of two valves associated with the same combustion chamber of the engine may be driven at the same time interval and at the same speed from the engine output shaft and both valves may have their timing adjusted simultaneously by a first variable valve timing mechanism and only one of the valves may have its timing adjusted relative to the other valve by a second variable valve timing mechanism to provide a simpler operational control and lower cost assembly.