An engine includes a crankshaft, a first noncircular gear operatively connected to the crankshaft to be driven thereby, a second noncircular gear meshingly engaged with the first noncircular gear, a cam operatively connected to the second noncircular gear to be driven thereby, and a valve operatively connected to the cam for movement between open and closed positions. The noncircular gears enable the speed of the cam to vary cyclically with constant rotation of the crankshaft speed. Valve lift timing and duration may be variable by moving the second noncircular gear with respect to the first noncircular gear while maintaining meshing engagement therebetween.