Abstract: Valve control apparatus adapted for use in a rotary engine or pump having a cylinder block rotatable about an axis and including a plurality of cylinders and corresponding pistons radially arranged about the axis, a plurality of valves each disposed in a different one of the cylinders, and a plurality of tappet mechanisms each of which when actuated operates to alternately open and close a different one of the valves. The valve control apparatus includes a cam ring having first and second generally circular cam tracks defined therein for contacting and actuating certain ones of the tappet mechanisms. The cam tracks are disposed in substantially parallel planes and each includes a pair of lobes positioned diametrically opposite in the cam ring. The cam ring is adapted to rotate about the axis in the same direction as the cylinder block but at a speed different therefrom to provide for coaction between the cam tracks and the various tappet mechanisms.