Abstract: A rotary engine having a toroidal chamber which is stationary, and in which the pistons convey power to a common crankshaft under the control of a four-bar linkage including novel means for preventing reverse motion of any piston in the chamber. Inlet and exhaust valves to control the flow of energizing fluid are provided, and are actuated directly from the crankshaft. Novel sub-components include the four-bar linkage, the valving mechanism, and the arrangement by which rotary movement of the pistons in the chamber is eliminated.