Abstract: This invention deals with an improved rotary engine of the rotating abutment type and, more particularly, with a unique movement control mechanism which is suitable for use with such an engine. An engine of this type is equipped with two of these movement control mechanisms, each of which is arranged to control the operation of two of the engine's four pistons. In particular, each movement control mechanism is operable to periodically prevent rearward movement of its associated pistons for a predetermined interval and to limit forward movement of these pistons to a set distance during said predetermined interval. Each movement control mechanism is also operable to periodically couple its associated pistons to the engine's central shaft to thereby transfer rotary motion to and receive rotary motion from the central shaft at regular and predetermined intervals.