Rotary engine and pump

In an engine, a pair of spaced working chambers defined by a cylindrical wall having an inner surface, a piston movable linearly in said working chamber in response to gas pressure in said chambers and in gas sealed relation with said cylindrical wall, said piston having end walls with cylindrical apertures, an output shaft having cylindrical shaft portions extending through said apertures, and guide means on said piston and cylindrical wall to cause guided rotary movement of said piston upon axial movement of said piston, and means on said output shaft between said piston end walls for drivingly and slidingly connecting said output shaft to said piston to impart rotary motion to said shaft upon rotation of said piston and wherein said guide means comprises an oval groove recessed in said inner surface of said cylinder and inwardly open towards said piston, said groove being in an transverse plane with respect to the axis of travel of said piston and said groove limiting travel of said piston between two opposed piston positions and two guide rollers located in said groove and supported for free rotation on said piston about an axis radial with respect to said piston, said rollers having different diameters and said groove being defined by a groove bottom wall and first, second and third grove side walls, said first and second side walls being opposite said third side wall and wherein said first side wall joins said bottom wall and is spaced from said third wall a distance less than the distance of said second wall from said third wall, to form a stepped shoulder within said groove and wherein said smaller diameter roller rollably engages said first side wall and said larger diameter roller rollably engages said third wall.