Abstract: A rotary cylinder fluid pressure machine such as an internal combustion engine (10) has a cylindrical stator (11) within which there is rotatable a rotor (12) from which project five cylinders (13, 14, 15, 16, 17). The cylinders (13, 14, 15, 16, 17) are equi-angularly spaced about the rotational axis of the rotor (12) and are equally spaced along the said axis. In each cylinder (13, 14, 15, 16, 17) is a respective piston (18, 19, 20, 21) connected by a respective connecting rod (23, 24, 25, 26 27) to respective crank pins of a crank shaft (33) which is coaxial with the rotor (12). The five throws of the crank shaft (33) bearing the respective crank pins have the same equi-angular separation as the cylinders (13, 14, 15, 16, 17). The rotor (12) and crank shaft (33) are interconnected by bevel gears (not shown) whereby rotation of one will cause counter-rotation of the other at the same speed.