Abstract: The rotary valve engine of the present invention comprises an engine block containing four power cylinders and a central valve cylinder. A single valve port is located in each cylinder just above the maximum travel of the piston. This port serves alternately as an intake port and as an exhaust port. A valve spool is rotatably mounted in the valve cylinder and includes a fuel-air channel in communication with a source of fuel-air mixture and an exhaust port in communication with the atmosphere. The valve spool is rotatable to cause the fuel-air channel and the exhaust channel to move into sequential communication with the valve port of each power cylinder so as to provide charging and exhausting of the power cylinders in proper succession. Two crank shafts are provided, and are linked together by external gears to cause synchronous counter-rotation in such a manner that intake compression, power and exhaust strokes are coordinated and the inertial forces of the engine are counter balanced at all times.