Abstract: A pair of cylindrical rotors are mounted for rotation within a stator and each rotor including a plurality of cylindrical bores annularly around the axis thereof and parallel to the stator bore. Pistons reciprocate within these bores and connecting rods or links of the pistons engage within the profile of a pair of annular cams secured to the stator at opposite ends thereof so that as the rotors rotate, the pistons reciprocate due to the cam profile. By providing a set of pistons and cylinders, on each side of a central common cylinder head at each end, a pair of rotors and a pair of cams one at each end of the stator, balance is achieved. A common combustion chamber is provided in the cylinder head for the pistons on the opposite sides of the cylinder head. The cycle can be of a diesel type with a fuel injection or of the gasoline/air mixture type with conventional spark plugs.