Abstract: An internal combustion engine includes(a) a pair of opposed cylinders and pistons reciprocating therein,(b) power and return rollers carried by each of the pistons to reciprocate therewith during piston travel,(c) a power output shaft having an integral and external driven cam located to be driven in rotation by the power rollers in response to power stroke travel of the pistons, the shaft having an axis of rotation,(d) a flange integral with the output shaft and having an internal cam track located to be engaged by the return rollers in response to return stroke travel of the pistons,(e) said power and return rollers having parallel axes of rotation, the return roller axes located closer to the shaft axis than the power roller axes.