An internal combustion engine which includes a combustion head adapted to be bolted to the top of a cylinder block and includes a solid cylindrical rotary valve extending longitudinally in a complementary bore in the head which is parallel to the axis of the crankshaft of the engine. The valve has a pair of cutout passages respectively in different rotary angular positions relative to each cylinder in the engine and respectively comprising intake and exhaust passages that communicate respectively with gas inlet ports and exhaust outlet ports in the combustion head, thereby providing a simple substitute for poppet-type valves and the operating mechanism therefor in internal combustion gasoline engines.