Abstract: An improved two-cycle internal combustion engine with a novel intake, exhaust and piston arrangement in which a fresh charge for combustion is advantageously transferred through the piston and all valves in the engine operate in response to changes in dynamic pressure generated within the engine. The piston includes at least one charging passage through its top surface with a pressure sensitive valve affixed to the top surface of the piston for preventing flow of a fresh charge through the charging passage in the absence of a greater pressure differential caused by the intake charge against the undersurface of the pressure sensitive valve.