Four-cycle internal-combustion engines in which the combustible charge enters the working cylinder and after ignition and expansion the burned gases are exhausted therefrom through a single passage controlled by a single positively-operated poppet or equivalent valve, said common passage being provided with means for directing the flow of the combustible charge from a supply-conduit to the common conduit and for directing the flow of the exhaust-gases from such common conduit into the exhaust-conduit leading from the engine. The directing means ordinarily comprise a valve or valves operated either positively or by the suction and pressure alternately existing in the common conduit, and such means are protected from the pressure of the gases within the cylinder by the single valve.
