Abstract: A multi-cylinder gas engine featuring a unique method of gas fuel intake and cylinder exhaust gas scavenging and recharging. It is a three cylinder opposed piston two-stroke cycle engine combined with a three cylinder opposed piston, sequentially ported, valveless pump to produce a three-stroke cycle engine effect. The engine has a positive compression, power, and recharge strokes, but no actual exhaust stroke. Exhaust is accomplished by pressure "blowdown" and by displacement scavenging of the cylinders during the recharge stroke. Operation may be based on the Otto cycle (gasoline or fuel, glow plug or spark ignition) or the diesel cycle and may utilize one or more carburetors or fuel injection. The firing order is sequential, in the same direction as crankshaft rotation, equally spaced (120 degrees), and results in three power strokes of approximately 120 degrees duration per revolution. A pump is also described.