Abstract: A single piston internal combustion engine is described that produces two power impulses per revolution of the crankshaft, precise mechanical balance, zero side thrust upon the piston, and purified exhaust gas. The lubrication oil is isolated from contamination by blowby and fuel dilution. Total engine cooling is obtained from the lubrication oil. The engine is free from shock loads as it is cushioned by continuously compressing gas in preparation for the next combustion event. The engine is uniflow-scavenged utilizing piston pumps whose fresh air intake is controlled by rotary valves. The piston pumps possess compact aftercoolers used in combination with supercharging. The exhaust header assists in silencing the engine and removes fluctuations in exhaust pressure. A computer-aided specialized mechanical balance methodology is disclosed that obtains counterbalance weights to optimally reduce engine shaking forces.