The Lycoming O-320 is a carburetted, air-cooled four-cylinder aircraft engine with a horizontally opposed layout. Its crankshaft drives the propeller directly, and displacement is 319.8 cubic inches. Versions rated at 150 and 160 hp powered a broad range of light aircraft, including Cessna Skyhawks, Piper Warriors and the early Robinson R22 helicopter.[1]O-320 Operator's ManualLycoming · lycoming.com · Accessed 2026-09-13Open source details[2]320 Series engine installationsLycoming · lycoming.com · Accessed 2026-09-13Open source details
Construction
An aluminium-alloy crankcase supports a forged-steel crankshaft. Each cylinder has a steel barrel and aluminium head, with fins exposed to cooling air directed by the aircraft's baffles. The camshaft lies above the crankshaft and operates hydraulic tappets, pushrods and rocker arms. Pressure oil also reaches the valve mechanism through hollow pushrods before returning to the sump.[1]O-320 Operator's ManualLycoming · lycoming.com · Accessed 2026-09-13Open source details
Power and induction
The A and E series have a nominal 150 hp rating at 2,700 rpm and a 7.0:1 compression ratio. The B and D series produce 160 hp at the same speed with an 8.5:1 ratio. A float carburettor supplies a central induction passage and individual cylinder intake pipes. The engine uses dual magneto ignition and wet-sump lubrication.[1]O-320 Operator's ManualLycoming · lycoming.com · Accessed 2026-09-13Open source details
Aircraft installations
The O-320-E3D supplies 150 hp in the Piper PA-28-151 Warrior. Lycoming lists that installation with a dynafocal mount, a low-pressure diaphragm fuel pump, two magnetos and a 12-volt starter. This equipment supports the aircraft's particular fuel and electrical arrangements.[3]O-320-E3D engine detailsLycoming · lycoming.com · Accessed 2026-09-13Open source details
Other applications include the 150 hp O-320-A2B in the PA-18-150 Super Cub and the 160 hp O-320-D3G in the PA-28-161 Warrior II. Cessna installations include the 150 hp E2D and 160 hp D2J. The O-320-B2C appears in the R22B, demonstrating the family's use in rotary-wing as well as fixed-wing aircraft.[2]320 Series engine installationsLycoming · lycoming.com · Accessed 2026-09-13Open source details