The Lycoming O-145 is a family of small, low-horsepower, four-cylinder, air-cooled engines.

[1][2] All models of the series had the same bore, stroke, and displacement, additional horsepower being generated by increasing compression ratio and maximum rpm.

[1][2] The original O-145-A produced 55 hp (41 kW) at 2300 rpm, weighed 165.5 lb (75 kg), and featured single ignition.

The O-145 had a hard time competing with the same horsepower Continentals due to its smaller displacement, which resulted in a steeper torque curve.

The GO-145 suffered from a poor reputation for reliability, because pilots mis-handled the engine, running it at too low a cruising rpm and causing gearbox wear as a result.