The Continental O-300 and the C145 are a family of air-cooled flat-6 aircraft piston engines built by Teledyne Continental Motors. First produced in 1947, versions were still in production as of 2004. It was produced under licence in the United Kingdom by Rolls-Royce in the 1960s.
The C-145 was developed from the 125 hp (93 kW) C125 engine. Both powerplants share the same crankcase, although the C145 produces an additional 20 hp (15 kW) through a longer piston stroke, higher compression ratio of 7.0:1 and different carburetor jetting.
The O-300 is a modernized C145 and retains the same weight, dimensions, bore, stroke, compression ratio, displacement and output power of the earlier engine.
The GO-300 employs a reduction gearbox, so that the engine turns at 3200 rpm to produce a propeller rpm of 2400. The GO-300 produces 175 hp (130 kW) whereas the ungeared O-300 produces 145 hp (108 kW).
The GO-300 engine has a TBO (Time Between Overhaul) of only 1200 hours, while 1800 hours is the standard for ungeared O-300 engines. The GO-300 engine also suffered reliability problems as a result of pilots mishandling the engine and operating it at too low an engine rpm. This caused the Cessna Skylark to develop a poor reputation for engine reliability. Many Skylarks flying today have been converted to different larger displacement direct drive engines.