Both powerplants share the same crankcase, although the C-145 produces an additional 20 hp (15 kW) through a longer piston stroke, higher compression ratio of 7.0:1 and different carburetor jetting.

[1] The O-300 is a modernized C-145 and retains the same weight, dimensions, bore, stroke, compression ratio, displacement and output power of the earlier engine.

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.

[2] Reference: Engines for Homebuilt Aircraft & Ultralights[1]