The Lycoming O-235 is a four-cylinder, horizontally opposed aircraft piston engine with air cooling and a direct propeller drive. Its 233.3-cubic-inch displacement places it among Lycoming's smaller conventional aircraft engines. The family includes several compression ratios and power ratings, and an O-235-N2C installation powers the Cessna 152.[1][2]
Mechanical arrangement
The cylinders combine aluminium-alloy heads with steel barrels carrying cooling fins. A camshaft above the crankshaft operates the valves through solid tappets and rockers. Valve clearance is set mechanically with adjusting screws, a distinguishing feature of the O-235 described in Lycoming's manual. The crankcase consists of two aluminium-alloy halves, while the crankshaft is a steel forging.[1]
Fuel, cooling and lubrication
A float carburettor supplies the intake pipes through passages associated with the oil sump. Two magnetos provide dual ignition. Engine cooling depends on baffles directing air through the cylinder fins, while an accessory-housing pump circulates oil through a pressure-fed wet-sump system. These separate systems combine air cooling of the cylinders with oil circulation for lubrication.[1]
Ratings and the Cessna installation
The O-235-C and E series are rated at 115 hp at 2,800 rpm, while the K, L and M series have a 118 hp rating. The N and P engines use an 8.1:1 compression ratio and a 116 hp rating.[1]
Lycoming's Cessna 152 replacement listing identifies the N2C with a dynafocal mount, 24-volt electrical installation and two 4381 magnetos. The listed configuration includes a Sky-Tec starter and an oil filter, but no engine fuel pump or pump drive. These details show how an engine model becomes a specific aircraft installation through its mounting, starting equipment and accessories.[2]