The Lycoming O-540 is a family of carburetted, six-cylinder aircraft engines with a horizontally opposed layout, air cooling and direct propeller drive. Its applications range from larger light singles to utility transports. Examples include the Piper Cherokee 235, Comanche, Cherokee Six and piston-powered Britten-Norman Islander.[1][2]
Construction and drive
The O-540-A4E5 illustrates the family's mechanical arrangement. Its crankcase is divided into two reinforced castings, and the propeller shaft forms part of the crankshaft. Counterweights reduce torsional vibration. A camshaft above the crankshaft works hydraulic roller tappets, pushrods and rockers to operate the valves. Oil can pass through the propeller shaft to operate a controllable-pitch propeller.[1]
Engine systems
The A4E5 has a diaphragm fuel pump and a carburettor with mixture control. Two magnetos serve twelve spark plugs, providing two plugs per cylinder. Cooling baffles direct air between the cylinder fins. The wet-sump lubrication circuit includes an external cooler and a bypass path for conditions that restrict oil flow through the cooler.[1]
Applications and equipment
Lycoming lists the O-540-B4B5 at 235 hp for the PA-28-235 Cherokee. A listed replacement configuration includes a dynafocal mount, 12-volt electrical equipment, two impulse magnetos, an oil filter and a front-left propeller-governor position. Engine accessories therefore reflect the requirements of the particular airframe.[3]
The manufacturer's installation catalogue associates O-540-A variants with the 250 hp Comanche and Aztec, and the E4A5 with the Comanche 260 and SIAI-Marchetti SF.260. The E4B5 appears in the Cherokee Six and BN-2, while the E4C5 serves Islander and Trislander versions. These installations place the carburetted O-540 in touring, training and transport roles; the related fuel-injected IO-540 carries a separate designation.[2]