The Lycoming O-320 is a large family of naturally aspirated, 320 cuin air-cooled, horizontally-opposed four-cylinder, direct-drive engines produced by Lycoming Engines. Introduced in 1953, it is commonly used on light aircraft such as the Cessna 172 and Piper Cherokee, and remains in production as of 2024. Different variants are rated for 150 or 160 horsepower (112 or 119 kilowatts).

Design and development

The O-320 family of engines includes the carbureted O-320, the fuel-injected IO-320, the inverted mount, fuel-injected AIO-320 and the aerobatic, fuel-injected AEIO-320 series. The LIO-320 is a "left-handed" version with the crankshaft rotating in the opposite direction for use on twin-engined aircraft to eliminate the critical engine. The first O-320 (with no suffix) was FAA certified on 28 July 1953 to CAR 13 effective 5 March 1952; this same engine was later re-designated, without change, as the O-320-A1A. The first IO-320 was certified on 10 April 1961, with the AIO-320 following on 23 June 1969 and the first aerobatic AEIO-320 on 12 April 1974. The LIO-320s were both certified on 28 August 1969. The O-320 family of engines externally resembles the Lycoming O-235 and O-290 family from which they were derived. The O-320 shares the same 3.875 in stroke as the smaller engines, but produces more power with the bore increased to 5.125 in. The design uses hydraulic tappets and incorporates the provisions for a hydraulically controlled propeller installation as well. The controllable-pitch propeller models use a different crankshaft from those intended for fixed-pitch propellers. The O-320 uses a conventional wet sump system for lubrication. The main bearings, connecting rods, camshaft bearings, tappets and pushrods are all pressure lubricated, while the piston pins, cylinder walls and gears are all lubricated by spray. The oil system is pressurized by an accessory-drive mounted oil pump. A remotely mounted oil cooler is used, connected to the engine by flexible hoses. The 150 hp versions of the carbureted O-320, are approved for the use of 87 AKI automotive gasoline. Models with 9.0:1 compression ratio are not approved, such as the H2AD model. All other 160 hp 0-320s are approved for 91 AKI. Airframe approval is also necessary to use automotive gasoline in any certified aircraft. The factory retail price of the O-320 varies by model. In 2010 the retail price of an O-320-B1A purchased outright was USD$47,076

Variants

O-320 series

IO-320 series

LIO-320 series

AIO-320 series

AEIO-320 series

Applications

• Aero Eli Serviza Yo-Yo 222 • Aviat Husky A-1B-160 • Avid Flyer • Aero Commander 100 • Alpha 160A • American Champion Citabria • Australian Aircraft Kits Hornet STOL • Australian Lightwing SP-4000 Speed • Aviation Industries of Iran AVA-202 • Beagle Pup Series 2 and 3 • Bearhawk Companion • Beechcraft Musketeer • Bede BD-12 • Bellanca Decathlon • Bushcaddy L-160 • Canadian Home Rotors Safari • Cessna 172 • Cessna 177 • Custom Flight North Star • Christavia Mk IV • Dakota Cub Super 18 • DRDO Rustom • EM-11 Orka • Eaves Cougar 1 • Explorer Ellipse • Falconar F12A Cruiser • Farrington Twinstar • Fly-Fan Shark • Fuji FA-200 Aero Subaru • Glasair GlaStar • Grumman American AA-5 • Gulfstream American GA-7 Cougar • Hatz CB-1 • Hatz Classic • IRI T22B • Lambert Mission 212 • MBB Bo 209 • Mooney M20 • Murphy Elite • Mustang Aeronautics Mustang II • Osprey Osprey 2 • Partenavia P66B Oscar 150 • Peña Dahu • PIK-15 • PIK-19 • Piper PA-20 Pacer • Piper PA-18 Super Cub • Piper PA-23 Aztec • Piper PA-23 Apache • Piper PA-28 Cherokee • Piper PA-30 Twin Comanche • Piper PA-40 Arapaho • Preceptor STOL King • PZL-110 Koliber • Quikkit Glass Goose • Rihn DR-107 One Design • Robin DR400 • Robinson R22 • Rutan Long-EZ • Sands Fokker Dr.1 Triplane • SGP M-222 Flamingo • SME Aero Tiga • Socata TB9 Tampico • Softex-Aero V-24 • Symphony SA-160 • Tapanee Levitation 2 • Thorp T-18 • Van's Aircraft RV-3 • Van's Aircraft RV-4 • Van's Aircraft RV-6 • Van's Aircraft RV-8 • Van's Aircraft RV-9 • Varga Kachina • Velocity V-Twin • Vortech Shadow • Vulcanair P-68C • Wassmer WA 52 • Whisper X350 Generation II • Wickham B • Wittman Tailwind

Specifications (O-320-A1A)