Franklin, with Continental and Lycoming, was one of the "big three" of horizontally-opposed engines in the late 1930s and early 1940s. Franklin became an "also ran" after World War II.
1893: H.H. Franklin Manufacturing is formed.
1902: The first Franklin automobile is sold. It has a four cylinder air-cooled engine.
1934: The Depression bankrupts Franklin
1937: A group of Franklin engineers buy the assets of H.H. Franklin Co. and form Air Cooled Motors Development Co. Engines are marketed under the Franklin name.
1945: Air Cooled Motors is acquired by Republic Aircraft to produce engines for its RC-3 Seabee.
1948: Tucker Industries buys Air Cooled Motors from Republic to develop a liquid-cooled engine for the 1948 Tucker.
1961: Tucker sells Air Cooled Motors to Aero Industries which renames the company Franklin Engine Co.
1975: Rights to Franklin engines are bought by the Polish government which begins production of PZL-Franklin engines in Rzeszow.
In 1941, Franklin introduced four new engines based on a 4.25 x 3.5 inch cylinder. These engines were the 4-cylinder 4AC-199, the 6-cylinder 6AC-298, the 8-cylinder 8AC-398 and the 12-cylinder 12AC-596.
The U.S. military gave the 6AC-298 the designation O-300. Production ended in 1945. A later Continental engine received the same designation.
6-cylinder, horizontally-opposed, air-cooled piston engine
Displacement: 298 cubic inches (4.9 litres)
Bore x stroke: 4.25 x 3.5 inches