Marine Diesel Engines

Fairbanks-Morse Company

Model 38D-8-1/8 Opposed Piston Engine

Above: The Fairbanks-Morse Catalog Cover for the Model 38D-8-1/8 Engine



The Fairbanks-Morse Model 38D-8-1/8 is a two stroke cycle opposed piston diesel engine. As the name implies, it is an 8-1/8 inch bore engine that went into production in 1938 using a design based on German technology. Fairbanks-Morse also built a smaller 5-1/4 inch bore opposed piston engine with very similar design and features. The engine featured a welded crankcase and an unusual cylinder liner arrangement with two pistons per cylinder and no cylinder head. The cylinders have no intake or exhaust valves, the air is admitted and the exhaust is expelled through ports in the liner wall, with the opening controlled by the travel of the pistons in the cylinder. There are two fuel injection nozzles per cylinder, directly across from each other on the liner wall, that inject fuel into a firing chamber formed by the heads of the two pistons.

The Fairbanks-Morse OP engine was one of the engines able to pass the mid-1930s U. S. Navy submarine qualification tests, and was approved for application to fleet submarines. The GM-owned Winton Engine Company, which became the Cleveland Diesel Engine Division of GM in 1937, was another builder whose products passed the submarine qualification tests, and they split the business for new construction fleet submarines about equally with FM during the late 1930s and through World War Two.

The Fairbanks Morse OP engine achieved an enviable record for reliability in submarine service, and this made Fairbanks-Morse a strong contender for postwar diesel marine engine sales. They also entered the diesel locomotive market, compenting with Electro-Motive, ALCO, Baldwin, Lima, and later General Electric. Despite the success of the OP engine in submarine service, it was treated rather indifferently under railroad maintenance, and suffered as a result. The FM product tended to be regarded as an oddity on railroads, and this led to a retreat from the US railroad market in 1953 and a complete exit by 1960. Throughout this period, FM continued to build and sell OP engines for marine and industrial use, and the engine remained in widespread use in new construction for the U. S. Navy for many decades. Today the Navy continues to run many OP engines and is the largest remaining marine customer for the Fairbanks-Morse 38D-8-1/8.

Article and page design by Preston Cook, ©2009 by T.E.S.


Above: The 12 cylinder Fairbanks Morse 38D-8-1/8 engine was an extremely powerful prime mover at the time of its introduction, typically rated at 2400 horsepower in the Roots blower version. The same engine with series turbocharging was rated at up to 3600 horsepower.


Above: This diagram shows the unusual arrangement of the pistons and connecting rods in the Fairbanks Morse Opposed Piston diesel engine. Two pistons share the cylinder, one connected to the upper crankshaft and the other to the lower crankshaft. Timing between the two crankshafts is coordinated by a vertical drive with a spring cushion pack.


Above: Fairbanks Morse advertising in the marine trade press took full advantage of the excellent record of their engines in World War Two U. S. Navy Fleet Submarines. This wartime FM ad tells of the missions of the USS Wahoo.


Images courtesy of Fairbanks-Morse Company


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