Fairbanks-Morse 36A Engines

Fairbanks-Morse was a well-established engine manufacturer when they started the development of their first four-stroke, high-speed diesel in 1932. The term “high-speed” is relative, as the new design was rated at what today would be considered a yawn-inspiring 1200 rpm. When compared to Fairbanks Morse’s (F-M) other recently developed two-stroke diesels, which ran at 300 rpm or less, and the rest of the industry at the time, it was indeed a fast-spinning diesel powerplant. F-M had only recently made the change from low compression hot-bulb oil engines to full diesels, but they jumped into the game with both large and small engines.

This 36A is a two-cylinder built in 1936 and makes 20 horsepower at 1200 rpm from 170.2 cubic-inches. The Doherty family named this one “Clyde,” and a second 20 horse in the collection is “Bonny.” This engine was originally hooked up to a water pump. It is hand cranked for starting and has a compression release, the same as many other engines of the era. According to the available period literature, direct electric starting was an available option for the multi-cylinder engines. This engine has a history with the Doherty family. It was a birthday gift to Ken’s wife Marcella in the early days of the new family hobby so she would have a stake in it, and it’s still hers. The engine was just a few days from being bulldozed into a landfill when it was rescued in May of 1972. It’s been to every Tri-State event since then.

The new diesel would emerge for 1934 as the Model 36A, with a 4.25 x 6.00-inch bore and stroke and rated for 10 horsepower per 85.12 cubic-inch cylinder. It was offered in one, two, three, four and six-cylinder inline configurations. A short time later, an inline eight-cylinder was added to the lineup. They were of the “en-bloc” design, meaning the blocks were cast in one piece. Each cylinder head was individual, however, and the engine used wet sleeved cylinders.

The straight-eight version of the 36A was the biggest of the 4.125 x 6 inch bore and stroke units. At 681 cubic inches, it cranked out 80 horsepower at 1200 rpm. That number probably underwhelms you considering the displacement, but at that same rpm, it’s making 350 lbs-ft. and it peaks at approximately 450 lbs-ft. at about 800 rpm by our rough calculation. This one is a marine version pictured in FM literature from 1943. Straight-eight diesels were not uncommon in the ‘30s and ‘40s, particularly in marine applications.

As the 36A design was being finalized for production, work began on a larger displacement version and it debuted in 1935 with a 5.5 x 7.5-inch bore and stroke and a 15 horsepower per cylinder rating at 900 rpm. The rpm rating was later upgraded to 1,200 and the power rose to 20 horsepower per cylinder. The larger version was offered only in four, six- and eight-cylinder inline arrangements and could be converted to run on natural gas. Both the larger and smaller engines carried the 36A designation, but each was delineated by its bore size, e.g. “36A41/4” or “36A51/2.”

The three-cylinder 36A was rated at… you guessed it… 30 horsepower from 255.4 cubic inches. It’s another crank-started engine from the mid 1930s. Details of its working life are not known, but that monstrous nine-sheave pulley hints at something interesting like a compressor.

The 36A engines found widespread use as stationary powerplants, generators, rail locomotive powerplants and for marine propulsion through the ‘30s and ‘40s. A similar en-bloc four-stroke engine debuted for 1938, the Model 46 with an 8 x 10.5-inch bore and stroke, but it only lasted until 1943.  We have been unable to determine exactly when production of the 36A ended but it was probably in the late 1940s.


“The term “high-speed” is relative, as the new design was rated at what today would be considered a yawn-inspiring 1200 rpm.”

In 1939, the 36A was joined by the smaller Model 45 line, which came in several varieties, with either 3.125 x 4-inch or 4.125 x 4.5-inch bore and strokes. The Model 45 came in several evolutions, one with a Lanova style combustion chamber and was mainly seen in one or two-cylinder configurations and was continued into the 1960s. Another F-M four-stroke of the era was the Model 48A, which came in a couple of bore and stroke combos. Though F-M was primarily known for its big two-strokes, they maintained a line of smaller four-strokes into the 1960s.


The 36A series used Bosch APF unit injection pumps driven by roller actuators from eccentrics on the camshaft. The Bosch pumps were controlled via an external rack, which you can see behind the unit. Via the governor, the rack controlled the amount of plunger lift and the amount of fuel delivered to the injector. A separate control (“run” vs “start” in the control picture) retarded injection timing for easier starting. The injectors were also Bosch. You can also see the individual cylinder heads on the engine, which had a cast-in pre-combustion chamber. Injection pressure was listed at around 3,500 pounds.

The engines shown are part of the Ken Doherty memorial collection. Ken began collecting F-M 36As in 1972 and the collection now has four, plus some of the other later F-M four-strokes. All are still in the hands of the Doherty and Hirschy families since Ken passed away in 2016. Grandson Nathan Hirschy has become the keeper of the F-M flame. These engines are brought regularly to the annual Tristate Engine and Tractor Show and can be seen there chugging away demonstrating the thrilling days of yesteryear.

Here’s a 1938 one-cylinder 36A power unit rated at 10 horsepower from 85.1 cubic inches. It’s hand-crank started and was originally built with a large belt pulley on the output. This one never really worked for a living, however, being used in a tech school in Maine. One might guess it was torn down and reassembled many times in it’s life but Nathan sees no evidence of that and, by the way it runs, it’s a very low-time unit.

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