Fairbanks-Morse Model 38
By Jim Allen
How do you fit ten pistons into five cylinders and make a running diesel engine? Well, the diesel engine manufacturing community has been doing that since the early 1930s with opposed piston engines. One cylinder, one combustion chamber, two pistons and connecting rods and two crankshafts. The two piston crowns face each other and are timed exactly the same to compress and fire at the same time. You get something near twice the work from each firing event, though there are some tradeoffs in terms of complexity.
The opposed piston diesel made a big splash when it debuted in the 1930s, but it wasn’t a new idea. It goes back to 1881 and the dawn of internal combustion and the unsuccessful Atkinson differential engine, but it was barely on the same branch of the family tree of what came later. The Ochelhäuser engine, which was produced in some numbers, is in the same boat, with the second piston used to operate the induction system. There were others but the one that started the branch we are climbing out on was built by Dr Hugo Junkers, who started experimenting with opposed piston gasoline engines in 1913. As it relates to diesels, his contribution was the Junkers Jumo series of aircraft diesels.
We spoke about the Jumo in the December 2021 Vintage Smoke on aircraft diesels. Dr Junkers started the development of opposed piston diesels in 1926 and this eventually resulted in a line of legendary Jumo six-cylinders which debuted in 1932. At the time, they were mostly used for Zeppelins (dirigibles), though some were installed in heavier-than-air aircraft as well. They also found a home as a marine engine during and after World War II.
The Big OP- Fairbanks-Morse Buys In
When the word was out about Dr Junkers’ opposed engine design, Fairbanks-Morse (F-M) bought a license to use and adapt the design. By 1933, F-M had started work developing new lines of railroad and marine diesel engines. Their first opposed piston (OP) prototypes were running in 1934 and a 5 x 6-inch bore and stroke six cylinder engine was put into railway service as a test. An endurance test that year of a 1000 horsepower eight cylinder, 8 x 10-inch bore and stroke caught the attention of the U.S. Navy, who saw them as an optimal submarine diesel.
Work continued on the OP line for the next three years. Among the most crucial highlights was how the crankshafts were connected. Several methods were tried, helical gears and Morse silent chains among them. In the end, a fairly complex spiral bevel gear arrangement was designed and it looked a lot like two ring and pinions connected at the pinion heads via a shaft.
By 1937, the OP line was ready for prime time. The final designation was Model 38… for the year it was formally introduced, 1938. A new section was built to manufacture them in the Beloit, Wisconsin, factory. The first Model 38s had an 8-1/8-inch bore and a 10 inch stroke and their full designation was 38D81/8, sometimes with their cylinder count behind that (e.g. 38D81/8-8 for an eight cylinder). They were initially offered in 5, 6, 8, 9 and 10 cylinder configurations. The nominal rating was 150 horsepower per cylinder at 720 rpm. The first customers were planned to be in the railroad industry and the power density of the Model 38 made them a great fit in the growing diesel locomotive market but success there was going to be uphill. Electro-Motive Corporation (owned by GM) had just about steamrolled the diesel locomotive market with it’s Winton-powered diesel-electrics. Some progress was made in the rail market and then World War II came along.
Dive, Dive, Dive!
The U.S. Navy was ready for the Model 38D81/8 but a key development made them a customer… a direct reversing version… which came in 1939. Sixteen were delivered in 1941 with an order for 90 more. Depending on the submarine, these were either 9 or 10 cylinder units making 1600 horsepower intermittent and 1,280 horsepower continuous at 650 rpm. WWII subs being diesel electric, they were used to run generators and produced 1120 KW maximum and 900 KW continuous. During the war, F-M built 1,650 of these 36 ton engines, at a point building one per day.
On and Off the Rails
Once the war was over, F-M worked on locomotive designs, building a small number of prototypes and test models to be tried in the field. They did well and F-M hit the railroad market very hard in 1950 with a line of diesel locomotives. Soon after the war was over, the H-10-44 cab units debuted, powered by a 1200 horsepower 6 cylinder Model 38. It was a modest success and several other models were produced. They doubled down in 1951 with the Train Master H-24-66, a six axle road switcher powered by a 2400 horsepower 12-cylinder Model 38. At the time, it was the most powerful diesel locomotive on the market and could out accelerate anything else out there. Despite raising diesel loco benchmarks very high, big sales did not materialize. Most of F-M’s sales were in the switch engine category.
Rail historians put F-M’s lukewarm impact in the rail market down to a couple of primary reasons. First, as it relates to the Train Masters, high power diesel locomotives were not yet fully embraced and lots of big steamers will still going strong. Probably the biggest reasons came from the maintenance side. While most historians agree the F-M OP engines were very reliable, it can’t be denied that they were complex vs the more common Winton-designs (later known as EMD) in the Electro-Motive units and other more conventional designs from various manufacturers. The maintenance shops of the various rail lines were leery of the extra complexity of the OP engines. It was reported that maintenance shops of the lines that used the OPs soon adapted to the complexity and had few problems making the switch.
From the records we found, it looks as though F-M built 1,289 locomotives, with another 177 built by licensees or in collaboration with other manufacturers. That was evidently a little too modest for F-M to stay in the game and they exited the train market in 1959. In just a few years, the F-M diesels might have been a better fit so perhaps the old adage is true… timing is everything. Marine and stationary became the main Model 38 markets from then on.
The Li’l OP
Going back to the beginning, F-M developed a smaller 5 x 6-inch more and stroke OP engine. Soon nicknamed “The Li’l OP,” the production version debuted in 1939 with a 5-1/4 x 7-1/4 inch bore and stroke. It shared the same basic design features as its bigger brother and was listed with a nominal rating of 50 horsepower per cylinder at 900 rpm, later rising to about 75 horsepower per cylinder. It shared almost the same path as the bigger unit, marketed as a rail (though we did not see any locomotives listed as using it) and marine engine with a stationary engine side job. Like it’s bigger brother, it became a staple in the marine and stationary markets The WWII Navy liked the 5-1/4 Model 38 and so did the stationary markets. It was in production into the 1970s at least.
Despite those hiccups in the railroad industry, the Model 38 has had a very long service and production life… from 1938 until today, 84 years! The 2021 F-M marine catalog lists 6, 9 and 12 cylinder Model 38 engines making between 2100 and 4860 horsepower. A recent stationary and rail catalog has similar listings. These new engines are dual fuel, using mostly natural gas (around 95 percent) with diesel used for pilot ignition. They have exhaust treatment and emissions are reduced 95 percent from the old style engines. The dual fuel idea is nothing new to F-M or the Model 38, with examples sold as early as 1952 that used a combination of natural gas and diesel. Yes, the Model 38 OP engines were complex but unlike some other equipment that failed for being overly complex, they stood the test of time despite their complexity.
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