Vintage Opposed Pistons

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.

Jumo Wrestling

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.

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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.

This Fairbanks-Morse generator set dates to the early 1950s, possibly 1952. It’s rated for 200 KW at a whopping 2400 volts. It was used on the R.J. Reynolds estate on Sapelo Island, Georgia, until power lines were run from the mainland. The engine was rescued in the mid 2000s by a group of Coolspring volunteers, saving it from the scrappers. In this application, the 38F51/4, five-cylinder engine is rated at 300 horsepower at 900 rpm. That’s a calculated 1751 lbs-ft at 900 rpm. In stationary use it could produce up to 413 horsepower at 1200 rpm, When used as a marine propulsion engine, it could be seen rated at 375 horsepower at 1200 rpm.

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.

A cutaway of a typical F-M 38D OP diesel. It differs in some respects from the 38F highlighted in the story. The D-models have two injectors while the F have only one, plus some differences in the internal exhaust system. The Model 38s are all two strokes and have no valves, only ports in the liner. The scavenging (intake) ports are at the top of the cylinder and are covered or uncovered by the upper piston. The exhaust ports are on the bottom and covered or uncovered by the lower piston. The upper and lower pistons in each cylinder are on the same stroke. On the compression stroke, they meet in the middle, the injector sprays just before they reach TDC, ignition begins and the pistons are pushed apart after TDC. The ports are located so that the exhaust ports are uncovered before the intakes (by about 12 degrees of crankshaft rotation). A Roots style blower pushes air into the cylinder at 4-6 psi once the intake ports are uncovered and scavenges the cylinder for the next go-round. Later engines also had turbochargers and that really gave them a boost in power. Note that the engine block is built from plate steel welded together.

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.

F-M offered skid-mounted generators sets in the ‘50s and this one was rated at 250 KVA (thousands of volt-amps, about 200 kilowatts) and 2400 volts. Why the high voltage when the building were at 120 volts? It was a commercial generator and that high voltage was useful when the generator was feeding a grid, as this one did on Sapelo Island. It’s just like the local transmission lines that feed power to your house at a high voltage (typically 13,800 volts these days). High voltages minimize line loss in longer distance power transmission and transformers are used to step the voltage down where the lines reached the buildings, in this case from 2400 to 120. In this view, you can see the blower assembly and it’s four oil bath air filters. The blower is driven from the upper crankshaft.

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.

One of the Fairbanks-Morse Train Master locomotives. A couple of different version of this were built, this one being the Model H-24-66, a switcher version. Built for Canadian Pacific in 1953, it weighed 170 tons and was 66 feet long The 38D81/8-12 displaced 12,443 cubic inches and was rated for 2400 horsepower at 750 rpm. With the big DC generator driving six DC traction motors, it could generate 112,000 pounds of tractive effort. Top speed was 65 or 80 mph, depending on which traction motors were installed. According to sources, this is the only surviving operational F-M Train Master and is run by the Canadian Railway Museum in Quebec, Canada.

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.

The injectors are positioned midway in the cylinder liner. In the F series engine like this, there is only one injector as seem here but the D-Series had another on the opposite side. This area is normally open, though there were covers available in some applications. Camshaft driven unit fuel pumps are above this area and are controlled by the rack you see in the upper portion of the opening. The round openings access the exhaust ports in the liner and there is a matching set on the other side, in this case mounting thermocouples to measure EGT.

No Epitaph

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.

The engines were air start and the controls were pretty simple.

The Fairbanks-Morse logo back in 1952 still harkened to their corporate roots building scales. They were still in that business until 1988, when that division was sold off to be an independent entity, Fairbanks Scales.blower is driven from the upper crankshaft.

Source

Coolspring Power Museum
179 Coolspring Road Coolspring, PA 15730
814-849-6883
coolspringpowermuseum.org