Some Old British Trucks Had One Of The Weirdest Diesel Engine Designs You’ve Never Heard Of

Most of the internal combustion car and truck piston engines built throughout history have pretty familiar core designs. The majority of fuel-burning vehicles sold today orient their pistons in inline or vee configurations of largely similar designs. Boxers and “flat” designs are less common, but still feature one piston per cylinder. But here’s a truly strange type of engine out there, and it cranks the weird past eleven. I’m talking about the Commer TS3, a three-cylinder, six-piston diesel “opposed-piston engine” that powered big trucks in Europe. “Three cylinders, six pistons?” Yes.

Some of history’s weirdest engines were developed to fulfill a specific mission. For example, Mazda is famous for its dedication to the Wankel rotary engine, but the firm’s attachment to the spinning Dorito was initially one of necessity. In the 1950s, the Japanese government was considering merging weaker companies to compete better on the global stage. Only companies that had something special going for them would have been able to remain independent. The rotary was Mazda’s saving grace. It was something new and futuristic that, at the time, was believed to be the potential ultimate form of internal combustion.

Sometimes, engines are made because of other constraints. For three decades, Volkswagen made an iconic narrow bank angle so-called “inline vee” VR6 engine. These compact sixes, which had banks so narrow they shared a single head, made their debut in 1991 and promised to pump V6 power into engine bays normally meant to fit transverse inline-four engines.

Less well-known is how the Brits solved their own problems with packaging and durability, and their solution is so wild it’s actually surprising to read it wasn’t somehow the work of a German mad scientist. How do you build a truck with an engine under its cab and still maintain enough space for three people to have comfortable seating? Use a compact diesel engine! That’s what the UK’s Commer did for over a decade with a wild engine.

More Pistons Than Cylinders

The Commer TS3 is almost hard to wrap your head around. It’s an opposed engine, but not in the way you think. Instead of pistons punching out like a BMW motorcycle or a Subaru, these things come at each other from within the same cylinder. That means you have a single cylinder with two pistons in them. Times that by three and a Commer owner could technically joke they have a “three-cylinder flat-six” and they wouldn’t be far off.

Commer might not be a known entity here in the United States, but it used to be a big deal in places like the United Kingdom and New Zealand. Commer was founded in 1905 as Commercial Cars in Luton. The company was the brainchild of Julian A. Halford, who conducted experiments on the transmission invented by Charles Montague Linley a couple of years before. Halford decided to build a vehicle around the Linley transmission and Commercial Cars was the vehicle to build these cars.

The company would become known for its commercial trucks before eventually falling on hard times in the 1920s and eventually getting sold to Humber Ltd. in 1926. Commercial Cars found itself renamed to Commer and kept on trucking until 1931, when Rootes Group attained 60 percent control of the company.

For most of Commer’s existence, it built reliable but otherwise forgettable commercial vehicles. The exception to that is the trucks that would be fitted with the Commer TS3, an engine that remains an icon among older British truck fans.

Engineers of the past found a clever way to deal with size constraints as well as the heavy weights of early diesel engines. If they needed to fit engines into relatively small pockets, they designed small engines to fit. Tilling-Stevens had a flat-eight engine in its commercial vehicles and the Napier Deltic, perhaps one of the most bizarre engines in history, was an opposed-piston engine set up in a triangle and found use in naval and rail service.

They weren’t the only ones, the Swiss Sulzer ZG9 was an opposed-piston engine before World War II that found a life powering generators. Meanwhile, the Junkers Jumo 204 of 1929 was another opposed-piston diesel engine and it was bolted to aircraft. There were opposed-piston engines as early as 1905. Scottish car manufacturer Arrol-Johnston had a rope-start opposed-piston engine back then.

The opposed-piston fever even hit America, where Ransom Eli Olds sought to solve the problem of early diesels being so heavy. His diesel would dramatically cut down on weight with a radical new design. Instead of the typical piston engine, which had its pistons firing up and down in their own cylinders, his would cut down on material by having the pistons fire horizontally.

This was done because, as Hemmings writes, diesels of nearly a century ago weren’t just insanely heavy, but they also had a need for a more efficient exhaust gas scavenging process. Olds believed the solution was an opposed-piston diesel, from Hemmings:

Olds conceived a horizontal two-piston-per-cylinder single-crankshaft two-stroke direct-injection diesel engine that used hefty rocker arms to transfer the motion of the pistons to the crankshaft. The fuel injector would be located in the center of the cylinder, intake and exhaust ports would be located at opposite ends of the cylinders, and each pair of opposed pistons in a cylinder would be timed 15 degrees apart to keep the exhaust and intake ports opening at different times. The advantage of such a configuration, Olds argued, comes in its compactness, reduced weight, and reduced cost of manufacture:

A further advantageous feature of this invention which contributes materially to reducing the weight of the engine without sacrificing rigidity resides in the novel means provided for relieving the cylinder block and associated parts of the engine from the stresses resulting from the relatively high compression pressures developed in the cylinders.

So, for how weird the Commer TS3 is, it wasn’t an unheard of idea in its day. Rootes TS3 Engine Services, a New Zealand company dedicated to servicing, restoring, and documenting the history of the TS3, published the full scoop on how these engines came to be. According to a piece on the site, development on the Commer TS3 began in around 1946 with a three-person team over at Humber. Quickly, this team expanded to 13 people and was renamed the Rootes Diesel Engineering Division. Leading the project was Eric Coy, Chief Engineer of Humber. The engine Coy and his team built is unlike any engine you can put into a car or truck today.

Over a production period that lasted nine years, the team created a two-stroke engine that featured three cylinders. In those three cylinders were two pistons each, which ran toward (compression) and away (combustion) from each other. These pistons used a series of rocker arms and connecting rods to meet the engine’s single crankshaft.

In operation, a supercharger forces 6 PSI of compressed air into the intake manifold. During the compression stroke air enters one end of the cylinder with one piston while the other piston, which is slightly ahead of the other piston, closes the exhaust ports on its way in. A swirl of air is created in the cylinder as the compression stroke continues.

As both pistons close on each other and the engine reaches inner dead center (this engine’s equivalent of top dead center), fuel is injected from the middle of the cylinder. The heat and pressure generated during the compression stroke ignite the fuel at about where the pistons meet, starting the power stroke.

As the pistons pull away from each other, the exhaust ports open, blowing exhaust gases out. Once the pistons reach their furthest distance apart, the intake ports open, pushing in compressed fresh air and scavenging the rest of the exhaust gases. Then, the cylinders start coming back at each other, closing the exhaust ports and starting the process all over again.

Rootes TS3 Engine Services notes that opposed-piston engines have several advantages over the typical diesel engine of the era. The Commer TS3 didn’t have cylinder heads, head gaskets, rocker cover gaskets, camshafts, valves, or pushrods to fail. Further, the engine didn’t have the ancillaries necessary to run valves, which means even fewer points of failure. It’s also noted that the TS3 was even further optimized by the fact that sure, it had six pistons, but only three cylinders. That meant fewer injectors. Finally, due to the opposed-piston design, the engine naturally provided its own equal and opposing forces, negating the need for counterbalances in the crank.

All of this added up to what Rootes TS3 Engine Services claimed was “impressive engine life” and “very high levels of mechanical reliability.” The service center also notes that the engineers behind the design specified the engine to have unusually high quality materials and that tolerances were so high that it has been hard to create replicas of these engines in the modern day.

It all becomes even more impressive when you learn that the British engineers achieved all of this with calculations written down on pads in pencil with aid from logarithms and mechanical adding machines.

The Commer TS3 made its debut in 1956 and these 3.25-liter engines featured a common configuration of 105 HP and 270 lb-ft of torque. A later version saw displacement move up to 3.5 liters with a mild increase in power. While these numbers aren’t impressive today, they were great for such a small truck engine back then. These engines made the sort of power found in bigger diesels, but were small enough to fit into nooks and crannies.

Rootes TS3 Engine Services claims that part of the secret sauce behind the good power was the fact that this engine enjoyed whopping 8-inch strokes. The firm also says that crazy long 8-inch stroke is part of the engine’s durability. The shop claims that TS3s with worn rings and damaged other “critical” components will continue to start and run every day. They might be down on power, but TS3s were known for taking epic beatings and still starting afterward.

Australian trucking news site Roadtrains.com.au adds context to just how advanced the TS3 was for its day:

Yet it wasn’t until I read a report conducted by Transport Engineer magazine in the UK that it truly hit home how advanced the Commer TS3 Diesel engine was for its time and why it endured almost two decades of production. In the Transport Engineer issue dated August 2001, they conducted a noise and emissions test between a MAN 18.224, Isuzu NQR, Mercedes-Benz Sprinter 413CDI, and to make it interesting, a 37-year-old TS3 Commer. The average drive-by noise at 50kph results was unexpected; MAN 84dbA, Isuzu 79dbA and Commer 78.4dbA. The MAN regained some face in the emissions testing proving to be the most environmentally friendly with only 7 particulates (mg/cu m). The Mercedes-Benz Sprinter result was 11 particulates, and the Commer TS3 was 55 particulates. Nevertheless, when it came to fuel economy, the 37-year-old TS3 Commer made the podium amid a field of young upcoming stars and wannabes.

That compact size was also important. Commer TS3s were so small that they were able to fit under the cabs of Commer and Karrier trucks leaving enough space for three men to sit relatively comfortably in said cabs. Of course, an engine as unique as the Commer TS3 also had a wicked sound and listen:

Export models of the Commer TS3 had a different, undamped compressor that allowed the engine’s timing gears to clack. After enough wear, the gears caused the engine to produce a knocking sound. This sound was present in models found in a place like New Zealand, but not back in the UK. There were enough of these trucks around that they gained a nickname of “Commer Knockers” in New Zealand. That nickname became so well-known that you’ll find it used all over the Internet today.

Commer had huge plans for its opposed-piston diesel engine. The company began work on the TS4, a four-cylinder, eight-piston engine. Allegedly, this engine had the potential to blow the competition out of the water. Commer even put 1.2 million miles on a test engine.

Unfortunately, the Commer TS3 and its sequel became dead ends when Chrysler purchased Rootes in 1968. Here’s another sound clip of the TS3:

Chrysler favored conventional diesel engines and this would not only spell the end of TS4 development, but also kill off the TS3. Eventually, the Commer name itself was even scrubbed away and replaced with Dodge-branded trucks.

Amazingly, worldwide opposed-piston diesel development didn’t end with Rootes. Leyland made its own opposed-piston diesel, as did the Soviet Union.

In the modern era, Diesel Air Ltd in the UK created the Diesel Air Dair 100, a rare opposed-piston diesel for use in light aircraft and airships. Volvo filed for a patent for an opposed-piston diesel in 2017 while in recent years, Cummins signed a contract with the U.S. Army to produce the Advanced Combat Engine, a modular opposed-piston diesel architecture. American company Achates Power has also been developing opposed-piston diesels for nearly two decades, though you cannot buy a vehicle with the company’s engines yet.

None of these engines are mainstream. It’s not like you can roll down to your Ford dealer and pick up a Super Duty F-350 Power Stroke with an opposed-piston engine. But for some, the promise is still out there. Archates Power claims its diesel engine is 30 percent more efficient than a typical comparable diesel. Cummins says its 14.3-liter opposed-piston powerhouse makes 1,000 HP and 2,424 lb-ft of torque, but you have to don olive drab to experience it.

Yet, at the same time, diesel is in a weird place in itself. Automakers and truck makers alike have their eyes set on a future with alternative energy. Diesel remains king in the heavy duty space for the foreseeable future, but the expectation is that one day, an alternative technology will be ready to take over. Who knows where diesel will lead. What I can tell you is that the so-called Commer Knockers were delightfully weird engines and it’s amazing they were made in the first place.