We've seen some bonkers engines in our day, and truth be told, this three-cylinder diesel isn't the strangest of the lot. There are plenty of inline three-pots out there, but actually, this is an opposed-piston engine, not entirely unlike the boxer engines you find with Subaru and Porsche. How do you have opposed pistons when there are only three cylinders? It's okay, there are six pistons using those three cylinders, so the math checks out. Wait... six pistons in three cylinders?
If you're confused, don't worry. We haven't even mentioned the supercharger yet. Technically, it's not really a supercharger, but it sort of works like one. Now that you're really confused, let us introduce you to the Rootes TS3, sometimes called the Commer Knocker for its clattery sound at idle. It debuted in the 1950s and mainly powered trucks, buses, and commercial vehicles for several decades in Europe and Australasia. It has quite a story, so sit back as we explain how this truly fascinating engine works.
Rootes TS3: Six Pistons In Three Flat Cylinders
Rootes TS3 Diesel Engine Cutaway
Rootes TS3 Diesel Engine Cutaway
Rootes TS3 Engine Services
In a conventional piston combustion engine, each piston travels up and down in its own cylinder. A single connecting rod links it to the crankshaft. It doesn't matter if the cylinders point straight up, in a V shape, or lay flat – pistons travel to the top of the cylinder, where air and fuel mix and ignite in a combustion chamber, pushing the piston back down. The more pistons you have, the more power you can make. But it also makes the engine bigger, since you need more cylinders.
With the Rootes TS3, two pistons share one long, horizontal cylinder. Instead of traveling to the top of the cylinder to a combustion chamber, they travel inward towards each other. The pistons actually create their own combustion chamber, compressing the air/fuel mix in the middle of the engine. A small connecting rod connects each piston to a massive rocker arm that pivots as the pistons travel in the cylinder. A second connecting rod connects the rocker arm to the crankshaft, basically forming a big U shape. And since it's a diesel engine, there are no spark plugs. The mixture is ignited entirely by the compression as the pistons almost come together.
Rootes TS3 Diesel Engine Diagram
Rootes TS3 Diesel Engine Operation
Rootes TS3 Engine Services
What about the supercharger?
For starters, the supercharger-looking thing is actually called a scavenge blower, and it doesn't add horsepower. Without getting too technical, a roots-style supercharger is basically two rotors that spin in a housing, pushing air into an engine. The blower on the Rootes TS3 injects low-pressure air into the cylinders to help push out exhaust gases, creating a nice, clean mixture for the next round of power. It's called scavenging, and in the case of the TS3, the blower is needed since it's a two-stroke engine: intake/compression happens on the first stroke, with power/exhaust on the second. It's yet another neat factoid about this engine.
Big Power From A Compact Engine
The engine was designed and developed by a division of Rootes Group. This conglomerate had several British automotive brands in its wheelhouse, including some familiar names like Hillman and Sunbeam. A brand called Commer was all about commercial vehicles, and in the post-war landscape of England, a compact-but-powerful engine was needed to fit in its cabover trucks. As we know from Porsche and Subaru, a flat engine can be pretty darned compact while generating plenty of power.
According to Rootes TS3 Engine Services, the TS3 started life as a 3.2-liter engine producing approximately 70 horsepower and 230 pound-feet of torque at a lazy 1,250 rpm. Through its evolution, the engine would grow to 3.5 liters and make as much as 165 hp and 345 lb.ft of torque. Its simple design was also quite robust and easy to maintain, and its size allowed for smaller trucks to still have roomy cabins. There was even a larger four-cylinder/eight-piston version developed, but it never went into production.
Killed By Chrysler
The Rootes TS3 was built through 1974 but succumbed to the march of progress. Chrysler acquired the company in the late 1960s and had warehouses full of Cummins diesel engines that were more conventional in design and arguably more powerful, albeit larger. The TS3 was phased out and further testing of the larger version was canned. But upwards of 54,000 TS3 were built before it all came to an end.
Rootes Group didn't pioneer the idea of a horizontally-opposed engine with two pistons per cylinder. That happened many years prior, but the company's TS3 was a unique design that most decidedly had a successful run. Judging by the numerous videos all over the interweb of these engines in action, there's still a devoted following for what's undoubtedly one of the most interesting mass-produced engines ever built.
Sources: Rootes TS3 Engine Services, The Autopian