This Commer Engine Had A Clever Trick That Set It Apart

The Commer TS3 engine, built for Commer trucks from the '50s into the late '60s, didn't conform to design conventions of the time. Where most engines follow familiar blueprints with one piston per cylinder, either arranged in an inline, V, or flat configuration, this 3.25-liter two stroke diesel used three cylinders (pros and cons of which can be found here) and six pistons. Instead of pistons moving up and down to a single shared cylinder head, the TS3 had two pistons facing each other in each cylinder, firing inward and outward like two fists meeting in a punch.

This opposed piston design managed to reduce weight by cutting out cylinder heads and valve train components, as well as the space needed to accommodate them. Despite being a leaner and more compact underfloor package, the engine still managed to go toe-to-toe with larger diesels of the time, delivering 105 horsepower and a stout 270 lb-ft of torque.

Having two pistons per cylinder is definitely cool and all, but it wasn't the only trick up this engine's sleeve. A single crankshaft is where the real magic lies in getting everything to work together. Many opposed piston engines rely on two crankshafts, one for each piston, but Commer's engineers routed both pistons' motions through a system of rocker levers and connecting rods that ultimately tied into one crank below. Keeping everything compact was the first win. The second was eliminating the cylinder head entirely. Yeah, no need to worry about the pros and cons of porting for this one. Without valves, cams, pushrods, or rockers overhead, the engine avoided many of the failure points that plagued conventional diesels of the era.

The TS3's two-stroke design relies on the pistons moving near and away from each other to create power. Intake and exhaust functions were handled by ports in the cylinder wall. To prevent fresh air from blowing straight out of the exhaust, one exhaust-focused piston led another slightly in timing, closing ports at just the right moment.

The TS3 was especially effective at being a jack of all trades. Its operation was extremely smooth for a mid-century diesel thanks to the inherent balance provided by opposed pistons — no counterweights needed. Moreover, it allowed Commer's cab-over-engine trucks to maximize seating space without sacrificing power. It could accommodate three people sitting abreast, all due to its compact form factor. It was also a tough workhorse, running well over long periods of time as a result of its rugged construction and eight-inch stroke.

Export versions with undamped compressors developed a distinctive rattle. This unmistakable metallic knock earned the TS3 its enduring nickname, the "Commer Knocker." Drivers could pick one out from a block away. By the late '60s, Rootes was already developing a more powerful four-cylinder TS4, but Chrysler's takeover shelved both engines in favor of conventional diesels. With the recent shelving of its electric SUV project, it seems Chrysler has a habit of nipping promising prospects at the bud.

The TS3 was compact and brutally simple in all the right ways. Was it strange? Absolutely. But it was brilliant enough that decades later, engineers and enthusiasts still marvel at how such an odd design worked so well.