This commercial engine had a clever trick that set it apart: Jalopnik

The Commer TS3 engine, built for Commer trucks from the 1950s to the late 1960s, did not conform to the design conventions of the time. Where most engines follow the familiar blueprints with one piston per cylinder, either arranged in an inline, V or flat configuration, this 3.25-litre two-stroke diesel used three cylinders (the 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 in each cylinder that faced each other and shot in and out like two fists meeting with one punch.

This opposed piston design managed to reduce weight by cutting away cylinder heads and valve train components, as well as the space required to house them. Despite being a sleeker and more compact underbody package, the engine still managed to take on the larger diesels of the time, putting out 105 hp and a stout 270 lb-ft of torque.

Having two pistons per cylinder is definitely cool and all, but it wasn’t this engine’s only trick. A single crankshaft is where the real magic lies in making everything work together. Many opposed piston engines rely on two crankshafts, one for each piston, but Commer’s engineers directed the movements of both pistons through a system of rocker levers and connecting rods that ultimately locked into a single crank below. Keeping everything compact was the first win. The second was to completely eliminate the cylinder head. Yes, you don’t have to worry about the pros and cons of porting for this one. With no valves, cams, pushrods or rocker arms above, the engine avoided many of the failure points that plagued conventional diesels of the era.

The TS3’s two-stroke design is based on the pistons moving close and apart 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-facing piston has a slight timing advantage over the other, closing the ports at just the right time.

The TS3 was especially effective as an all-rounder. Its operation was extremely smooth for a mid-century diesel, thanks to the inherent balance provided by opposing pistons – no counterweights were required. Additionally, Commer’s cab-over-engine trucks were able to maximize seating space without sacrificing power. Three people could sit next to each other, all thanks to the compact form factor. It was also a robust workhorse, which performed well for a long time thanks to its robust construction and a stroke of 20 cm.

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 from a block away. By the late 1960s, Rootes was already developing a more powerful four-cylinder TS4, but the Chrysler takeover saw both engines shelved in favor of conventional diesels. With its electric SUV project recently shelved, it seems Chrysler has a habit of nipping promising prospects in the bud.

The TS3 was compact and brutally simple in all the right ways. Was it strange? Absolute. But it was so brilliant that decades later, engineers and enthusiasts are still amazed at how such a strange design worked so well.