Why The Commer Knocker Might Be The Strangest Engine Ever Built – SlashGear

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The opposed-piston concept is hardly revolutionary; the Fairbanks-Morse 38 1/8 has been powering marine vessels since World War II. French engineer Eugene Brillié was designing opposed-piston engines as early as the 1920s. The DS3 engine that Commer utilized was built by the Rootes group, which owned the Hillman and Humber brands and, at times, built bodies for Rolls-Royce and Daimler, among others. 

The Commer Knocker differed from other opposed-piston engines in that it had one crankshaft instead of two. In the TS3, one piston is designated as the exhaust piston, and the other serves as the air intake piston. The exhaust piston had a much shorter travel distance to make sure its port was sealed when air was being pulled into the cylinder. This quirk set the TS3 apart from other opposed-piston engines, along with the large lobe-shaped blower that captured exhaust gases and forced them back through the intake manifold.

The design was remarkably powerful for its size: the original 3.25 liter TS3 put out 105 horsepower and 270 lb-ft of torque, and a 1964 upgrade boosted those figures to 117 hp and 310 lb-ft. 

The TS3 remained in production until 1972, when the four-cylinder TS4 replaced it. By then, Chrysler’s gradual acquisition of the Rootes group had already begun, spelling the end for the Commer Knocker.

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