Commer TS3 diesel?
a Rootes Compressor, but where are the pistons...
Well, it was spelt Roots (nothing to do with the Rootes Group), and here's a picture of the innards. I note that Wikipedia claim the design was used by Rootes because a) they had taken over Tilling-Stevens whose design it was , and b) they wanted a "cab-forward" truck and it would be necessary to have an engine which would fit beneath the floor. Other manufacturers fitted the engines in the middle of the cab under a cover.
It was a 2-stroke, 3 cylinder diesel engine with six pistons using a complex crankshaft/conrod arrangement, and it was supercharged. Complex doesn't begin to describe it. And the noise!
As far as the general public was concerned, the most noteworthy thing about this engine was its unique exhaust note. No use trying to describe it, but it's really, well, interesting. Have a listen on You tube by searching for 'Commer T3 running', or something similar. I recall hearing these lorries as a kid and the sound is unforgettable! 
Ditto. I lived on the outskirts of Norwich, and a brand new livestock market was built in the vicinity (at the time it was the largest in Europe). In those days smaller herds were still taken to market by walking them, but the more affluent farmers used livestock hauliers, and one of them, based at Snetterton Heath airfield, went by the name of Foulgers, and used Commers. They went past my house every Saturday to the market, and I could hear them from inside my house.
It's quite clear why the engine is known as the "Knocker". Just extraordinary.
