For today’s Two Stroke Thursday we’re going to explore the Commer TS3, otherwise the Commer Knocker. Why? Watch this

The TS3 was a three cylinder opposed piston two stroke diesel with rocker arms and extra conrods linking each set of pistons to a common crankshaft, a design presumably chosen to avoid having to fit two cranks geared to a common output shaft.

It looked and ran just like this

The origins of the TS3 were in the 1930s when German maker Junkers designed a two stroke diesel of unusual design for use in aircraft. Napier, who had an unusual penchant for the weird and not always wonderful, took out a licence and redeveloped it as the Culverin. After WW2 it was obvious to Napier that the days of large piston engines in planes were over (but not so obvious as to prevent them heading up the blind alley that was the Nomad ) and so they decided to modify it to a simpler three cylinder design. Production was carried out by Tilling Stevens from which we get the name.

Tilling Stevens were bought by car and truck maker Rootes Bros. who had rather specific requirements which the TS3 seemed to meet. They needed a better diesel, they wanted to build the forward control trucks (cab overs, in American parlance) which were fast becoming the norm and they wanted something cheap, reliable and economical. The TS3 seemed to fit the bill and the flat design meant that it would fit an underfloor location well.

Rootes took some care to make the TS3 easy to work on and so the trucks using it had inspection panels in the floor and each side of the cab. Combine these with access via the front and you could replace everything bar the block and main bearings with the engine in situ.


It turned out to be quite successful in truck use, rather less so on buses due to the noise and the eventual availability of a bus chassis based on the Ford Thames with a quieter four stroke.

It was, by the standards of the day, reliable, durable and relatively economical at about 20 mpg (Imp). It did need new piston rings at around 100,000 miles but the easy access meant that this was a job that could be done in less than a day provided you were up for crawling into an inspection panel with your legs dangling out. Like other two strokes it could run backwards, an eventuality that was usually avoided by designing the fuel pump to work only the correct way but accidents did happen. In this case the blower would suck, air would enter via the exhaust, exit via the air cleaner and proceed to fill the cab with fumes.


Production continued until 1972 and would have kept going for a while longer had Rootes not been bought by Chrysler. The latter had a plan with Cummins to make a four stroke diesel (not a good one as it turned out) and the TS3 didn’t fit with the plan. Production ceased and all prototypes of the planned TS4 were ordered to be destroyed. As it happens a few were hidden away and at least one is running.

There are occasional plans to produce updated versions but as of now they haven’t come to anything.