Two stroke Thursday, in opposition

Let’s follow on from last week’s DKW supercharged two strokes with another.

This is rather different, because it’s an opposed piston design. Have a look at this animation.


We have two cylinders, two cranks and four pistons. The idea is that air enters at one side, gets itself combusted and then leaves from the other side, so that each cylinder has an inlet and an exhaust piston.

Here’s the only picture I could find of a complete bike, made just after WW2 by IFA DKW, a socialist workers’ paradise owned entity which had taken over what remained of DKW’s operations after the Russians had seized anything of value.

As far as is known the few bikes they made found their way to the Soviet Union not to be seen again. With one exception.


One engine was spirited away to the West and fitted to a pre war DKW frame, a process which involved turning the engine 90 deg from its intended orientation so it went from a BMW layout (longitudinal cranks, transverse cylinders) to the opposite. You can see how the supercharger - the cylindrical device above the engine - changes its orientation to match. It was raced for some years, was caught up in a ban on supercharging and vanished until 1991 when it reappeared and was restored by Darmstadt University who put it on their dyno (every university should have one) which revealed 55 bhp at 8,500 rpm, quite something for a 250cc engine designed more than forty years before.


If you want to see it, take yourself here.

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