Dunelt two stroke

 Here's an interesting concept for a two stroke. The typical ported cylinder has a step at the bottom, bored to a larger diameter.  The matching piston has a matching larger diameter rim with a second ring. The larger diameter section enhances the pumping action of the crankcase providing a measure of supercharging. The engine was not really successful, probably due to expansion issues with the piston and 1920s metallurgy.

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