Killinger und Freund
One motorcycle was discovered by the US Army in the spring of 1945 at a German military installation, but it is not known if this was the original prototype or another Killinger und Freund Motorrad.
The K&F prototype went into storage and was discovered and seized by the U.S. Army at the end of the war. It was taken to the Aberdeen Proving Grounds in Maryland, and was placed on display there for a period of time. Later, it was discovered in a scrap heap and purchased by American collector Harry Buck now in the hands of a scooter club in Ohio.
The K&F engine (pictured below) is as unconventional as the chassis. It is a surprisingly small unit designed to be mounted in the imagefront wheel. It has been described as a three-cylinder two-stroke, but it is far more complex than this. Rather, it is three two stroke singles with their cranks geared to a center drum which carries the clutch and a two-speed transmission.