In the twenties, Zundapp only dealt with two-stroke. In 1930, however, the four-stroke machines S 500 Tour and the S 500 Sport came on the market. These two machines had a 4-valve (!) Rudge engine of 499 cc. The Touring had 18 hp and the Sport achieved 22 hp. The customers of Zundapp not only required two-stroke, but also four-stroke, hence the choice for the S 500 series with a motor from another manufacturer mounted in it.
1931 was the last year for the S 500.