There is a saying that used to be shared in history circles, with a wry smirk, which has since become a minor cliche: “History is written by the winners”. Hackneyed though it may be, there is a great deal of truth in that old platitude. Be it in politics or in motorsports, odds are the story you know is the one that has been informed by the success of those who came out ahead. In the case of DKW and their series of once-dominant supercharged motorcycles, the company's successes have been drowned out by the tides of history. Some of the fastest, most advanced, and technologically interesting two-strokes of the 1930s have nearly been forgotten due to the company's unfortunate national ties – the once-famous Ladepumpe and supercharged “Deeks” became victims of historical circumstances beyond their control.
The DKW story begins in 1916 when Danish engineer Jørgen Skafte Rasmussen founded the company in Zschopau, Germany. At this early stage Rasmussen was producing steam machinery fittings, the latest of several industrial business ventures he had worked on since immigrating to Germany in 1904. The resource shortages and rationing experienced in Germany during the First World War had inspired Rasmussen to develop a steam-driven automobile as a more economical alternative to gasoline-powered machines, hence the company's name: Dampf Kraft Wagen, the "steam motor vehicle". While the steam car venture failed to take off, the fledgling company found success in an unlikely avenue: a tiny, high-quality 18cc two-stroke stationary engine designed by engineer Hugo Ruppe. Des Knaben Wunsch, as it became known, was sold as a toy engine and soon took the place of miniature steam engines on the tabletops of well-to-do children across Germany.
DKW entered the two-wheeled fray in 1921 with another Ruppe design, this time a 118cc two-stroke auxiliary engine that could be installed on a bicycle. This humble machine was dubbed Das Kleine Wunder, once again preserving the DKW moniker despite the change of tact and presumably allowing Rasmussen to re-use the company letterhead.
It wasn't long after this tentative first step into the two-wheeled marketplace that DKW built its first complete motorcycle, the 142cc Reichsfahrmodell of 1922. The timing proved to be fortuitous as the company was able to ride the wave of newfound popularity for inexpensive two-wheeled transportation following Germany's bout with extreme inflation in the early 1920s. Such was the success of DKW motorcycles that by 1928 Rasmussen purchased a controlling stake in a little automotive manufacturer by the name of Audi Werk AG in Zwickau. The Zwickau factory would subsequently became the site of DKW automobile production, while motorcycle manufacturing continued at Zschopau. By the early 1930s DKW was one of the world's largest motorcycle manufacturers with over 20,000 employees. Two-strokes remained the company's speciality, and DKW became well regarded as a manufacturer of high-quality 'strokers in both two- and four-wheeled applications – it seems unusual today, with four-stroke automotive engines having been the norm for the latter half of the 20th century, but there was once a time when you could find smoky ring-ding mills under the hood of a variety of cars competing with their (admittedly heavier and more complicated) four-stroke counterparts. Through the 1930s DKW produced a series offascinating forced-induction two-stroke V4s that used a pair of integrated cylinders to pressurize the intake charge – the resulting motor appeared to be a V6 but only had four “functional” cylinders, the extra pair of pistons serving as compressors.
With their explosive growth at the end of the 1920s checked by massive debt and the beginning of the Great Depression, DKW needed to re-organize to remain solvent. The solution came in 1932 when DKW and Audi were merged into Auto Union along with Horch and Wanderer. The current four-ring logo used by Audi was the symbol of Auto Union, each ring representing the four manufacturers.
Success in two-wheeled endeavours inevitably results in competition, and DKW was quick to begin producing racing machines to compete in small-displacement categories. During those early days of racing DKW encountered a formidable competitor from rival German marque Bekamo, who produced a series of highly refined two-stroke singles that became famous for being the first "supercharged" production motorcycle. They were designed by (drumroll) Hugo Ruppe – the same Ruppe who had designed Des Knaben Wunsch and Das Kleine Wunder before leaving DKW to found Berliner Kleinmotoren Aktiengesellschaft (Bekamo) in 1922. The Bekamo piston-port 129cc single used a dummy piston and cylinder that was placed opposite the functional piston at the base of the crankcase. It appeared to be an asymmetrical flat twin at first glance but the supercharging cylinder, dubbed the Ladepumpe (charging pump), had no porting or spark plug.
The engine operated on the Bichrome supercharging principle where the swept volume of the crankcase was reduced as the supercharging piston moved up, thereby compressing the intake mix as it swirled through the crankcase. The piston doesn't compress air directly, it dynamically reduces the volume of the crankcase as the intake port opens. The upward movement of the pumping piston was timed to match the downstroke of the main cylinder so it compressed the intake mixture just as the port opened, forcing the charge into the cylinder. This is an effect that is only possible in a two-stroke, where the crankcase serves as the intake plenum. The deflector of the piston-port design angled the intake charge upward into the combustion chamber, preventing the pressurized mixture from being blown straight out of the open exhaust port on the opposite side of the cylinder (a problem called "overscavenging" in two-stroke parlance). The Bekamo also featured a novel adjustable air-assisted scavenging system where an extra port fed fresh air into a chamber inside the piston, after which it would be fed into the cylinder to help push exhaust gas out before the fuel mixture entered.
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