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In 1958, Walter Zeller ordered a very special BMW from the factory, to be built entirely to his specification and to suit his riding style. As Zeller had been the principal Works racing rider for many years, gaining several German championships and 2nd in the World Championship in 1956, BMW management granted him this solitary exception to their rule of 'no custom orders'. That the factory presented the finished product as a gift for his services to BMW is the stuff of legend; the ultimate BMW trophy.
The machine is a mélange of interesting parts; a 600cc ohc Kompressor motor from Max Klankermeier's '49 sidecar racer (blowers were still allowed in German national championship races after '48), housed in a special Rennsport-based swingarm frame, utilizing telescopic forks from the 1951 Works development racer, instead of the Earles type on the racers and contemporary BMW roadsters. The forks are a very interesting choice; did Zeller feel that his racing BMWs handled poorly with their Earles forks? If Zeller 'voted with his feet', the answer is yes, he preferred a standard telescopic fork to the Earles item. Quite a statement for a Works rider to make, actually! To quote Josef Achatz (the foreman of the build team for this bike), "Walter preferred telescopics".
Lighting was added to the front and rear, again interesting choices, for while the headlamp is as per the roadsters, but with a tachometer replacing the speedo, the taillamp is a seriously prewar item, as used on mid-30s machines; the Bosch equivalent of the ubiquitous MT110 Lucas taillamp, used on just about every British bike in the 30s and through WW2.
The tank is as per the Works machines, as is the seat, while the exhaust is the fishtail type as used on the R51 and other models pre- and post-war. It would have squelched the power of the blown engine, if any baffles were fitted, which is an open question; why have a supercharged engine with a power-strangling muffler? But, the original TUV specification papers state the sound output as 73db; terribly quiet for a racing bike. Top speed is quoted at 112mph (180kph), which is certainly down on any of the supercharged racers, which were at least 30mph faster through the speed traps. Weight is quoted in the TUV document at 388lbs (176kg), but Zeller had the machine weighed at a steel factory (St. Anna-Huette; Zeller's family business), which quoted 317lbs. This is very close to the '39 TT-winning bike of Georg Meier, which was 30lbs lighter than the competition.
Zeller kept the machine for many years, and used it occasionally on the road. As there is no kickstarter, he bump-started the bike; in this, his racing years gave him expertise. According to news reports, it took him 'ten or a dozen starts' to sort out the right combination of throttle, magneto, and air levers - after this, his technique was flawless. Once the bike was warm, the plugs would be changed to a harder grade... it's clear this one-off BMW required a bit more forethought to ride than the typical 'no fuss' flat twin. As there was no room for a generator, the lights are total-loss, making this strictly a daytime ride.
Contrary again to the TUV papers, Zeller reported the bike would acclerate from 0 to 100kph in under 5 seconds, and that 200kph (124mph) was 'no problem'. In 1958, there was only one other road-going machine capable of such speeds, and the Vincent Black Shadow had double the engine capacity, was 140lbs heavier, and had been out of production for 3 years! Zeller must have cut quite a romantic figure on the Alpine roads he favored (Queralpenstrasse and others), passing literally everything on wheels, drawing a large crowd whenever he stopped, then bump-starting away, leaving only a fantastic noise, and a slight haze from the 2% oil mix lubricating the supercharger.
Alas, times were difficult for Zeller's family business in 1963. He had been pressed by a persistent pesterer, a schoolteacher no less, to sell the machine. Norbert Reisbeck phoned Zeller every month for over a year, asking again and again if he could buy the magical BMW. In what must have been a black month, Zeller caved in, and sold the machine for 7,000DM in 1963.
(The source of photos 2-6 are from an article on this machine by Ernst Leverkus in The Classic Motorcycle, April 1986)