It’s hard to think of a more eye-catching, unusual conversation starter than the shaft-drive Sunbeam S7. It was developed as a BSA war reparations project with designer Erling Poppe hired to “de-Germanize” the BMW R75 for sale in England under the Sunbeam brand, which BSA had acquired in 1943.
Poppe chose to use a 500 cc vertical inline twin instead of BMW’s horizontal boxer engine. It was a good idea, except that the new overhead-camshaft unit was so tall that BMW’s reliable bevel-gear final drive wouldn’t line up, and was ditched in favor of an under-slung worm drive made of bronze. This design proved short-lived in a sporting 94 mph prototype, to the S7 became a more sedate 25 bhp cruiser with a top speed of about 75 mph.
The first batch of S7s were a curious mix of German and American styling, with a giant sprung saddle, sprung front forks and plunger rear suspension, balloon tires, wide bars and heavy fenders. The brake and clutch levers were hinged at the end of the handlebars, with the cables concealed inside. The front and rear wheels were interchangeable, though this was of no clear benefit unless one carried a spare wheel.
The fit and finish (available in black only) was excellent, but the price of about $750 was prohibitive, about double that of a 350 cc BSA. It was no wonder that only 2,000 S7s were sold, before a pair of revised models was launched in 1949. The S7 DeLuxe was offered in black and mist green and fitted with telescopic forks and normal levers. The faster and cheaper Sunbeam S8 had smaller fenders, bigger wheels, and an aluminum fishtail silencer. It was available in black, mist green and gunmetal gray. Production of the S7 DeLuxe and S8 ran through 1956.
A Sunbeam is bound to draw attention at any bike gathering, as there are few in the U.S. Potential buyers will likely need to shop in the UK, where an extraordinary number survive – an estimated 10,000 of the 16,000 built.
The first S7s are the most valuable of the three models, like the Series A Vincent Rapides. Spares for this model are extremely expensive, as components are generally not interchangeable with the S7 DeLuxe. A would-be owner who plans to ride his bike might then opt to choose the DeLuxe as parts are cheaper. The S8 was, and still is, the least expensive option, sold as a sports model with larger wheels and smaller section tires, and 10 mph higher top speed.
Only the first few years of S7s have matching numbers and none of the DeLuxe or S8s carried such numbers from the factory. Potential purchases must have a working dynamo, a complete distributor and cap, fenders, tool box and a functioning Lucas Altette horn, as these are the hardest items to find. Original saddles can be tricky to locate as well, and the right-angle drive speedometer is expensive.
Accepted updates include a larger sump, BSA eight-inch front brake and a 12-volt alternator to replace the feeble dynamo. Beware of using the wrong oil in the final drive as some sulphurous gear oils can actually dissolve the bronze worm gear.
1951 sunbeam s7 deluxe Info
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