The Sunbeam S7

The Sunbeam S7 was a British motorcycle designed by Erling Poppe.Built in Redditch, the engine layout was an unusual in-line 500 cc twin which drove a shaft drive to the rear wheel. The inline engine made this technologically feasible - horizontally-opposed ("flat") twin engine. The early S7 was expensive and over engineered, which is why it is now the most sought after and commands a premium over the S7 Deluxe and the S8, which were produced with less features to reduce costs while retaining many of the innovative parts of the early Sunbeam and updating some ideas.
Three models were produced, the S7, S7 'Deluxe' and the S8. The original S7 (the 'Tourer') (2,104 produced from 1946 to 1948) was expensive and did not sell well. In 1949 the S7 was updated to become the S7 deluxe (5,554 produced) and the S8 (8,530 produced). Both had new cylinder linings, redesigned frames and increased oil capacity.S9 and S10 models were planned but never made as BSA decided to concentrate on the more traditional twins.
Some early models of the original S7 were produced in black but most in the now familiar 'Mist Green'. The S7 Deluxe came in either 'Mist Green' or black and for export abroad BSA supplied Sunbeams in any colour.
Erling Poppe’s design was originally based on a captured BMW R75 but Sunbeam didn’t want the S series to look too ‘German’ so an in-line OHC, parallel twin was designed instead of a flat twin ‘across the frame’. Serious problems with vibration made the new Sunbeams bikes uncomfortable to ride and all production originally sent to South Africa was recalled. The excessive vibration was cured by mounting the engine on two bonded rubber engine mounts.Another problem area was the shaft drive, which had a 'worm drive' in place of the BMW bevels and tended to strip under power. Sunbeam's solution to this was to reduce the power to 24 bhp which did nothing to help post war sales.
The Sunbeam Motor Cycle Club is one of the longest established in the UK and was founded in July 1924 at the London showrooms of John Marston Ltd in Holborn Viaduct who made the Sunbeam motorcycles in their factory at Wolverhampton.The Sunbeam Motor Cycle Club is, however, a sporting motorcycle club that organises trials and vintage bike rallies and runs and the 'owners section' was just a small part of it. When Sunbeam production ended BSA sold the remaining stock of parts to Stewart Engineering. Bob and Chines Stewart were long time fans of the Sunbeam and for a time members of the Sunbeam Motorcycle Club. In 1963 they, along with other enthusiasts, broke away from the Sunbeam Motorcycle Club and formed the Sunbeam Owners Fellowship (SOF) to support owners of an S7 or S8 with any problems. A good number of Sunbeams motorcycles survive in perfect working order and many owners have been fellows of the SOF since its inception, having owned their Sunbeam since bought new or second hand in the 1960’s.

Dave Burton
www.bargain-motors.com