Sunbeam S7 and S8
From Wikipedia, the free encyclopedia
| Sunbeam S8 | |
 |
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| Manufacturer |  Sunbeam (BSA) |
|---|---|
| Production | 1946-1956 |
| Engine | 487cc parallel twin OHC four stroke |
| Power | 24 bhp @ 6000 rpm |
| Wheelbase | 57-inch (1,400 mm) |
The Sunbeam S7 and S8 are British motorcycles designed by Erling Poppe based on the BMW R75 designs that were aquired by BSA (together with the full rights to the Sunbeam brand) at the end of World War 2[1] 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 engines on BMW motorcycles had already used shaft drives. Although the early S7 was not a good seller or mechanically very sound, it is the most sought after and commands a premium over the S7 Deluxe and the S8.
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[edit] Models
Three models were produced, the S7, S7 'Deluxe' and the S8. The original S7 (the 'Tourer') was produced from 1946 to 1948 and did not sell well. In 1949 the S7 was updated to become the S7 de-luxe and the S8. Both had new cylinder linings, redesigned frames, increased oil capacity and BSA 'A' series forks to improve handling. The S8 was sold as a ‘sports’ model with increased performance from higher compression pistons with a top speed of 85mph. It also had new forks, a cast aluminium silencer and chromed wheels (with narrower tyres to replace the 'Balloon' tyres which had led to uncertain handling at speed). S9 and S10 models were planned but never made as BSA decided to concentrate on the more traditional twins. [2]Another `sports' model was also tested but never put into production. This had a much higher compression ratio with a different OHC design but was never sold, reputedly because of the undamped front fork system which affected handling. There were also trials with a rigid version for a cheaper model but this design was also abandoned. [3]
The original S7 was available only in black, while the standard colours for the S8 were "Polychromatic Grey" or black. The S7 Deluxe came in either "Mist Green" or black. For export abroad BSA supplied Sunbeams in any colour. [4]
[edit] Design Problems
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 the early models sold had to be recalled to fit rubber engine mounts.[2]
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.[1]
[edit] Owners Clubs
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.[5] 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.
[edit] References
- ^ a b Kemp, Andrew (2001). Classic British Bikes. Bookmart Ltd, pp. 124-125. ISBN 1-86147-058-4.
- ^ a b Shaft Drive Sunbeam Motorcycle History. Retrieved on 2008-06-03.
- ^ A Brief History Of Sunbeams. Stewart Engineering. Retrieved on 2008-06-02.
- ^ Sunbeam S7. Retrieved on 2008-06-02.
- ^ Sunbeam Motorcycle Club. Retrieved on 2008-06-02.
