Sunbeam S7 and S8
Encyclopedia
The Sunbeam S7 and S8 are British motorcycle
s designed by Erling Poppe based on the BMW R75
designs that were acquired by BSA
(together with the full rights to the Sunbeam
brand) at the end of World War II
.
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. 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 De Luxe and the S8, which were produced with fewer 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 "de luxe" 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 de luxe (5,554 produced) and the S8 (8,530 produced). Both had new cylinder linings, redesigned frames and increased oil capacity. The S8 was sold as a "sports" model with increased performance from higher compression pistons with a top speed of 85 mi/h. It also had new forks, a cast aluminum 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.
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 undampened front fork system which affected handling. There were also trials with a rigid version for a cheaper model but this design was also abandoned.
Some early models of the original S7 were produced in black but most in the now familiar "Mist Green". The S7 de luxe came in either "Mist Green" or black and for export abroad BSA supplied Sunbeams in any colour.
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 1960s.
A web-based owners club has been created .
Motorcycle
A motorcycle is a single-track, two-wheeled motor vehicle. Motorcycles vary considerably depending on the task for which they are designed, such as long distance travel, navigating congested urban traffic, cruising, sport and racing, or off-road conditions.Motorcycles are one of the most...
s designed by Erling Poppe based on the BMW R75
BMW R75
The BMW R75 is a World War II-era motorcycle and sidecar combination produced by the German company BMW.In the 1930s BMW were producing a number of popular and highly effective motorcycles...
designs that were acquired by BSA
BSA
-Organizations:* Baltimore School for the Arts* Bank Secrecy Act* Bearing Specialists Association* Belarusian Socialist Assembly* Bhutan Scouts Association* Bibliographical Society of America* Birmingham School of Acting...
(together with the full rights to the Sunbeam
Sunbeam (motorcycle)
Sunbeam was a British manufacturing marque that produced bicycles and motorcycles from 1912 to 1956. Originally independent, it was ultimately owned by BSA...
brand) at the end of World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
.
Built in Redditch
Redditch
Redditch is a town and local government district in north-east Worcestershire, England, approximately south of Birmingham. The district had a population of 79,216 in 2005. In the 19th century it became the international centre for the needle and fishing tackle industry...
, 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. 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 De Luxe and the S8, which were produced with fewer features to reduce costs, while retaining many of the innovative parts of the early Sunbeam and updating some ideas.
Models
Three models were produced, the S7, S7 "de luxe" 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 de luxe (5,554 produced) and the S8 (8,530 produced). Both had new cylinder linings, redesigned frames and increased oil capacity. The S8 was sold as a "sports" model with increased performance from higher compression pistons with a top speed of 85 mi/h. It also had new forks, a cast aluminum 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.
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 undampened front fork system which affected handling. There were also trials with a rigid version for a cheaper model but this design was also abandoned.
Some early models of the original S7 were produced in black but most in the now familiar "Mist Green". The S7 de luxe came in either "Mist Green" or black and for export abroad BSA supplied Sunbeams in any colour.
Design problems
Erling Poppe’s design was originally based on a captured BMW R75 but Sunbeam did not 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 Sunbeam 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. BSA had machinery they had inherited from Lanchester Motors to produce worm gears. This created problems with the shaft drive, as the gears tended to strip under power. BMW-style bevel gears would have been superior. Sunbeam's solution to this was to reduce the power to 24 bhp, which did nothing to help post war sales.Owners clubs
A web-based owners club has been created .