Sunbeam S8

Designed as Britain's answer to the BMW, the Sunbeam S7 and later the S8 were odd mixtures of the inspired and the impractical, which was ultimately to condemn them to being an interesting backwater, rather than part of the mainstream of post-war motorcycling.

Several influences were at work but the new machines were BSAs in all but name. Sunbeam had ceased to be a truly separate entity during the 1930s and the trademarks now belonged to the giant BSA organisation, which reasoned that they could capitalise on Sunbeam's gentlemans motorcycle image for their new tourer.

The design was the work of independant designed Erling Poppe but was heavily based on the BMW R75, manufacturing rights to which had been offered to BSA as part of the war reparations. But while the double-cradle frame and telescopic fork echoed the BMW, the engine was a completely new design. Displacing 487cc, the engine was basically a parallel twin not unlike that offered by the BSA A7, but it was housed in alloy casings and turned around so that the crankshaft ran in line with the frame.

The first of the Sunbeam's problems arose from the choice of transmission. The intention was to use a shaft drive like the BMW but the design adopted had a worm gear in place of the German machine's bevels. While easier to manufacture, it was inherently weak and on prototypes the worm stripped its thread if the engine was fully used. The second problem was vibration. This had been evident on the prototypes but the signs were ignored until the bike went into production in 1946. When an initial batch was despatched to a police team intended to escort King George VI, it was reported that they were unridable.

The bike weighed more than 400lb - but looked heavier. Fitted with 16in balloon tyres, its handling was prone to vaguenessm which became aggravated as the plunger rear suspension units wore. The finish, in BSA's rather drab mist green, can hardly have helped its showroom appeal, any more than the stories of its mechanical defects, and it was a poor seller.

In 1949 BSA decided to tackle both the performance and the styling by launching the new S8 as a sports alternative to the touring S7. Lighter than its predecessor, this used cycle parts such as forks and wheels from other BSA models. It was a more popular bike than the S7 but was still no runaway success. BSA finally discontinued the Sunbeams in 1956.

Sunbeam S8

• Years in production - 1946-56
• Engine type - parallel twin (in-line) overhead-cam four-stroke
• Bore and Stroke - 70 x 63.5mm
• Capacity - 487cc
• Power - 24bhp @ 6000rpm
• Carburettor - Amal
• Tyres - 4.75 x 16in
• Wheelbase - 57in
• Weight - 430lb (S7), 413lb (S8)