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.
- Years in production - 1946-56
- Engine type - parallel twin (in-line) overhead-cam
- 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)