BSA
B31
The BSA B31, introduced in 1945, was the first
new model introduced by the company after the
Second World War. Based on pre-war designs,
it used a single cylinder four stroke engine
that displaced 348 cc (21.2 cu in). Initially,
it had a rigid frame and telescopic forks, the
first use of such on a BSA. It developed about
17 bhp (13 kW), adequate for the roads of the
day and enough to deliver a top speed of around
70 mph (110 km/h). It was immediately popular
and was soon joined by a 500 cc (31 cu in) version,
the BSA B33 and competition equivalents, the
BSA B32 and BSA B34.
Plunger rear suspension was offered later,
with a swingarm rear suspension frame available
from 1954. The model continued in production
until 1959, by which time the traditional Lucas
magdyno had been replaced by an alternator and
coil ignition.
The B series expanded through its life to
include the famous BSA Gold Stars, and the bottom
half of all engines has much in common with
the M series side valve models. The M33, designed
for sidecar work, combined the strong M series
frame and the better performing B33 500 cc overhead
valve engine.
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