BSA B31 Parts & Spares
The 348cc B31 was BSA’s post-war overhead-valve 350 single, a straightforward, well-built machine that sold in large numbers and is still a sensible first classic. Its 500cc sister, the B33, uses much of the same design, which helps when you are hunting for parts. Many were used hard as daily transport, so a B31 on the bench today has often seen more than one rebuild.
Obsolete Bike Parts holds B31 engine, gearbox and cycle parts, in original and NOS form where we can source it and in reproduction where we cannot. We send parts worldwide from the Netherlands.
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€ 44,00 Select options This product has multiple variants. The options may be chosen on the product page -
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€ 46,00 Select options This product has multiple variants. The options may be chosen on the product page
Rigid, plunger or swinging arm?
Over its production life the B31 was built with a rigid rear end, then with plunger rear suspension, and finally in a swinging-arm frame. Frame, rear wheel, mudguard and fitting parts change with each of those. The engine stayed close to the B33 throughout, but bore-related parts are specific to the 350. Front forks, brakes and electrics were also revised over the years, and parts from a B32 or B34 competition model may have found their way onto a road bike. The numbers settle what the machine started out as.
B31 parts we keep
- Engine: 350 pistons and rings, valves, guides and gasket sets
- Gearbox and primary: clutch parts, gearbox components, chains
- Electrics: Lucas magneto, dynamo and lighting parts
- Cycle parts: fork, brake and control components, cables and fasteners
- Carburation: Amal service parts for the carburettors used on the B31
Check before you buy
A quick look at your frame and engine numbers tells us which frame type and year range we are dealing with. Send them over with your question and a note on what the bike is being built for.