The BSA B50 was a single-cylinder 499 cc (30.5 cu in) motorcycle, produced by BSA at their factory in Small Heath, Birmingham. The last of the big capacity unit-construction singles from the Birmingham Small Arms company, it had an alloy engine with a bore of 84 mm (3.3 in) and a stroke of 90 mm (3.5 in). As well as the road version, special models were produced for off road competition use.

Manufacturer BSA
Production 1971–1973
Engine 499 cc (30.5 cu in) air cooled, four stroke, OHV unit single
Power 34 hp (25 kW)
Transmission 4-speed, multi-plate wet clutch


The B50 was derived from the earlier 250cc BSA C15/Starfire, and included features such as “oil in the frame” and the electrics in a single removable ‘pod’. BSA kept production costs down by using parts across a range of models, launched in 1971. About 5,700 were built but few survive in original condition. Some were modified for off road use by specialist builders such as Eric Cheney.

Racing success

B50 bikes were successful in both road-racing and off-road events. A modestly-modified B50 Gold Star 500 entered by Mead & Tomkinson of Hereford, England and ridden by Nigel Rollason and Clive Brown won the 500cc class in both the Thruxton 500 miler and the Barcelona 24 hours ( at the Montjuïc circuit), and won the Zolder 24 hour race outright. Also, a B50 fielded by Mead & Tomkinson once held the class lap record in the Production Isle of Man TT.

After the demise of BSA, Alan Clews bought up remaining B50 part stocks and set up Clews Competition Motorcycles, producing successful CCM scramblers (motocross) based on the B50.

B50SS (Street Scrambler)

The BSA B50SS ‘street scrambler’ was designed for road use and was partly aimed at the US market and proved its credentials by winning the 500cc class in the Thruxton 500 miler and the Barcelona 24 hour endurance race.

B50MX (Moto Cross)

The B50MX was designed for off-road competition and produced between 1971 and 1973. The very last MX’s produced were therefore coming off the production line after the demise of BSA and were ‘badged’ as the Triumph TR5MX.

B100 V-Twin (with two B50 cylinders)

Specialist motorcycle designer Gerald Fitzpatrick created a 1000cc BSA V-twin using parts from two B50 engines in 1977. The frame was a slimline feather bed Norton Atlas. Triumph considered putting the B100 into production but were not able to finance re-tooling costs.

The B100 prototype was ridden for two years and has been stored since but was featured in the magazine British Bike Mechanics in April 1978 and January 1988

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