| 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 BSA B50 is a motorcycle made by BSA at their factory in Small Heath, Birmingham. The last of the big capacity unit singles from the Birmingham Small Arms company, it had a 499 cc alloy engine with a bore of 84 mm (3.3 in) and a stroke of 90 mm (3.5 in), a short wheelbase and unusually high centre of gravity. As well as the road going version, special models were produced for off road competition use[1].
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The B50 included many new features such as oil in the Frame technology and the electrics in a single removable 'pod' - ideas that were quickly picked up by the Japanese competition[2]. BSA needed to keep production costs down and made use of as many existing factory parts as possible, such as the unit single crankcases from the older 250cc engine. This meant that the B50 required very careful assembly of crankcase and rocker box gaskets and seals to avoid oil leaks. The extra torque of the B50 also led to slipping of the standard BSA clutch and riders often modified it by adding an extra friction plate and stronger clutch springs. The ignition coils used on many production B50 models were also salvaged parts and led to difficulty starting and erratic slow running[1].
About 5,700 were built,[1] but few survive in original condition as many were modified for off road use by specialist builders such as Eric Cheney[3].
B50 bikes were successful in both road-racing and off-road events. In particular, a modified B50 Gold Star 500 entered by Mead & Tomkinson of Hereford England and ridden by Nigel Rollason and Clive Brown won the 500 cc 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 TT.[4][5]
After the demise of BSA, Alan Clews bought up remaining B50 part stocks and set up Clews Competition Motorcycles, producing successful scramblers based on the B50.
The BSA B50 SS 'street scrambler' was designed for on-road use and was aimed at the US export market and proved its credentials by winning the 500cc class in the Thruxton 500 miler and the Barcelona 24 hour endurance race[2].
Trail version
The B50 MX was designed for off road competition and produced between 1971 and 1973[1]. 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[6].
Specialist motorcycle designer Gerald Fitzpatrick created a 1,000 cc BSA V-twin using two B50 engines in 1977. The frame was a slimline featherbed Norton Atlas. Triumph considered putting the B100 into production but were not able to finance re-tooling costs[7].
The B100 prototype was ridden for two years has stored since but was featured in the magazine British Bike Mechanics in April 1978 and January 1988[7].