500 cc (31 cu in) 654 cc (39.9 cu in) 751 cc (45.8 cu in) air-cooled OHV twin
Bore / stroke
500: 65.5 mm × 74 mm (2.58 in × 2.91 in) 650: 75 mm × 74 mm (3.0 in × 2.9 in) 750: 75 mm × 85 mm (3.0 in × 3.3 in)
Ignition type
Twin coil
Transmission
Triplex primary chain, 4 speed gearbox
Frame type
Half-duplex cradle
Brakes
7"/8" drum front 7" drum rear 8" 2ls drum 1968 on
Wheelbase
54 in (1,400 mm)
Turning radius
14 ft (4.3 m)
The BSA unit twins were a range of unit construction twin-cylinder motorcycles made by the Birmingham Small Arms Company (BSA) and aimed at the US market. A range of 500 cc (31 cu in), 650 cc (40 cu in) and 750 cc (46 cu in) twins were produced between 1962 and 1972,[1] but they were really developments of the older pre-unit A7/A10 model range with less weight.[2] The engines had a reputation for vibration, but acceleration was good for the time, to a top speed of 100 miles per hour (160 km/h).[1]
Models for the US generally had smaller petrol tanks and higher wider handlebars than the UK models, and prior to 1966 different model names were used for the two markets.
The 500cc models were discontinued in 1971 when the single cylinder B50 model was introduced.
The BSA Group faced worsening financial difficulties and in 1973 merged with Norton-Villiers. As part of a rationalisation by the newly formed Norton Villiers Triumph, production of BSA motorcycles ceased.
^ abKemp, Andrew; De Cet (2004). Classic British Bikes. Mirco. Bookmart Ltd. ISBN 978-1-86147-136-9.
^Bacon, Roy (1988). British Motorcycles of the 60's. Osprey Publishing. ISBN 978-1-85648-166-3.
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