The AJS Model 31 was a British motorcycle made by Associated Motor Cycles at the former Matchless works in

Plumstead Plumstead is an area in southeast London, within the Royal Borough of Greenwich, England. It is located east of Woolwich. History Until 1965, Plumstead was in the historic counties of England, historic county of Kent and the detail of mu ...

, London. Developed in 1958 specifically to capture the potentially lucrative US market, the last Model 31 was produced in 1966.

Development

AJS Model 31

The AJS Model 31 was also produced as the Matchless G12 by the same company. Designed by Phil Walker, AMC knew that it had to be a 650cc but wanted to use as many cycle parts as possible from the preceding 600cc Matchless G11, which had been

badge-engineered In the automotive industry, rebadging is a form of market segmentation used by automobile manufacturers around the world. To allow for product differentiation without designing or engineering a new model or brand (at high cost or risk), a manu ...

as the AJS Model 30. The cylinders could not be bored out further, so the stroke was lengthened from 72.8mm to 79.3mm, increasing capacity to 646cc. That meant developing a new crankshaft and primary chaincase, which also provided the opportunity to add a

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alternator. Volume production began in September 1958.

AJS Model 31 De Luxe

In 1959 the Model 31 was redesigned and modernised as the ''De Luxe'', with a new full cradle tubular duplex frame and a new cylinder head. Vibration had always been a problem, so the crankshaft was upgraded to nodular iron. Capable of 100 mph performance, the AJS Model 31 became popular with the North American market.

AJS Model 31 CSR

The AJS Model 31 ''CSR'' designation officially stood for ''Competition / Springer / Road'' but it was dubbed the ''Coffee Shop Racer'' by its rivals. With its distinctive two into one "siamese" exhaust system and upgraded camshafts, the CSR was a high-performance motorcycle but still prone to leaks and vibration. The factory diverted Chief Engineer Jack Williams from

AJS 7R The AJS 7R was a British 350 cc racing motorcycle built from 1948 to 1963 by Associated Motor Cycles. It was also commonly known as the ‘Boy Racer’, and won victories both for the factory and for privateers right from its introduction i ...

development to address the problems and modify the bikes for racing, with the result that Ron Langston and Don Chapman won the prestigious Thruxton 500 long distance endurance race on the AJS Model 31. Encouraged by this victory in 1963, AJS named the Model 31 "Hurricane". By 1966 AMC was in financial trouble, and production ended.

References

External links