The AJS Model 31 was a British

motorcycle A motorcycle (motorbike, bike; uni (if one-wheeled); trike (if three-wheeled); quad (if four-wheeled)) is a lightweight private 1-to-2 passenger personal motor vehicle Steering, steered by a Motorcycle handlebar, handlebar from a saddle-style ...

made by

Associated Motor Cycles Associated Motor Cycles (AMC) was a British motorcycle manufacturer founded by the Collier brothers as a parent company for the Matchless and AJS motorcycle companies. It later absorbed Francis-Barnett, James Cycle Co, James, and Norton Motorcy ...

at the former

Matchless Matchless is one of the oldest marques of British motorcycles, manufactured in Plumstead, London, between 1899 and 1966. A wide range of models were produced under the Matchless name, ranging from small two-strokes to 750 cc Four-stroke cy ...

works in

Plumstead Plumstead is an area in southeast London, within the Royal Borough of Greenwich, England. It is located east of Woolwich. History Plumstead has been settled since ancient times, and London's earliest timber structure has been found here. ...

, 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 (also known as badge engineering, an intentionally ironic misnomer in that little or no actual engineering takes place) is a form of market segmentation used by automobile manufacturers around the world. ...

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

Lucas Lucas or LUCAS may refer to: People * Lucas (surname) * Lucas (given name) Arts and entertainment * Luca Family Singers, or the Lucas, a 19th-century African-American singing group * Lucas, a 1960s Swedish pop group formed by Janne Lucas Perss ...

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 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.

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