AJS Model 31 CSR
Year:
1959
Manufacturer:
Associated Motor Cycles, Plumstead, London.
Number Produced:
Unknown
Specifications:
646cc parallel twin OHV 4 stroke engine
Top speed approx. 100 mph (160 km/h)
4 speed gearbox
Description:
Introduced in the mid-1950s, the Model 31 was AJS’s 650cc twin and shared its mechanical design with the Matchless G12, both produced by Associated Motor Cycles (AMC).
The CSR version - standing for Competition / Sport / Road - was the high-performance variant. It featured twin carburettors, uprated camshafts and sportier tuning, offering strong performance for its day. Rival manufacturers jokingly dubbed it a “Coffee Shop Racer,” reflecting its appeal to performance-minded riders.
Some models were fitted with a distinctive 2-into-1 “Siamese” exhaust system, although twin exhausts were also common depending on year and specification.
Competition-prepared versions of the Model 31 achieved success in endurance racing, including victory at the prestigious Thruxton 500 in the early 1960s - an important promotional triumph for AJS.
By the mid-1960s, AMC was experiencing financial difficulties. Production of the AJS heavyweight twins, including the Model 31 CSR, ended around 1966.
