When announced in 1948, AMC's new twin-cylinder models, the AJS Model 20 and equivalent Matchless G9, while following the established pattern of British parallel twins, were unusual in having an engine with a third, central, crankshaft main bearing. Progressively developed, the motor underwent a number of capacity increases from the original 498cc, finally arriving at 646cc in the autumn of 1958 with the launch of the AJS Model 31 and Matchless G12. The new range-topping super sports models were typed 'CSR'. Production ceased in 1966. Not first registered until 1968, this Model 31SCR was acquired by the current vendor in 1978 and has been off the road for many years. Offered for restoration, the machine comes with the purchase receipt, an expired MoT (1980) and an old-style V5 document.