With the constant demand for more power throughout the 1950s, AJS pushed its ever-popular 498-cubic centimeter engines to a whopping 592 cubic centimeters, but even that was not enough. In an effort to capture the North American market, AJS redesigned the bottom end to allow for more stroke, and by late-1958, AJS had a 646-cubic centimeter engine capable of speeds greater than 97 mph.

This Model 31 is currently set up for display purposes only and shows nicely throughout, although it requires much of its electrical wiring. Currently fitted with period-correct saddle bags, these bikes were noted as being very stylish for the time.