AJS Model 31 650 Specs

About the AJS Model 31 650

The AJS Model 31 was the flagship of the AJS twin range, introduced in 1958. Technically, its 646cc engine was a robust and powerful unit, but it was the "CSR" (Competition Sport Road) variant that earned the bike its legendary status. The Model 31 CSR, nicknamed the "Coffee Shop Racer" or "Hurricane," featured a high-compression engine, 2-into-1 exhausts, and a more aggressive stance, making it one of the fastest British bikes of its day. The Model 31 benefitted from a strengthened crankshaft and improved cooling to handle the increased power. It was one of the first AJS machines to utilize the updated "slimline" primary chaincase and improved gearbox. This database provides the technical specifications for the Model 31 range, detailing the horsepower, torque, and dry weight figures. For many enthusiasts, the Model 31 CSR represents the pinnacle of the AMC twins, offering a blend of Italian-inspired styling and British mechanical muscle.