AJS Model 31 650 CSR Hurricane



Make Model.

AJS Model 31 650


1957 - 66


Four stroke, pushrod parallel twin, OHV, 2 valves per cylinder,


646 cc / 39.4 cu in
Bore x Stroke 72 x 79.3 mm
Compression Ratio 7.5 : 1
Cooling System Air cooled




6 V (After 1964 12 V)  Magnet (Lucas K2F) 


Clutch Multi Plate (dry, Burman)

Max Power

31,4 kW / 43 hp @ 6000 rpm


4 Speed

Final Drive

Frame Single cradle

Front Suspension

Hydraulic telescopic fork

Rear Suspension

Dual chocks

Front Brakes


Rear Brakes



Steel, wire spokes

Front Tyre

3.25 -19

Rear Tyre

3.50 -19

Dry Weight

176 kg / 388 lbs

Fuel Capacity 

16 L / 4.2 US gal


The models:

AJS Model 31
The AJS Model 31 was also produced as the Matchless G12 by the same company. Designer by Phil Walker, AMC knew that it had to be a 650cc but wanted to use as many cycle parts from the Model 11 as possible. The cylinders could not be bored out further so the stroke was lengthened from 72.8mm to 79.3mm, resulting in a capacity of 646cc. The meant developing a new crankshaft and primary chaincase, which also provided the opportunity to add a Lucas 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.[1] Capable of 100 mph performance, the AJS Model 31 became popular with the American market.

AJS Model 31 CSR

The AJS Model 31 CSR designation officially stood for Competition / Sport / Road but it was dubbed the Coffee Shop Racer by its rivals. With its distinctive 2 into 1 '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 the AJS Model 31 gained the name Hurricane).