AJS Model 31 650 CSR Hurricane

Make Model.	AJS Model 31 650
Year	1957 - 66
Engine	Four stroke, pushrod parallel twin, OHV, 2 valves per cylinder,
Capacity	646 cc / 39.4 cu in
Bore x Stroke	72 x 79.3 mm
Compression Ratio	7.5 : 1
Cooling System	Air cooled
Induction	Carburetor
Ignition	6 V (After 1964 12 V) Magnet (Lucas K2F)
Starting	Kick
Clutch	Multi Plate (dry, Burman)
Max Power	31,4 kW / 43 hp @ 6000 rpm
Transmission	4 Speed
Final Drive	Chain
Frame	Single cradle
Front Suspension	Hydraulic telescopic fork
Rear Suspension	Dual chocks
Front Brakes	Drum
Rear Brakes	Drum
Wheels	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).