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AJS Model 31 & Matchless G12



AMC | AJS | Matchless | CS | CSR | Review | Jampot


AJS Model 31 650cc


▲ 1966 AJS Model 31. Bonhams sold this example in 2010 for £2,875. Since then, typical selling prices for this model (and the identical AMC stablemate, the Matchless G12), rose steadily to around £4,750, but have since stagnated. Up to £6,000 asking price has been fairly common. Owners buy these twins for their solidity and surefootedness, but never for their sex appeal. Tip: get a top box and panniers and go touring. The AJS Model 31/Matchless G12 will carry you effortlessly for hundreds or thousands of not-too-exciting miles.




We've ridden a few of these classic AMC twins, and it's always a pleasant surprise to rediscover how smooth they can be. Not that they don't vibrate. They do, but you have to ride them pretty hard to rattle any fillings. And if you do experience anything beyond that, you know that something's gone haywire in the crankcase.


AJS Motorcycle brochure 1956 - 1957They're planted like oak trees. The ride is always satisfactory, but without offering anything too dramatic. Bends are taken smoothly and, generally, minus the twitchiness you sometimes get from other marques (Triumph owners, sit down). The Teledraulic fork needs to be set up carefully and tuned to suit personal tastes (i.e. experiment with fork oil weight and/or fit progressive fork springs). Clutches should be reasonably light. The AMC gearbox selects positively. The exhaust note is fairly muted but not exactly dull. The 7-inch brakes are pretty weak and need to be kept in fine fettle for use on modern roads.


As of 2019, these 650cc parallel twins have to a great extent fallen out of fashion. Yes, there's still an interest. But the demand is lower than it was. Consequently, they can take a while to fetch their typical asking price if pegged at around £5k. Yes, we still see examples offered at over £6k, but it's not clear how many actually sell at that price—and note that many owners of these bikes, as with other marques, refuse to sell them "cheap". So stagnation sets in.


Matchless G12 engine schematic


▲ Matchless G12 engine schematic. If you want to describe these engines in a single word, try "robust". The AMC engineers followed sound mechanical principals and didn't take too many chances. Left and right side barrels and cylinder heads remove separately. A twin oil pump driven by the camshaft supplies oil at pressure through drillings to the crankshaft.



If you're planning to ride any significant miles, we'd recommend upgrading to 12-volts, fitting a high power alternator and maybe even very discreet indicators if you're riding on a daily basis. Upkeep is not too tricky. All the problems/foibles are known, and fixes are available. Keeping these bikes clean is reasonably straightforward.


Spares are very good for these, incidentally. Talk to the AJS & Matchless Owners Club. These guys and girls have pretty much got it all figured out and produce a range of good quality parts for many models.


Tip: If you want one with a few extra thrills, check out the CS (Competition/Sport) and CSR (Competition/Sport/Road) models.


Finally, check our more comprehensive AJS Model 31/Matchless G12 buyers guide.




1966 AJS Model 31 specifications



Engine type: Air-cooled, OHV parallel twin

Displacement: 646cc
Power: 35hp @ 6,500 RPM
Compression: 7.5:1
Bore x stroke: 72mm x 79.3mm
Fuel system: Single 1-1/8th Amal 389 carburettor

Lubrication: Dry sump
Ignition: Lucas K2F magneto

Electrics: Lucas 6-volt, 12aH, alternator

Clutch: Wet multiplate
Gearbox: 4-speed

Primary drive: Single row chain
Final drive: Chain
Fuel capacity: 3.7 gallons (imperial)
Frame: Twin cradle
Front suspension: AMC Teledraulic telescopic fork
Rear suspension: Twin Girling shock absorbers/dampers
Front tyre: 3.25-19-inch
Rear tyre: 3.50-19-inch
Front brakes: 7-inch SLS drum
Rear brake: 7-inch SLS drum
Dry weight: 388lb (176kg)

Top speed: 90 - 95mph




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