Matchless G12 & AJS Model 31 

Two great 650cc parallel twins from Plumstead, London


1962 650cc Matchless G12. Full width hubs. Megaphones. AMC forks and AMC gearbox. Durable. Tough. And long-legged. But doesn't quite compare with Triumphs, BSA or Nortons of the era. Or does it? Make sure you don't repeat this assertion if you're talking to a Matchless or Ajay owner who's clutching anything sharp. Or blunt.



Matchless G11 Specifications:


Model year: 1957
Engine: 600cc (593cc) air-cooled parallel twin
Bore & Stroke: 72mm x 72.8mm
Compression ratio: 7.5:1

Power: 33hp @ 6,800 rpm
Lubrication system: Dry sump
Oil capacity: 4.3 pints (imperial)
Carburettor: Single Amal 376 or 378
Ignition: Lucas K2F magneto
Battery: Lucas 6-volt, 12 amp-hours

Primary drive: chain
Clutch: Wet multi-plate
Gearbox: 4-speed (AMC 'box)

Final drive: Chain
Frame: Twin cradle
Front fork: AMC Teledraulic
Rear suspension: Swinging arm, twin shocks/dampers
Front brake: 8-inch SLS drum
Rear brake: 7-inch SLS drum
Front wheel: 3.25" X 19-inch
Rear wheel: 3.50" X 19-inch
Wheelbase: 55-inches

Fuel capacity: 3.7 gallons
Weight: 400lbs

Top speed: 85 - 90mph




1959 AJS Model 31. Same bike as the Matchless G12, but different livery and badge



Matchless G12 (all models)
Model year: 1958 - 1966
Engine: 646cc air-cooled parallel twin
Bore x stroke: 72mm x 79.3mm
Compression ratio: 7.5:1 (8.5:1 CS/CSR)

Power: 35hp @ 6,500rpm
Lubrication system: Dry sump
Oil capacity: 4.3 pints
Carburettor: Amal 389, 1-1/8th inch choke
Ignition: Lucas K2F magneto
6-volt, 12Ah
Primary drive: chain
Clutch: Wet multiplate (AMC 'box)
Gearbox: 4- speed
Final drive: Chain
Frame: Twin cradle
Front fork: AMC Teledraulic
Rear suspension: Swinging arm, twin Girling shocks/dampers
Front brake: 7-inch SLS
Rear brake: 7-inch SLS
Front wheel: 3.25 x 19 inch
Rear wheel: 3.50 x 19 inch
Weight: 396lbs
Fuel capacity: 3.7 gallons
Top speed: 95mph



Think Matchless, think AJS. And vice versa. That's how it was in the 1930s onward when these two well-established and very proud British motorcycle marques were joined at the hip, commercially speaking, and became virtually indistinguishable by the general motorcycling public—except of course by their respective livery and the badges on the fuel tanks.

AJS was founded by the Stevens family in 1909; namely father Joe Stevens, and sons Harry, George, Albert John, and Joe Jnr. It was Albert John Stevens (always referred to as "Jack") whose initials formed the name and logo of the firm.

This inventive company was always very forward looking, technically ingenious and commercially dynamic. The Stevens family manufactured not only motorcycles, but subsequently diversified into numerous other automotive products including cars, car bodies, buses, and coaches. They also contested various Isle of Man TT races and achieved numerous race wins across Europe and beyond.

However, despite their huge expansion, design sophistication and commercial ambition—or, actually, because of it—the company went bust in 1931. BSA, notably, made a play for the AJS assets, but failed. Rival Matchless Motorcycles, owned and founded in 1899 by Henry Herbert Collier and his sons, Charlie and Harry—were more successful and snapped up those parts of the company that fitted their own needs and ambitions; notably the motorcycle assets.


As a result, Amalgamated Motor Cycles was formed six years later in 1937. The following year (1938) that company became Associated Motor Cycles (AMC). The old AJS works in Retreat Street, Wolverhampton was abandoned. All motorcycle production was shifted to the Matchless Works in Plumstead, South London. And by degrees, manufacturing and product design was homogenised leading to near identical bikes being built and badged, respectively, as AJS and Matchless.

It was a black era for hardcore fans of both marques. But industrial competition being what it is, and with the depressed years of the 1930s unfolding, it was inevitable that substantial product merging in all manufacturing sectors was going to happen. And of course, much the same thing followed in later years with BSA and Triumph closing the gap between the two marques and producing similar machines for their core fan base.


Triumph 5T Speed Twin


In 1938 something new and radical shook the foundations of the motorcycle world, and that was Edward Turner's seminal 1938 5T Triumph Speed Twin. This 500cc parallel/vertical twin wasn't the world's first, and it wasn't the first for Triumph either. Val Page's (unglamorous, but technically sound) Model 6/1 designed in 1933 proved the concept, and that motorcycle no doubt gave Turner the impetus needed to revise the design into something ... well, sexier. And it was the Speed Twin that emerged from that commercial crucible and promptly began banging in the coffin nails of the Great British Single which up to that point had been the staple diet of the average British motorcyclist.

WW2, however, came along pretty much at that moment (1939), and it wasn't until after the conflict ended that the 5T Speed Twin project was restarted. The other manufacturers, now also re-committed to manufacturing bikes instead of bombs and bullets, hitched a ride on the same parallel twin wave that was washing away the old single-cylinder orthodoxies. Soon enough BSA was developing its 500cc A7 (1946). Norton was urgently developing the 500cc Model 7 Dominator (1947), and AMC was hard at work readying its new 66 x 72.8mm 500cc Matchless G9/AJS Model 20.

Arguably, none of these contenders matched the elegance and pizzazz of Triumph's 500cc Speed Twin; a bike that was soon enlarged to create the redoubtable 650cc 6T Thunderbird which powered Triumph well into the 1960s and kept the firm way ahead of the pack, saleswise.

But all three rival machines were in their own way creditable debuts and gave new momentum to an industry that was feeling the pinch from the car manufacturers which were relentlessly mopping up erstwhile motorcycle customers and turning them into happy motorists.



Matchless G9/AJS Model 20


The 500cc (actually 498cc) G9/Model 20 joined the half-litre parade in 1948 with a 66mm x 72.8mm parallel twin engine housed in a twin cradle frame with a Teledraulic front fork and swinging arm rear suspension ("upgraded" in 1951 to the famous Jampot shocks). It was a typically conservative, but solid-looking US-focussed roadster that distinguished itself from the competition in one very significant manner.

The G9/Model 20 was mechanically underpinned by a large one-piece cast-iron crankshaft. Conventional roller bearings on either side supported and located this component, and these rollers were backed by a thin-walled Vandervell shell bearing in the centre. Triumph's Edward Turner would probably not have approved. Turner was said to be in favour of "whippier" cranks to help dispel primary and even secondary vibrations. But the AMC designers pressed on with their own ideas, and many (if not most) Matchless/AJS parallel twin riders will tell you that the concept works fine for them. Regardless, that centre bearing was required fitment by AMC thereby giving extra support to the cast iron crank (as opposed to a more expensive steel crank).



1954 Matchless G9. Full width hubs. Megaph



Unusually, the cast iron cylinder barrels, left and right, were separate items that could be independently removed. Ditto the aluminium cylinder heads. Lubrication was handled by a durable twin pump design, each pump driven camshafts fore and aft of the cylinder barrels. These pumps forced a more-than--adequate amount of oil through drillings to the bearings where splash-and-mist lubrication kept the bores and pistons cool and mechanically supple. The rods and piston were, of course, also aluminium.

The camshafts, dynamo and magneto were gear driven. That magneto, in 1952, shifted from the rear of the engine (beneath the carburettor) to the front (beneath the header pipes). AJS left the mag where it was. A single Amal carburettor (which became a Monobloc in 1955) handled the induction. The gearbox was originally a 4-speed Burman design, but by 1956 everything across the range switched to the AMC 4-speed unit which was a development of pre-war Norton 'boxes that in turn came from Sturmey-Archer.



1954 Matchless G9/AJS Model 20. 500cc. Pressed steel (and often leaky) primary chaincase. Launched in 1948, this updated engine was AMC's answer to Edward Turner's 500cc 5T Speed Twin. It was a worthy design and helped restore the pride of Matchless and AJS men looking to ride with the ever faster pack from Meriden, Bracebridge Street and Small Heath. But the model never saw the same success in the showroom.



1954 Matchless G9 pilot lights. For 4 years AMC lit these up, then quietly dropped them. Why? Just dated looks perhaps in an age where most riders were thinking sporty thoughts.



Matchless distinguished its 500 from the AJS, notably by the respective logos cast into the timing cover, but also in other respects. Matchless, for instance, favoured a dual seat and megaphone silencers, while AJS opted for a more traditional sprung saddle/pillion pad plus tubular silencers. For 1954, twin pilot lights appeared and graced either side of the headlamp. These lights lasted until 1958 when alternator electrics arrived.

Wheels were 19-inchers. The all-up weight was around 400lbs. The bike was good enough for around 85mph; perhaps a little faster under the most favourable conditions. Overall, these were solidly planted machines that returned average fuel economy (around 55mpg), handled competently (if not excitingly), enjoyed barely-adequate-to-marginal braking, and good all round reliability.

But they vibrated more (or at least differently) than, say, the rival Speed Twin. So okay, if you understood your bike and kept your revs under control, you could dial out the worst of the tremors. However, AMC's customers couldn't go on forever pretending that they liked riding at exactly this-or-that speed in an effort to smooth out the worst of it, so up upgrade was required.

Not that the vibes were so bad as to totally wreck a rider's enjoyment. Indeed, many riders would tell you the opposite; that the few vibrations there were didn't amount to anything you wouldn't experience on other marques. Nevertheless, AMC felt that it was time to roll out the enlarged 600cc Matchless G11/AJS Model 30.



Matchless G11/AJS Model 30


In 1955, the 600cc Matchless G11/AJS Model 30 (image immediately above) was unveiled; a bike (or pair of bikes) that helped bridge the gap between the 500s and the 650s, the latter being the new magic numbers for the performance oriented buying public of the day—notably in the USA which was buying pretty much all the motorcycle hardware that Britain could throw in that direction.

The Matchless G11/AJS Model 30 was, however, a short-lived concept. After just just four years (1955 - 1958) it was superseded by the 650cc G12/AJS Model 31 (although for one year the 600s and the 650s were both available as new.




Matchless G12/AJS Model 31


From the start, the Matchless G12/AJS Model 31 was a solidly built, reliable, if slightly dowdy motorcycle. Much understanding had been gained by AMC regarding the fortitude and foibles of the G11/Model 30. But taking that 600cc engine out to 650cc required some re-jigging, not least with regard to the cylinder barrels, stroke and crank.

Put simply, there wasn't sufficient meat on the bone to overbore the 72mm x 72.8mm G11/Model 30. So the answer was to increase the stroke to 79.3mm. That required a different crank throw. And because vibration was still something of a bugbear (especially on these more powerful engines) and was known to snap the cast iron cranks, AMC upgraded to a nodular iron crankshaft.



The metallurgy here was notably different inasmuch as the new nodular material contained more free carbon/graphite thereby creating ductile iron. The graphite within ductile iron is spherical, as opposed to flaky graphite in ordinary cast iron, and that spherical nature helps distribute forces more fluidly instead of concentrating stresses on the graphite flake edges. The result? A crank less prone to snapping.

That same year saw the introduction of the G12 De Luxe which was wrapped tightly in a full twin cradle frame (as opposed to two cradles beneath the engine supported by a single down tube). Straight line performance was nudging 100mph, but few riders would want to stay up there for very long. The G12 was best enjoyed at 55 - 65mph with occasional blasts up to 75 or even 80mph.



The CS (Competition/Sprung) version came next (image immediately above) and was from the start aimed at the US desert racing scene where Triumph and BSA were helping set the pace; hence the fact that it was marketed in America as the Apache (and as the Monarch in the UK). The Matchless was certainly a worthy opponent being tough and reliable, but it (arguably) lacked the eye appeal of other contenders, and it sold in smaller number.

One of the most distinguishing features on this bike was the siamese 2-in-1 exhaust system, and it backed this more racy look with 8.5:1 high compression cylinders (up from 7.5:1 on the standard G12), big valves, competition heads, and revised camshafts.

The tank was smaller. Alloy mudguards and QD (quickly detachable) lights were fitted. The tyres were slightly fatter.

Then came the CSR (Competition/Sprung/Roadster) model, aka "Coffee Shop Racer" which boasted much the same features but with a standard fuel tank for increased practicality on the road.



This bike could top the top and his around 105mph. The clutch action, when suitably fettled, is about par for the course for a British parallel twin of the era. Suspension is good, but not superlative. Braking is never more than barely acceptable. General comfort and ergonomics leave little to complain about. The engine pulls assuredly with plenty of surge in the mid-range.

General fast-moving and maintenance spares for these motorcycles, largely thanks to the AJS & Matchless Owners Club, are not too difficult to source. But as ever, original tinware is hard to find.

We searched eBay and found these G12 racing manifolds for sale at £130 (image immediately above, December 2019 prices). A set of Indian-made repro mudguards in raw steel was on offer at £190. A G12 CSR fuel tank was asking £202. A pair of second hand cylinder heads were being offered at an £18 start price. A pair of second hand oil pumps were priced at £89.

As ever, with repro parts you should ask very searching question about manufacturing quality and dimensional precision, etc.





Cheffins auction house sold the above box of Matchless G12 parts in 2016 for just £50. So seek and you will find. It's all out there somewhere.









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