Matchless G12

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Matchless G12
Manufacturer Associated Motorcycles Plumstead, London
Also called 'Monarch'
Production 1958 - 1966
Predecessor Matchless G11
Engine 646 cc (39 cu in) air cooled twin
Power 35 bhp (26 kW) @ 6,500rpm
Transmission Four speed gearbox to chain final drive
Brakes drum brakes
Weight 396 pounds (180 kg) (dry)

The Matchless G12 was a British motorcycle made by Associated Motorcycles at the former Matchless works in Plumstead, London. Developed in 1958 specifically to capture the potentially lucrative US market, the last G12 was produced in 1966.


Matchless G12

The Matchless G12 was one of the last motorcycles under the Matchless name and was also produced as the AJS Model 31 by the same company.Designer by Phil Walker, AMC knew that it had to be a 650 cc (40 cu in) 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 72.8–79.3 mm (2.87–3.12 in), resulting in a capacity of 646 cc (39 cu in). This meant developing a new crankshaft and primary chaincase, which also provided the opportunity to add a Lucas alternator. Volume production began in September 1958.

Matchless G12 De Luxe

In 1959 the G12 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. ]] (My 1960 G12CSR did not have a nodular crankshaft and broke to prove it, the factory did fit a replacement nodular iron crankshaft free of charge; if you tap the crankshaft and it rings it is not nodular iron, if it just goes 'thud' it is). Capable of 100 mph (160 km/h) performance, the G12 became popular with the American market.

Matchless G12 CS

The Matchless G12 CS (sometimes referred to as the CS X) was an off-road version of the Matchless G12 with improved ground clearance and a slightly upswept exhaust. It was not a trials competition machine but instead aimed at the 'desert racer' market in the US.

Matchless G12 CSR

The Matchless G12 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 version of the G12. Encouraged by this victory in 1963 the G12 CSR gained the name Monarch and twin carburettors (the AJS version was renamed the Hurricane).

Matchless G15/45

In 1964 the CSR gained Norton brakes and forks, and the following year a Norton Atlas 750 cc (46 cu in) engine replaced the trouble prone AMC unit. In 1962 and 1963, AMC had produced a limited run of 212 touring motorcycles of 738cc displacement using an enlarged version of the G12 AMC-designed engine, but these bikes - which were given the model designation "G15/45" - proved even less reliable than the 650 cc (40 cu in) version when ridden hard. So AMC's original plans to develop a 750 cc (46 cu in) desert racer version were abandoned. If successful, this could have saved the company as there was a huge unmet demand in the US for powerful desert racers to compete in endurance events. By this time the company were in financial trouble and production ended in 1966.

This article uses material from the Wikipedia article Matchless G12,
which is released under the Creative Commons Attribution-Share-Alike License 3.0.

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