The Matchless G12 was a British 650 cc twin made by Associated Motor Cycles at the former Matchless works in Plumstead, London. Developed in 1958 to capture the American market, it was also sold as the AJS Model 31 and remained in production until 1966.
Matchless G12 at a glance
| Maker | Associated Motor Cycles (Matchless), Plumstead, London |
|---|---|
| Production | 1958–1966 |
| Engine | 646 cc air-cooled four-stroke twin |
| Designer | Phil Walker |
| Stroke | 72.8 mm, lengthened to 79.3 mm from the Model 11 |
| Compression | 7.5:1 standard, 8.5:1 on CS and CSR |
| Top speed | 100 mph (160 km/h) for the De Luxe |
| Frame | full cradle tubular duplex from 1959 |
| AJS equivalent | Model 31 |
| Versions | De Luxe, CS, CSR |
| Production ended | 1966 |
Based on one source: the English Wikipedia article on the Matchless G12.
History of the Matchless G12
A 650 for America
The Matchless G12 was one of the last motorcycles designed under the Matchless name. Phil Walker’s team at Associated Motor Cycles needed a 650 cc twin for the potentially lucrative US market, but the cylinders of the existing 500 cc Model 11 could not be bored out further, so the stroke was lengthened from 72.8 to 79.3 mm. The result was 646 cc, and it required a new crankshaft and primary chaincase — which in turn made room for a Lucas alternator. Volume production began in September 1958, and the same machine was sold as the AJS Model 31.
De Luxe, CS and CSR
In 1959 the G12 was redesigned as the De Luxe with a full cradle tubular duplex frame and a new cylinder head; vibration, always a problem, was addressed with a nodular iron crankshaft. The result could reach 100 mph and became popular in America. The G12 CS was an off-road version with more ground clearance, a slightly upswept exhaust and an 8.5:1 compression ratio, aimed at the desert-racer market rather than trials. The G12 CSR — Competition Sprung Roadster — added a two-into-one siamese exhaust and uprated camshafts, and was nicknamed the Coffee Shop Racer by rivals. Ron Langston and Don Chapman won the Thruxton 500 on the AJS version, and in 1963 the CSR became the Monarch in Britain and the Apache in the US, with twin carburettors.
The end
In 1964 the CSR received Norton brakes and forks, and the following year a Norton Atlas 750 cc engine replaced the AMC unit. AMC had already built 212 examples of a 738 cc touring model, the G15/45, in 1962–63, but it proved even less reliable than the 650 when ridden hard and the planned 750 cc desert racer was abandoned. By then the company was in financial trouble, and G12 production ended in 1966.
Design and features
- Long-stroke 650: the 646 cc twin was created by lengthening the Model 11’s stroke rather than boring out its cylinders.
- Duplex frame: the 1959 De Luxe brought a full cradle tubular duplex frame and a new cylinder head.
- Siamese exhaust: the CSR’s two-into-one system, uprated cams and 8.5:1 compression set it apart from the 7.5:1 standard models.
- Teledraulic fork: the CS kept the Teledraulic front fork, praised for its behaviour off road.
Matchless G12 versions
- G12 De Luxe (1959–): the modernised road model with the duplex frame.
- G12 CS: scrambler-styled desert racer with more ground clearance and an upswept exhaust.
- G12 CSR / Monarch / Apache: the sporting roadster with siamese exhaust and twin carburettors from 1963.
- G15/45: a 738 cc touring model, 212 built in 1962–63.
- AJS Model 31: the same motorcycle sold under the AJS badge.
The G12 sat above the 500 cc Matchless G9 in the range and shared its chassis ideas with the G80. More Matchless motorcycles are in the Matchless collection.
Video: Matchless G12
Video on YouTube.
Sources
- Matchless G12, English Wikipedia: development, versions, production
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