1961 Matchless G12 CSR Motorcycle

Description

One of the last motorcycles produced by Associated Motorcycles using the Matchless name, the G12 was sold alongside the almost identical AJS Model 31.  Using as many parts from the existing AJS Model 11 as possible, AMC designer Phil Walker lengthened the stroke from 72.8 to 79.3mm, giving a total capacity of 646cc, using a new crankshaft and primary chain case, along with a Lucas alternator.  Aimed specifically at the potentially lucrative American market, volume production began in September 1958 and the final G12 rolled out of the Plumstead factory in London eight years later.  Major updates throughout the G12’s production life included the De Luxe model of 1959 with a new full cradle tubular duplex frame, a new crankshaft designed to cure vibration issues and a redesigned cylinder head.  An off-road model with better ground clearance, designated the CS, was added to the range, while the CSR (which stood for Competition Sprung Roadster although many pundits dubbed it the “Coffee Shop Racer”) from May 1962 offered even better performance thanks to a special two-into-one exhaust, raised compression ratio and hotter camshafts.  For 1963 twin carburettors were added and the G12 CSR gained the Monarch name, while the AJS version was badged the Hurricane.  Issues with leaks and vibrations saw Chief Engineer Jack Williams diverted from developing the AJS 7R to cure the problems and modify the CSR for racing, resulting in Ron Langston and Don Chapman winning the prestigious Thuxton 500 endurance race on the AJS Model 31 counterpart.