AJS 18 - Engine

Engine

The engine was released just postwar with a compression ratio of 5.9:1, necessary because of the low quality fuel available in Britain immediately after the War. British singles were designed to make the best of the fuel available. Post war petrol rationing continued until 1950 and it was several years before performance fuels were generally available in the UK. The Model 18’s low compression did mean it was easy to start and The model 18:s had better performance and fuel economy than the fast cars of the time.

By 1951 the model 18 had an alloy cylinder head and the competition models had also an alloy cylinder (with steel liner in it), where the barrel fins went all the way to the base. The magneto was moved in front of the cylinder on the Matchless G80 for 1952. The earlier model did not have a magdyno - the separate magneto was directly above the dynamo behind the cylinder. The leaky pressed-steel primary chain-case that first appeared in early times had a small clutch inspection/adjustment plate added in 1952 and in 1954 the whole clutch dome was replaceable in it. The compression ratio was increased to 8.7:1 in 1956 and in 1958 an alloy cover primary chain-case became available.

The unreliable 'jampot' shock absorbers were replaced with Girling shocks in 1956 and in 1957 AMC switched from Burman gearboxes to their own make. In 1960 the model 18 gained a duplex frame.