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In the early fifties the most popular British four-strokes were still pushrod singles. 500cc machines typical of this era were the Matchless G80 and the AJS Model 18, both manufactured by Associated Motor Cycles (AMC) in London. The two aforementioned models were made in the same factory, the only difference in the two being the position of their chain-driven magnetos.

The magneto in the AJS was in front of the cylinder, where the Matchless was behind. The position of the magneto on the AJS allowed access to the separate dynamo. The Model 18S was a little heavy but it offered much better performance and fuel economy than the fast cars of the same era.

A design from the 1930s, being manufactured 30 years on, the AJS was updated when a spring frame rear suspension was included (hence the 'S'). The suspension was a vast improvement on the bouncy rear end but the wheel travel was only 75mm.

The Engine

A modest performance from the low compression engine in 1950 was brought about by conditions in Britain at the ime. Petrol rationing was abolished in 1950 but branded fuels did not return to the High Street until 1953. If you couldn't get your hands on high-octane aircraft fuel you were limited to standard low-octane 'Pool' petrol. A compression ratio of 6:1 would have caused the engine to overheat and damage the piston and valves.

The good thing about low compression was that it was easy to kickstart and had more flexibility at low revs. The AJS wouldn't reach 80mph but it would go along at less than 20mph in top gear. This meant that a small amount of petrol went a long way.

Shocking Development
AMC designed its own telescopic front fork for the 1941 Matchless G3/L, but they chose to copy Velocette's twin-shock swingarm rear suspension for it's top of the range AJS and Matchless singles and twins. Shorter vertical units were introduced in 1949. The 'Candlestick' shocks had only 50cc of SAE 20 oil in each damper. They were prone to bottom-out and leak and had drain and filler plugs which encouraged the owners to overfill the dampers, meaning further leakage. 'Jampot' shock replaced these on the 1951 version.

Production : 1949-1963
Engine type : Single cylinder, pushrod 2 valve, 4 stroke
Capacity : 498cc
Bore and Stroke : 82.5 x 93mm
Compression Ratio : 5.9:1
Fuel System : 27mm Amal Carburettor
Power : 23PS @ 5,400rpm
Dry weight : 177kg
Top Speed : 78mph