The legendary AJS pushrod-engined racers (below) had logged plenty of wins from their introduction in 1920, announcing the end of the sidevalve era at the 1921 Isle of Man Junior TT by taking 1,2,3, then winning the Senior TT with the same 350cc, ridden by Howard R. Davies. The 'Big Port' appeared in 1921, and gained a racing reputation for winning over the next 5 years. Given the rapid technological development of the day, with many factories introducing OHV engines with their racers and roadsters, the Big Port had a fine run of success, but competition was keen from Norton, Sunbeam, and Douglas with their own OHV racers.
|The classic AJS 'Big Port' racer, ca.1925|
AJS chief engineer Phil Walker was given the task of designing a new engine in late 1926, and chose the simplicity of a chain drive to the camshaft, which had been problematic in past attempts due to chain whip over a long run at engine speed, but the new, patented Weller chain tensioner kept things under control well enough for Aston Martin racers, as well as aero engines. Shaft-and-bevel drive engines, as used by Chater-Lea and Velocette (and copied by Norton for the CS1 and Inter/Manx), were laborious to set up correctly, while the chain was simplicity itself, boding well for ease of manufacture and a lower sale price.
Junior TT and wins in the Swiss, Belgian, and European GPs, with Jimmy Simpson their pace-setter. Curiously, AJS chose to run their pushrod racers in the 1928 TT, making second place in the Senior TT, but for 1929 and beyond, they relied on the 'cammy' engines for racing, which led through the R7 racers of the 1930s, to the AJS 7R and Matchless G50 of the postwar era.