1957 MATCHLESS G11 BACKGROUND Matchless entered the vertical twin race in 1949 with the 500cc G9 and its sister-bike, the AJS Model 20. Both shared the same basic engine, which was unique among British vertical twins because it had a center main bearing. This made for a much stronger, smoother engine. In late 1955 they completed work on an enlarged version, now with 593cc (600) resulting from a near-square 72mm X 72.8mm bore and stroke. The resulting motorcycles were the Matchless G11 and the AJS Model 30. They were meant to be a stopgap between the 500cc G9 and the yet-to-be-introduced 650cc G12. Hence the Matchless G11 and AJS Model 30 were only produced from 1955 through 1959, overlapping production of the new 650 G12 which launched in 1958.