BSA A10 series
The BSA A10 series was a range of air-cooled parallel twin motorcycles designed by Bert Hopwood and produced by Birmingham Small Arms Company at Small Heath, Birmingham from 1950 to 1963. The series was succeeded by the A65 unit construction models. Background BSA, then the largest UK motorcycle manufacturer, was falling behind in the parallel-twin race after the introduction of the 650cc Triumph Thunderbird. Although BSA had a 500cc parallel-twin, the BSA A7, they needed to develop a 650 to remain competitive. Bert Hopwood served an apprenticeship under designer Val Page at Ariel. In 1936, Hopwood moved to Triumph, where he worked under Edward Turner to develop the 1937 Triumph Speed Twin. The innovative Speed Twin became the exemplar of the parallel twin engine layout for British motorcycles in the 1950s and 1960s. In April 1947 Hopwood joined Norton to design the Norton Dominator engine. In May 1948, the factory enticed Hopwood after only a year at Norton, and he was commissioned to create a competitive BSA 650cc parallel-twin. Development Engine Launched in October 1949, Hopwood's A10 Golden Flash drew heavily from the A7 design by Page and Bert Perkins. The A10 was increased to by using a 70mm bore