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. BSA, then the largest UK motorcycle manufacturer, was falling behind in the parallel-twin race. Although BSA had a parallel-twin, the BSA A7, they needed to develop the bike to remain competitive. In May 1948, the factory enticed Hopwood after only a year at Norton, and he was commissioned to create a competitive BSA parallel-twin. 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, with a revised alloy rocker box and cast-iron cylinder head, plus an integral manifold for the single Amal carburettor. A semi-unit gearbox meant the primary chain was adjustable via a slipper tensioner within the primary chain case. The frame was available in rear rigid format, but the more common option was plunger suspension, adopted for the export market. The A10 featured a hinged rear mudguard to ease rear wheel removal. The A10 was so closely based on the A7 that it used many of its well-proven components, and this large carry-over of parts from the A7 promised greater reliability, with minimal risk of new technical problems.
Production
The BSA Golden Flash was launched in a new gold colour, and 80% of production was destined for the United States. This resulted in long delivery times for British customers, who were offered the model only in black. Although never designed as a sport motorcycle, the Golden Flash was nonetheless fast for its time and competitive with the Triumph Tiger 100, achieving over in tests in 1950, and covering a standing quarter mile in under 16 seconds. Its gold colour proved a marketing success, outselling Triumph's Speed Twin and 6T Thunderbird. BSA were concerned that wear in the plunger suspension was leading to uncertain handling. In 1954 the factory adopted a swinging arm, and the hinged mudguard was deleted. In a seemingly backwards step, the semi-unit gearbox was abandoned for a separate "pre-unit" item. The new design had a different primary chain adjustment, a modified clutch, and new gearbox internals. A tuned version. the Super Flash was available in the US in 1963 - 1964. Following requests for a more powerful version from the US, the engine was turned with parts from the competition department. This was an interim measure whilst sports bike version of the A10, the Road Rocket was being developed. In 1957 an improved clutch was introduced, using 4 springs instead of six and improved friction material. For better reliability, the Golden Flash was upgraded in 1958 to the "thick flange" cylinders and larger big ends originally fitted to the Road Rocket. For 1960 the model was fitted with the 356 sports camshaft and a larger 389 Monobloc carburettor. It was renamed the "Royal Tourist" in the US. An alternator was offered as an alternative to the dynamo from 1961 to 1963, the last three years of production. In the late 1950s, motorcycle electrical component manufacturer Lucas decided to switch production from magneto/dynamo systems to alternators/coil systems. This forced British motorcycle manufacturers to completely redesign their engines. With the launch of the new unit constructionBSA A50 and BSA A65, the A7 and A10 were discontinued in 1963.
