1955 BSA A10 Golden Flash Plunger
With an experienced team and a lot of data.
The Triumph 500 cc Speed Twin of 1937 set the standard for vertical twins among British bike manufacturers, and designer Bert Hopwood created similar twins for different companies. Hopwood started out at Ariel under Val Page in 1936, and moved to Triumph to work under Edward Turner in 1937. He went to Norton in 1947, where he produced the Dominator 500 cc twin. Val Page had developed the 500 cc BSA A7 twin in 1946, but it did not work well and Hopwood was hired to fix it in 1948.
For 1949, Hopwood reshaped the A7 into the much better 650 cc A10, known as the Golden Flash for its most popular color. The BSA A10 Golden Flash was tested at 100 mph in 1950 and returned 16 seconds for a quarter mile. The cylinder head was still cast iron but the rocker box was alloy and an integral manifold carried the single Amal carburetor. A rigid rear end was available, but export models had plunger rear suspension. The gearbox was bolted to the back of the engine, and the primary chain could be adjusted by a slipper tensioner.
Hopwood applied the same internal improvements and use of light alloy to the A7, which resulted in the 500 cc Star Twin. Its sporting sibling was 1952’s A7SS Shooting Star. The Star Twin won the Maudes Trophy for reliability in 1952, when three bikes were ridden 1,000 miles to Austria to compete in the International Six Day Trials, then ridden home, for a total of almost 5,000 miles.
The plunger suspension compromised handling as it wore, so it was replaced with a conventional swing arm in 1954, and a more old-fashioned separate gearbox was adopted. That year, the twin-carburetor Road Rocket was introduced with an alloy cylinder head. The 105 mph Super Rocket followed in 1957 with 43 bhp from a high-lift camshaft and an Amal TT carburetor.
The final variation of the Rocket was the Rocket Gold Star of 1962-63. The RGS fitted the Super Rocket motor into the old Gold Star single frame for a very competitive ride. Lucas changed from mag/dynos to alternators and coil ignition in the late 1950s, forcing British manufacturers to adopt unit construction (which combined gearbox and crankcase castings) in 1962. The old A10 was replaced by the new unit-construction A50 and A65, but the A10 RGS soldiered on for another year with its separate gearbox.
The RGS package was sufficiently attractive (and now valuable) that many Rocket Gold Stars were created by enthusiasts who merely popped Super Rocket motors into ordinary Gold Star frames. As a result, there are many more RGS models on the road now than were ever built by the factory. Any potential purchase should be examined by an expert before hard-earned money changes hands.