Description
BSA 1950 A7 495cc vertical twin frame # ZA7 R4411 engine # ZA7 R7779
In 1937 Triumph launches its Speed Twin which becomes a great success. BSA can’t stay behind so the company starts to develop a vertical twin in the years before the war. This model is to make its appearance in 1940 but by this time BSA gets very much involved in the war effort and the launch of new models is postponed. In September 1946 the new twin becomes available as the A7; it is the first of a long line of powerful and reliable parallel twins that carry the Piled Arms trademark.
The first A7 models have long stroke engine dimensions of 62x82mm and have a semi-unit construction: the gearbox is bolted to the back of the crankcase. Primary drive is by duplex chain, chain driven dynamo is in front of the cylinder block, gear driven magneto is positioned behind. Both pistons rise and fall together on the 360 degree crankshaft. Compression ratio is 6.5:1 and the engine delivers 26 hp @ 6000 rpm. In 1949 a twin carb version, the Star Twin, becomes available together with a plunger frame that is optional on the A7 and standard on the Star Twin.
In the course of 1951 a change in bore and stroke to 66×72.6mm is effected to reach a cubic capacity of 497cc. The introduction of the new duplex frame means that the original A7’s bolted-up gearbox has to go. Production of the venerable A7 ends in 1961.
This well-restored A7 is finished in Devon Red and is a fine runner. She comes with current Dutch registration and Smiths 120 mph speedo.