BSA A7
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| Manufacturer | BSA |
|---|---|
| Production | 1946 |
| Engine | 495 and 497 cc (30.2 and 30.3 cu in) straight twin |
| Top speed | 85 mph (137 km/h) (495) 90 mph (140 km/h) (497) |
| Power | 26 bhp (19 kW) (495) 30 bhp (22 kW) @ 5800 rpm (497) |
| Transmission | Duplex primary chain to bolted up unit gearbox |
| Wheelbase | 1,391 mm (54.75 in) |
| Weight | 166 kilograms (366 lb) (dry) |
| Fuel capacity | 3.5 imp gal (16 L) |
The BSA A7 was a motorcycle made by Birmingham Small Arms Company (BSA) at their factory in Armoury Road, Small Heath, Birmingham in 1946. There were two versions of the A7, the original 495 cc (30.2 cu in) version, and an improved 497 cc (30.3 cu in) version launched in 1950. Although its name was changed to the Star Twin and later the Shooting Star the BSA A7 continued in production with minor modifications until 1961.
Designed by Val Page, Herbert Parker and David Munro, the BSA A7 was the first of the BSA twin-cylinder motorcycles and was ready for launch in 1939, but the outbreak of World War II delayed the launch until September 1946 when hostilities ended. The very first A7 off the production line was flown to Paris for the first motorcycle show after the end of the war. There was huge demand for affordable transport after the war and the simplicity of the A7 twin was helped along by the slogan 'It's time YOU had a BSA!'.
The 495 cc (30.2 cu in) twin cylinder engine produced 26 bhp (19 kW) and was capable of 85 mph (137 km/h). A single camshaft behind the cylinders operated the valves via long pushrods passing through a tunnel in the cast iron block. This system needed a considerable number of studs and nuts to fasten down the cylinder head and rockerboxes, many of them deeply recessed and requiring well-made box spanners or the then uncommon sockets. As with other British motorcycles of the period, this kind of set-up regularly led to oil leaks.
Most motorcycles of this period tensioned the primary chain by drawing or rotating the gearbox backwards on a hinge with threaded rods, this was known as pre-unit construction. The first A7 had a fixed gearbox, bolted to the back of the crankcase, and an internal tensioner for the duplex primary chain. This gave it the appearance of unit construction and pioneered the system later used in unit-construction engines such as the BSA C15, BSA B40, Triumph 3TA and so on. However, in 1954 a re-design reverted to the older system. The electrics (as was universal for larger British motorcycles of the period) consisted of two independent systems, the very reliable and self-contained Lucas magneto, with a dynamo generator to charge the battery and provide lights. Carburation was a single Amal remote float Type 6 until 1955 when it was upgraded to a 376 Monobloc.
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