Sure-Footed Shooting Star

Smooth and steady all-rounder

- Marion Thirsk

DEVELOPED DURING THE late 1930s, BSA’s first parallel twin was launched in 1946. Triumph’s 500 Speed Twin may have been faster but the A7 quickly gained a reputation for being quieter, dependable and significantly more oil tight. Proving popular, the A7 was given one significant revamp and then continuously tweaked and improved throughout a 16-year production run.

The early A7 twins featured a cast iron cylinder head and block with a bore and stroke of 62mm by 82mm to give 495cc, reaching 27bhp at 5800rpm. At a time when most manufacturers were using twin camshafts, BSA cut costs with a gear-driven single camshaft operating overhead valves via four pushrods. Two separate aluminium alloy rocker boxes were fitted with Edward Turner-influenced screw caps. A neat ‘semi-unit’ gearbox was bolted to the rear of the crankcase with primary chain tensioning achieved by means of a curved slipper tensioner. This was adjusted by a screw-in bolt with a lock nut. Both wheels were quickly detachable. The early, longer stroke single carb A7 engine lasted four years, with a sports variant, the higher compression twin carb A7 Special (soon renamed the Star Twin with plunger frame) enjoying a power increase to 31bhp at 6000rpm.