Comparing the BSA A7 and Norton Model 7

Head-to-head on a 1949 BSA A7 Twin and a 1952 Norton Model 7.

| July/August 2013

What if Harley-Davidson announced they were going to build an inline 4-cylinder motorcycle? Or Ducati said they would build a triple? It just wouldn't be right, would it?

Now imagine the furor surrounding Norton’s 1949 announcement that they would launch a twin-cylinder bike. From the time they started building their own engines in 1912, Norton had produced only singles, including sidevalve and overhead valve units and the famous overhead cam Manx. For Norton to forsake its heritage was something close to sacrilege — “Pa” Norton would be turning in his grave! But by 1949 it was clear that twins were the future and singles the past.

In 1938, Edward Turner’s Triumph Speed Twin redefined the British motorcycle, and by the end of the 1940s every manufacturer had to have a parallel twin in their lineup. BSA and Norton responded with their own take on the format, but each adopted design approaches that were different from the other — and from Triumph. How did they compare? And which one was better?

1949 BSA A7 Twin

Claimed power: 26hp @ 6,000rpm
Top speed: 85mph
Engine: 495cc air-cooled OHV parallel twin, 62mm x 82mm bore and stroke, 6.6:1 compression ratio
Weight (dry): 365lb (166kg)
Fuel capacity/MPG: 4.5gal (17ltr)/45-55mpg
Price then/now: $675 (est.)/$6,000-$10,000

BSA’s first parallel twin, the 500cc A7, was built from 1946-1950 and bears witness to several of Britain’s best motorcycle designers. Valentine Page is credited with the basic layout, and he had almost completed the design in 1939 before hostilities interrupted civilian bike development. Edward Turner of Triumph fame also worked on the BSA A7 project in the early 1940s before BSA’s Herbert Perkins completed the detail work.

The first production A7 engine also featured characteristics of Page’s 1935 Model 6/1, a 650cc parallel twin he designed for Triumph — the single camshaft mounted behind the cylinders, for example. (Turner’s Speed Twin used two camshafts.) But several of Turner’s styling hallmarks — like the separate rocker boxes with screw-on inspection caps — also endured.

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