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

  • BSA Norton
    BSA and Norton responded to the twin format with their own take, but each adopted design approaches that were different from the other — and from Triumph.
    Photo By Robert Smith
  • BSA
    The A7 powertrain went into a conventional lug-and-braze mild steel tube frame, with a rigid rear and BSA’s own telescopic fork at the front, though the frame did make somewhat ingenious use of the seat tube.
    Photo By Robert Smith
  • Norton Side
    The Norton makes 29 horsepower.
    Photo By Robert Smith
  • BSA Twin
    The BSA’s twin makes 26 horsepower.
    Photo By Robert Smith
  • Norton Gauges
    The Norton Model 7 used a built-up crankshaft, with the inside webs bolted together through an integral flywheel.
    Photo By Robert Smith
  • BSA Top View
    The BSA A7 is functional and spare, almost stark — especially its rigid frame — though the gas tank is lavishly chrome-plated, a BSA hallmark.
    Photo By Robert Smith
  • Norton Model 7
    Presumably to avoid infringing BSA patents, Norton chief designer Bert Hopwood positioned the single camshaft at the front of the engine instead of the rear, driven by chain from a half-time gear.
    Photo By Robert Smith
  • BSA v Norton
    The BSA A7 and the Norton Model 7 may look quite alike, but the Norton feels more precise going down the road.
    Photo By Robert Smith
  • Riding
    BSA owner Dave Higgs (left) rides with Norton owner Jim Bush.
    Photo By Robert Smith

  • BSA Norton
  • BSA
  • Norton Side
  • BSA Twin
  • Norton Gauges
  • BSA Top View
  • Norton Model 7
  • BSA v Norton
  • Riding

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.






November December Vintage Motorcycle Events

Blue Moon Cycle Euro Bike Swap Meet and Vintage Ride


Make plans for the 28th Annual Blue Moon Cycle Euro Bike Swap Meet on Saturday, Oct. 27, followed by the Blue Moon Cycle Vintage Ride on Sunday, Oct. 28!

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