Comparing the BSA A7 and Norton Model 7

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

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

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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.

The BSA A7 engine was built around a one-piece iron crankshaft with a bolt-on flywheel and steel connecting rods, the crank running on a ball bearing on the primary side and a steel-backed bronze bushing on the timing-side, through which oil was fed to the connecting rod big ends. The timing-side bush was the engine’s weak point, and a point of much criticism over the years, especially as it was carried over to BSA’s later twins, which produced more than twice the A7’s horsepower. Worn bushings were often blamed for lubrication failure and engine blow ups.

A train of three gears drove the single camshaft, which in turn spun the magneto, while the front-mounted 6-volt generator was driven by chain. The cylinder block and head were cast in iron with siamesed intake ports for a single Amal carburetor and splayed exhaust ports.

The long stroke (62mm x 82mm) engine produced a modest 26 horsepower at 6,000rpm. A BSA 4-speed gearbox was bolted to the rear of the engine in “semi-unit” construction instead of separately to the frame. This was carried over into the first generation 650cc A10 Golden Flash of 1950.

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. Inside the tube, at the bottom, was a serrated rod attached to a steel bar that served as the centerstand. The stand was deployed by a ratcheting handle on the seat tube, which cranked the stand down to the ground, locking it in place with a pawl. Most owners quickly removed these stands as they had a habit of self-deploying while underway!

Another clever feature was a quickly detachable rear wheel — useful in those dark days of frequent punctures — and BSA’s patented “crinkle” hub that allowed the use of straight spokes. This design stayed with BSA for another 24 years. Dry weight for the A7 was 365 pounds, about 10 pounds lighter than Triumph’s Speed Twin.

Norton Model 7

Claimed power: 29hp @ 6,000rpm
Top Speed: 90mph
Engine: 497cc air-cooled OHV parallel twin, 66mm x 72.6mm bore and stroke, 6.7:1 compression ratio
Weight (dry): 413lb (118kg)
Fuel capacity/MPG: 4.2gal (16ltr)
Price then/now: $685 (est.)/$6,000-$10,000

Norton took a different approach designing their first parallel twin, the Model 7 Dominator of 1949. 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. He also arranged the cylinder head with widely splayed exhaust ports for more efficient cooling, and used a relatively shallow combustion chamber with a smaller included valve angle for better “swirl” and hence greater efficiency. The Norton Model 7 used a built-up crankshaft, with the inside webs bolted together through an integral flywheel. This assembly was supported by timing-side ball and primary drive-side roller main bearings, with flat top pistons connected to the crank via forged light alloy connecting rods. It’s worth noting that of all the British manufacturers, only Matchless/AJS saw the need for a center main bearing; yet when Honda started building parallel twins, they all featured three or even four mains!

The new engine pretty much slotted straight into the frame, transmission and cycle parts of the 1949 ES2 OHV single, meaning it used the “Garden Gate”-style frame with plunger rear suspension. Producing 29 horsepower at 6,000rpm, the twin gave much livelier performance than the 21 horsepower ES2, though at 413 pounds dry it was about 30 pounds heavier than the ES2 and some 38 pounds heavier than rival Triumph’s Speed Twin.

Side by side 

Though Norton is now considered one of the great motorcycle marques, it was a relatively small manufacturer in the early 1950s, with its main focus being racing — so much so that their bottom line was frequently written in red ink. As a result, Associated Motorcycles (the Matchless and AJS parent) absorbed Norton in 1952. BSA, meanwhile, had become one of Britain’s biggest industrial conglomerates, making everything from armaments to London taxis. Putting the companies’ first twins side by side reveals a lot about the relative approaches taken by their makers.

The BSA A7 is functional and spare, almost stark — especially its rigid frame — though the gas tank is lavishly chrome-plated, a BSA hallmark. The Norton Model 7, meanwhile, exudes quality. It’s understated and conservative, substantially engineered and a bit classier than the brasher Beezer. If not for the Korean War chrome shortage, it’s likely the Model 7 would have had a plated tank as well, yet the Norton’s silver paint and pinstriping make the BSA look gaudy and cheap by contrast. Jayne Mansfield meets the Queen Mother, perhaps?

Is this a fair comparison, you might ask, given that our sample BSA dates from 1949, while the Norton is a 1952 model? We think it is, as Norton was three years behind BSA in launching a twin, and both these bikes are their makers’ first twins. The Perkins A7 was replaced in 1950 by a new Bert Hopwood design based on the 650cc A10 Flash, while Norton’s 500cc Model 7 engine continued, with suitable upgrades, into the Sixties, both in a new swingarm single downtube frame as the Model 77, and fitted in the famous Featherbed frame as the Dominator 88.

BSA A7: Owner’s view 

“I’m the second owner of the bike,” says Dave Higgs, who lives in Vancouver, British Columbia, Canada. “The original owner bought it brand new and rode it until he died. I’ve just eclipsed him in length of ownership. I’ve owned it 32 years; he owned it 31.” Higgs bought the 1949 BSA A7 while he was still living in Bristol, U.K., from the previous owner’s son, who had started to dismantle it. Higgs rode it home! “Which was amazing given its dilapidated state,” he says. “It was dragged out of a shed, mostly complete — complete because everything was in the right place, but incomplete in the sense that not everything was original.”

Higgs spotted right away that the dual seat on a rigid frame wasn’t right, but sad though the Beezer was, his neighbor Harold persuaded him to keep it. The sight of the Beezer got Harold recounting tales of all the bikes he’d owned and sold. Each story was punctuated with a wistful gaze and “I wish I’d never sold that bike …”

“Ever since then, aged 17 I guess I was, I decided I’m never going to have to recount that story,” Higgs proclaims. “It’s very simple: I just won’t get rid of it. So I haven’t.” Higgs kept his word, even through a rocky relationship that led to the sale of his house, which left nowhere to store the BSA, then in a thousand pieces following his first attempt at restoration. “I had nowhere to live and nowhere to put the bike,” he says. “I knew this guy who was a restorer, though I think he did it more for love than money. So I asked him to put the bike back together.”

Back in 1980 there was no Internet, of course, so finding parts for the BSA took seven years of swap meets, letters and phone calls. “He managed to track down everything I needed. I don’t claim to have done the original restoration, but subsequent restorations I have done. In 32 years of ownership, it’s about a 10-year cycle.”

Higgs has rebuilt the engine more than once in an attempt to cure oil leaks. The A7 has a timed breather (engineer Perkins was very proud of it), which directs oil on to the final drive chain. A good idea, except that it throws surplus oil all over the rear of the bike, so Higgs modified it to direct the oil away. He also machined the primary case for a lip seal to replace the felt packing used by the factory. And while the engine was apart, Higgs epoxy powder-coated the inside of the crankcases to prevent oil seeping through the porous castings.

“I’ve worked extremely hard to get the thing oil-tight,” Higgs says. “One more change I would make is to go from the mechanical regulator to an electronic one, because they’re useless.”

So what’s it like to ride? “It’s not a revvy engine; it’s a long stroke and it’s very heavy. I think it was designed for plowing!” Higgs says. “The brakes are awful. The back brake is good because of the long pedal arm, but the front is terrible. Fortunately, you don’t get great speed out of the thing. It’s the bike I took my [motorcycle endorsement] test on when I came to Canada. It’s very good at low speeds because of the gentle fork rake.”

Higgs also rode Jim Bush’s Norton Model 7. “I thought it was a much more sophisticated ride than mine, the power delivery especially. Very smooth on the clutch, very positive acceleration.

“On the BSA, you roll off the throttle, pull in the clutch, you wait, push down on the lever. It’s a process, while the Norton seems to have just this feel of sophistication where you would just change gear, up or down. I can go up to fourth fairly quickly, but downshifting on the BSA I have to be careful, otherwise it grinds and graunches and you find how many neutrals you’ve got!

“My bike felt lighter, so I think his has a little more weight. It didn’t feel as jittery as mine. The ride just felt more sophisticated, for sure.”

Norton Model 7: Owner’s view 

Hanging on the wall over Jim Bush’s home office desk in Surrey, British Columbia, Canada, is a large sign that reads, “Don’t buy any more motorcycles!”

Even so, surfing eBay one night, Bush stumbled on a Norton Model 7 with just eight minutes left in the auction. Ignoring the sign, he placed a bid to test the waters and found he was still high bidder when the auction closed.

The Norton belonged to a serviceman in Mountain Home, Idaho, who had bought it while stationed in the U.K. Restored in 1981, the bike had not been started until tested in 2002 by Classic Bike Guide magazine, and was then sold by U.K. dealers Clarke’s Classics. Its condition appears unchanged — complete, faithfully restored and in first-class shape. Best of all, it wasn’t over-restored: the chrome glows, the alloy is lustrous, and the paint softly radiant. The 7 was showing just 2,000 miles when Bush bought it, but its long repose didn’t cause any issues: It starts easily (thanks to a powerful magneto), runs strongly and has been perfectly reliable. Even the charging system works — thanks to a modern solid-state generator regulator.

“The motor has a softness to it,” Bush says. “It’s easy starting, easy riding; and it’s all about coaxing — coaxing to speed and coaxing to a stop. Riding at 55-60mph on the highway seems very comfortable. It’s not over-revving, it’s quite smooth.

“I don’t like to take it over 60, though I’ve been up to 75 on a slight downhill. But with a wiggly, plungered frame and spindly forks with no brakes, you don’t really feel that comfortable. It’ll go all day at 55mph. It just hums. And even when you come to a hill, it’ll still accelerate. It has a low center of gravity, which for me always seems to enhance handling. It feels very stable.” Especially compared to a sprung hub Triumph he used to own, Bush says.

“The plunger seems very relaxed,” Bush continues. “The sprung seat may also make a difference. It’s got the big 21-inch diameter front wheel, so it tracks really well. And being a twin, it’s really smooth. Try doing 55mph on an ES2! I always really wanted a big single, but now I’m happy I got a twin. And I ride it everywhere.

“It has some finesse and a general feeling of superiority, compared with the Triumphs I’ve ridden,” Bush says. “That’s definitely the feeling of that bike: quality. I think the Model 7 was built to a superior level. It does feel like it.”

In the final analysis they’re both desirable, but perhaps for different reasons. They both share the distinction of being their maker’s first twin, and they’re both lovely to look at. The BSA came first, giving it an edge for being first to follow Triumph’s lead. But the Norton is clearly the better rider, making it the better rival to Triumph’s iconic Speed Twin. MC