Retrospective: BSA A7 Shooting Star 500cc: 1954-1962
That Daytona 200 was a thriller back in ’54, on a cold wind-swept beach. The 4.1-mile oval had one straightaway on the asphalt, then two 180-degree turns and the second straight on the sand.
Off the starting line, two Harley K-models, 750cc side-valve motors, led the way. These were the old days when 750 flatheads raced against 500 overheads. After five laps, a Triumph Tiger 500 took over. But by lap 20, a BSA Shooting Star ridden by Bobby Hill was leading the pack. In the 40th lap, Shooting Stars had first, second, fourth and fifth places, with a BSA Gold Star single in the middle. And that was how the race ended eight laps later, with BSA looking forward to a golden year of sales.
Truth be known, there was nothing really exceptional about the A7 Shooting Star.
It was just a strong, reliable machine that could withstand 200 miles of abuse. Only 44 riders completed the race, with 107 having started. Both riders and motorcycles had to have a lot of stamina. In the interest of transparency, it should be noted that Hill was using a Shooting Star engine in a rigid frame, the bike weighing some 50 pounds less than the swingarm machine; this was available through special order, mostly by racers, up through late 1953.
BSA’s A7, a 500cc twin, first appeared on the market back in 1946. After the success of Triumph’s vertical twin design in 1938, BSA immediately began planning its own version, but it had to appear sufficiently different from the Triumph design, since nobody wanted to be accused of being a copycat. World War II interrupted everything, but in 1946 BSA presented its new vertical twin, with a narrow bore of 62mm, a long stroke of 82mm, using a single gear-driven camshaft set behind the cylinders—Triumph had two cams, fore and aft of the cylinders. The fork was telescopic, but the frame was rigid. The factory claimed 26 horsepower at 6,000 rpm.
Power output was limited by the small combustion chambers and the low quality of post-war gasoline. A sporty version called the Star Twin was introduced in 1949, with twin carbs, a higher compression ratio and five more horsepower. And a plungerstyle sprung frame. Also arriving on the BSA scene at that time was designer/engineer Bert Hopwood, who was asked to come up with a larger version of the twin to compete with Triumph’s impending new 650 Thunderbird. And for cost-efficiency, could he please make as many pieces compatible between the 500 and 650?
The first thing Hopwood did on the A7 500 was to change the cylinder configuration, expanding the bore to 66mm and reducing the stroke to 72.6mm, thus creating a larger and more efficient combustion chamber… and the ability to rev a little faster. As a practical machine, buyers liked the A7 better than the new 650 A10, as it ran more smoothly…but Americans weren’t practical, and were usually happy to spend a few dollars more and get the 650.
In 1952, the West Coast BSA importer Hap Alzina decided to have a go for the Class C (essentially stock) 500cc speed record, and after a little legal massaging clocked a two-way average of 123.69 mph at Bonneville. People took notice. In ’53, a new alloy cylinder head was developed using just a single Amal Monobloc carburetor, which was bolted onto the Star Twin. Note the nice little “spill” tray under the carburetor—since the starting drill recommended pressing the tickler on the float bowl until gas came out, this was the way to avoid any excess drip onto the magneto, which sat behind the cylinders. The dynamo was in front.
A major change for the ’54 and later A7s was a new swingarm frame that had been developed, with the engine still sitting in the traditionally British cradle frame with double downtubes and the wheelbase extended just one inch, to 56 inches. There was the inevitable increase in weight—the swingarm arrangement adding over 30 pounds to the plunger models.
The standard, or “popularly priced,” A7 was now called the Flash, while the sporting version was no longer the Star Twin but renamed the Shooting Star, or SS for short. This had a slightly “hotter” camshaft than the basic Flash, and a slightly increased compression ratio; the SS was now rated at 32 horses at 6,250 rpm. The English road testers found the Flash and SS to be preferable to the bigger 650s, as the engine ran more smoothly. Americans, on the other hand, were convinced that there was no substitute for cubic inches.
The fact that few English motorcyclists in the mid-1950s could also afford an automobile resulted in major differences between the British and American approaches to motorcycling. Brits saw their motorcycles as practical transportation first, high-speed toys second.
Practical meant things like valanced fenders to keep the water off on rainy days. And that little cover, called a nacelle, over the headlight conveniently held the speedo, ammeter and headlight switch.
But Yanks were not practical motorcyclists, as most of them owned cars, as well. When they saw pictures of Hill’s machine, stripped for racing, they liked the idea of light fenders and detachable headlights. And it was very sexy to have a tachometer alongside the speedometer. This stripped notion was becoming the key to successful styling for the U.S. market.
Gradually, grudgingly, the boys in Birmingham acceded to the Americans’ wishes, sportifying the 650 Super Rocket and 500 single Gold Star, but neglecting the Shooting Star, going only so far as to lighten the fenders. That headlight nacelle was going to stay. Triumph elected to remove the headlamp shell from its own TR5 in ’58, increasing its sales-worthiness.
One mildly astounding example of BSA’s backward look was the company’s efforts to introduce the 600cc Commander into the U.S. market in 1957. This dowdy old lady, called a “utility” model, was intended to pull a sidecar and had a flathead engine in a rigid frame that had been around since before the war. What were they thinking?
But major changes were in the offing in the Brit-bike world. Four-stroke engines were going to unit construction, with gearbox bolted to the crankcase. Triumph was first with its 350 twin in 1957, and BSA followed with its 250 single in 1959. Then, in January of ’62, BSA announced the arrival of new unit 500 and 650 twins. But in the American market, sales of the 650s beat out the 500s some 10 to one.
(This Retrospective article was published in the July 2013 issue of Rider magazine.)