1962 BSA A50 Royal Star

The last of the "utilitarian" 500s
By Clement Salvadori
July/August 2011
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The 1962 BSA A50 Royal Star.
Photo by Clement Salvadori
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1962 BSA A50 Royal Star
Claimed power:
28.5hp @ 6,000rpm
Top speed: 90mph (est.)
Engine: 499cc OHV air-cooled parallel twin
Weight (dry): 385lb (175kg)
Price then: $775 (est.)
Price now: $4,000-$6,000

In the late 1950s BSA was in a bit of a pickle. The Brits, still convinced their motorcycles were the world leaders, believed gentle improvements would keep them in the lead until the cows came home. Pushrod vertical twins, around for a quarter of a century already, would be the king of the hill for the foreseeable future.

Yet motorcycles were being hyped as ever bigger and faster, especially in the U.S. And while BSA had plenty of competition success to crow about, with wins at Daytona and Catalina Island, to name just a few, it was losing ground to higher performance, more modern twins from Triumph and Norton. Power was king, yet many of BSA’s conservative marketing types thought surely there were still sensible lads who would appreciate the reliable, easy to start, half-liter plodder. Good for commuting, maybe a trip to the continent, perhaps some low-speed sport on the week’s end. What to do? In the end, they tried to satisfy both, and this led to the development of the BSA A50 Royal Star.

New beginnings
The big news from BSA came in 1962, with the arrival of new unit-construction engines, available in the 500cc BSA A50 or the bored-out 650cc BSA A65. In England these were known as Star models, whereas in the U.S. they were called Royal Star. Curious that, since we Americans had fought a bloody revolutionary war to get rid of the monarchy, and now we appeared captivated by anything that smacked of royalty.

This had all begun a few years before, when the BSA suits finally realized that something had to be done to upgrade BSA’s famous parallel twin engines. These had been around since 1947, when the 500cc A7 Star Twin was introduced, followed by the 650cc A10 in 1950. The A7 stayed rather benign in the Fifties, though one version of the A10 was hotted up to become the best-selling Super Rocket in the U.S., competition for the Triumph Bonneville.

BSA had an understandable love/hate relationship with Triumph. Both were owned by the same company, but their badges kept them very much apart. In the U.S., Triumph consistently outsold BSA, which the Small Heath gang did not appreciate.

Early in 1960, the engineers at BSA’s R&D center got the word to redo the twins into a unit construction, as Triumph had already done with its own 350/500 twins. There was nothing especially radical in this, although it would require all new tooling, as a new engine and new frame would be required. One of BSA’s problems, and it was endemic to the entire British motorcycle industry, was getting its investors to actually invest in new designs; this was proving exceedingly difficult, and companies had to scrimp where they could.

Fraternal twins
To this end, except for the cylinders and heads, the A50 and A65 were almost identical. The under-square 500 (499cc) had a bore of 65.5mm and a stroke of 74mm, while the slightly over-square 650 (654cc) had a bore of 75mm, with similar 74mm stroke. Conventional parallel twin technology dictated a 360-degree one-piece crankshaft, pistons rising together and firing alternately, the crankshaft secured by bearings at each end, with no support in the middle.

This was standard practice, and engineers had to factor in the inevitable flexing of the crankshaft. The left end of the shaft, the primary drive side, sat in a ball bearing, a cheaper replacement for the roller bearing on the old A7/10. The less-stressed right end, the timing side, used a plain bearing, as had been used on the A7/10; on the new models this was increased in size, the better to cope with what the engineers hoped would be more power.

These bearings turned out to be the bête noire of these bikes. The ball-bearing, if irresponsibly thrashed, could self-destruct, causing unpleasant noises and damage. The plain bearing, from which side the dry-sump lubricating system worked, would, if it became too worn, fail to pass along an adequate supply of pressurized oil to the big ends, also not a good thing. These problems were not consistent, however, and mostly afflicted the 650. They were certainly not as dramatic on the modestly powered A50, which originally came in with a 7.5:1 compression ratio, developing 28.5 horsepower at 6,000rpm, according to the factory, as against the A65’s claimed 38 horsepower at a slightly lower 5,800rpm. Upgrades for 1965 included a roller bearing on the drive side, as it had been on the pre-unit engines, with an improved bronze bushing on the other end. This pretty much fixed the problems.

BSA used a single camshaft placed behind the iron cylinders, run by gears off the timing end of the crank. Four lightweight pushrods went up into the aluminum-alloy head, where the pillars holding the rocker spindles were part of the casting, providing excellent rigidity and reducing the need to check the valve clearance. A very nice aspect of the engine was that the single valve cover, when removed, provided excellent access to all four tappet adjustments. A Triumph had four individual caps, and the valve gap was always difficult to measure.

Another decided benefit of the new unit construction was a reduction in oil leaks. Oil passages were internalized, making for a much cleaner-running engine. Yet the Brits still persisted in splitting the crankcases vertically, instead of horizontally like the Japanese, an approach that was far more prone to leaving spots on a clean concrete garage floor.

Powering out
Electrics evolved from the previous magneto ignition with generator for lights to a 60-watt alternator on the drive end of the crankshaft and two coils with two set of points. All the electrics were produced by Joseph Lucas, of course, including the 13-amp, 6-volt battery. The points, hidden behind a small plate in the right cover, were actually very accessible. The system worked quite well, and there was even a dead-battery position for the key, enabling a start with a spark straight from the alternator.

A great advantage of the unit construction design was being able to run a triplex primary chain in an oil bath from the crankshaft to the transmission mainshaft, reducing the need for chain adjustment. Because of the possibility of misalignment, earlier pre-unit engines used a single chain, which was prone to stretching. Adjustment was a tedious task, done by loosening the gearbox and moving it backwards, requiring the final chain to be adjusted, as well. On the A50, all it required was raising a small slipper plate tensioned against the bottom of the triplex; job done. Further, the five-plate clutch had rubber buffers to absorb untoward shocks, useful in prolonging the life of a chain.

The transmission went down for first, up for second, third, fourth — the opposite of previous BSA twins. The Brits felt such newness could easily be overcome by a competent rider. There were occasional complaints about the new gearbox being a bit notchy, but these appeared to go away. Final drive was by single-row chain, with lubrication coming from the primary case. A full-enclosure for the chain was an option in England, but apparently came as standard in the U.S. with the A50.

Holding it together
All this required a new frame, and welded, tubular double cradles were the rage. The A50/65 used a design similar to the previous A7/10, with a single backbone and a massive steering head. Wheelbase was 54 inches, quite compact and two inches shorter than the predecessor A7/10. The engine was solidly bolted in, and while vibration could be a concern with some of the high-strung 650 versions, on the A50 this concern was negligible.

A pair of hydraulically damped Girling shocks with three preload adjustments took care of bumps out back. Up front, the BSA forks had compression damping, but could bounce off the top on the rebound if the going was exceptionally rough — like over railroad tracks at speed. Steering lock was a full 45 degrees on each side, making for a useful turning radius of 14 feet.

Wheels were 18-inchers, a 3.25-inch tire on the front, 3.5-inch on the rear. The A50 had 7-inch single-leading-shoe brakes with full-width hubs at both ends. Some comment was made about the front; the bigger A65 had an 8-incher, and reviewers could not understand why BSA opted for the smaller unit on the 500, as they both weighed about the same. There was only five pounds difference when put on the scale, the A50 weighing in at 385 pounds dry (about 35 pounds lighter than its A7 predecessor), and the A65 at 390 pounds, and they both could cruise at a pretty high rate of speed. The uncharitable said it had to do with cost and was a false economy.

Not cool enough?
By American standards, the tinware on the BSA A50 was downright dowdy, even if the bike was being touted as a touring motorcycle. A fully valanced fender might be efficient in the rain, but it sure didn’t look cool at the A&W drive-in on Saturday night. And then there was that headlight nacelle, very Fifties. We Yanks liked stand-alone headlights and stand-alone instruments, preferably chromed.

The three-gallon gas tank with chromed panels was fine, and the long flat saddle followed the standard of the day, but those side panels were a bit much. As in much too large. The left one covered the battery, the right the rubber-mounted oil tank and tool kit. Unfortunately, they extended forward beyond normal constraints, covering the single one-inch Amal Monobloc carb and air cleaner, to the degree that an extension had to be put on to enable the rider to “tickle” the carburetor when starting. The Brits seemed to like the tidiness, the colonials did not.

In 1964 an offroad version of the A50 — sans lights — appeared. The BSA Cyclone Competition had twin carbs, compression ratio raised to 9:1, and a claimed output of 38 horses. The following year the BSA Cyclone Road, with lights, optional rearset footpegs, as well as abbreviated fenders and side panels, was on the market, but sales were dismal. Why buy a hot-rod 500 when a 650 Lightning was only a few dollars more? Both Cyclones disappeared at the end of 1965, to be replaced by the twin-carbed A50 Wasp, available in offroad or on road trim. That combative insect was deleted in late 1968, again due to lack of buyers.

For 1966 the basic BSA A50, promoted as a “sports touring” motorcycle, got a cleaner look, with sportier fenders, separate headlight (chromed) and speedometer, and diminished side panels. And 12-volt electrics. And that much-desired eight 8-inch front brake on a 19-inch wheel. In 1967 the forks got two-way damping, and the next year the Monobloc carb was replaced by a 26mm Concentric.

But the constant improvements made little difference, as the only people who would appreciate them were in the realm of British motorcycles. The real challenge was coming from thousands of miles away, with the Japanese producing seriously impressive machinery, like rip-snorting two-stroke triples and overhead cam inline fours. British bike-makers, trying to make do with engine technology from the 1930s, were teetering on the edge of bankruptcy and hard decisions were being made. One was to reduce the number of BSA models, and 1970 was the last year for the A50. Royalty got the executioner’s axe a few years later, and for BSA it was all over. MC 

Resources
Parts: 
Walridge 
Brit Cycle 
Baxter Cycle 

Info:
Ohio Valley BSA Owners Club 


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