1960 BSA A10 Golden Flash

Though Bert Hopwood is generally credited with the design of BSA’s A10 engine, just about every important British motorcycle engineer had a hand in it. Hopwood’s final engine layout for the 1950 Golden Flash was really the culmination of 15 years of experiment, development and experience. Not surprisingly, Hopwood’s final effort is sometimes considered the most satisfactory design of British pre-unit parallel twins, though often overshadowed by Triumph and Norton offerings in the class.

The British parallel twin’s general layout can be traced to Valentine Page’s Triumph 6/1 of 1934 (Motorcycle Classics, May/June 2013), which itself borrowed ideas from Edward Turner’s 1931 Square Four, from when both designers worked at Ariel. When Page moved to Triumph from Ariel, it wasn’t long before the 6/1 appeared using an overhung crank and gear primary drive — both features of Edward Turner’s original Square Four design. The 6/1 used a single camshaft mounted behind the crank, a feature that was to appear later on the A10 engine.

Meanwhile, Edward Turner had also moved to Triumph (Page quickly departed for BSA) and immediately scrapped the 6/1, starting work on his own parallel twin that would become the Speed Twin of 1938. This was such a commercial success that the other British makers had to play catchup with their own parallel twins. Page had started work on a parallel twin at BSA before World War II interrupted. It included two features from the 6/1: the single camshaft behind the crank; and the gearbox bolted to the back of the engine in what was to become known as “semi-unit” construction. Edward Turner himself worked at BSA during the war years after the Triumph factory was destroyed in the Coventry “blitz” in 1940 and left his own mark on what was BSA’s first parallel twin, the 500cc A7 Twin of 1946. Turner’s influence was indicated in the design of the rocker boxes and hex-cap covers, the elegant timing cover, and the choice of a plain bearing crankshaft.

With Turner back at Triumph, final design work on the A7 fell to BSA’s Chief Designer Herbert Perkins. Perkins’ engine retained features of Page’s design, like the single camshaft and semi-unit construction. He also revised the rocker oil feed with positive lubrication rather than oil mist. So BSA’s first parallel twin featured a one-piece crankshaft with bolt-on flywheel, ball bearing main on the drive side and a plain bush on the timing side. Though this bush was considered the Achilles Heel of the A7/A10 design, it rarely failed if engine oil was changed frequently. It survived the transition to unit construction in 1963 and was still used in the last BSA 650s of 1972.

Drive to the camshaft was by gears, which also spun the magneto, with chain drive to the front-mounted 6-volt DC generator. A chain-driven 6-plate clutch transferred power to the 4-speed BSA gearbox. The A7’s duplex steel tube frame was rigid at the rear and fitted with BSA’s own hydraulic front fork. Seven-inch, single-leading-shoe drum brakes were fitted to the 19-inch wheels. One ingenious feature of the frame was the centerstand. Inside the seat tube was a serrated rod attached to a steel bar. 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. The stands had a habit of self-deploying while underway, and many owners quickly removed them!

Under Hopwood

So when Bert Hopwood arrived at BSA from Norton in early 1949, he inherited a successful 500cc bike in the A7, with instructions to turn it into an equally competent 650 — and to do it before Triumph launched their 650 Thunderbird. The race was on!

Though Hopwood’s A10 followed the same general layout and features of the earlier A7, almost none of the components were interchangeable. (Hopwood’s own 500cc twin, a scaled down version of the A10, appeared in 1951.) An important feature for Hopwood was the single camshaft layout, with the cam behind the crank. Pushrods buried in a tunnel in the cylinder block operated both the intake and exhaust rockers, with no pushrod tubes at the front of the engine to interfere with airflow. (Cooling for the cast iron cylinder head and barrels needed careful consideration.) But the main changes were to the cylinder head design, which used a narrower included valve angle, and separate oil wells for the exhaust valves to improve cooling, as well as a roller bearing replacing the drive-side ball race.

In the A10, a pair of half-time gears drove the camshaft and the magneto, with chain drive to the front mounted DC generator, just like the A7. Many of Hopwood’s efforts were also aimed at reducing mechanical noise with revised gear forms and quieting ramps on the cams. The A7 clutch and gearbox were retained with detail improvements.

The A10 was launched for 1950 with the 35 horsepower 650cc engine mounted in a “plunger” rear-suspension frame with around 2 inches of travel, though a “hardtail” frame was an option. A clever feature was a quickly detachable rear wheel — useful in those dark days of frequent punctures — and BSA’s patented “crinkle” hub, which allowed the use of equal-length straight spokes. The front brake was soon upgraded to 8-inches.

A 1950 test reported a top speed of 104mph for the new 650, which also proved capable of maintaining high speeds indefinitely. Properly maintained, the new engine could also last many miles between teardowns. And while the timing side crankshaft bush was often the object of concern, it typically lasted much longer than the main bearings on a Triumph 650 (according to Steve Wilson in his book BSA Motorcycles since 1950). That the A10 was conceived and designed as a 650 and not a stretched 500 may have helped.

For 1953, the headlight was covered with a pressed steel cowling that also carried the speedometer. And a tuned version of the A10, the 42 horsepower Super Flash was exported to the U.S. with an Amal TT carb — but still in the plunger frame. A new all-welded pivoted fork frame (based on the Gold Star item) arrived for 1954 with the swingarm mounted on Silentbloc bushings and Girling adjustable coil spring/damper units. At the same time, the semi-unit transmission was fully separated from the engine, meaning the slipper tensioner was dropped.

In 1956, the Super Flash was replaced by the swinging-fork A10 Road Rocket fitted with an alloy cylinder head and TT9 carburetor — and good for 109mph. New full width alloy brake drums were fitted (8-inch front for 1958). A stronger crank and larger big end bearings were fitted for 1958 (engine and frame number prefix DA-) allowing an increase to 43 horsepower for the sport model, which was renamed Super Rocket.

But the basic A10 soldiered on: the clutch went from six plates to five and then to four; the front brake went from 8-inch iron, to 7-inch alloy and back to 8-inch; but the base A10 never got an alloy cylinder head or dual carburetors. The A10 Flash enjoyed a production run of 12 years until it was replaced by the unit-construction A65 twin in 1962.

Lyle Whitter’s 1960 BSA A10 Golden Flash “Old Blue”

Though the A10 was always the “Golden Flash,” and its polychromatic beige finish was always available as an option, Lyle Whitter’s “Old Blue” is finished in the correct Nutley Blue for 1960.

Whitter’s father had been a motorcycle instructor in the Army during World War II and didn’t want his son to have any part of riding. That just made Whitter want to ride even more.

“My introduction to riding was a 1956 Panther 250 which a family friend owned.”

This first ride really got him enthused, but it was a 1959 Triumph TR6 that a family friend loaned him to ride to school that ignited his passion.

“I picked the bike up at his place a few blocks away and returned it on the way home. Father found out and was not happy at all especially after he tried the bike. Too much power, he said.”

About this time a cousin had a 1951 Gold Star for sale. After much pleading, the purchase was allowed — because “a 500cc single couldn’t hurt me too much …”

A hiatus in Whitter’s riding career lasted 25 years until a visit to the Classic & Vintage Swap Meet in Cloverdale, B.C. (classicbikeswapmeet.com). He resolved to get a British bike.

“I mentioned this to some fellow workers at the shipyard and asked if anybody knew of a British bike hidden away. Someone did.”

He told Whitter about a lady rider who was selling a BSA Golden Flash. She had bought a 1960 A10 new from Fred Deeley Imports in Vancouver and maintained it herself.

“She bought the 650 because it was easier to start than the 350 single BSA she owned before,” says Whitter.

In 1972 she decided it was time to put it away in her basement, because, she said, she lived too close to work and the bike didn’t even get warm on her commute, so bought a bicycle instead! She told Whitter she had traveled at least 225,000 miles by motorcycle since 1951, including riding a 250 across Canada in 1952, and to California and back.

Around 1990, she moved the A10 from her basement to a carport, where it was rapidly deteriorating when Whitter first saw it. Under a tarp was “… the ugliest, greasiest dull looking specimen of a motorcycle I had ever seen,” says Whitter. “It was covered completely with WD40. The mufflers were rusted through, and a horrible looking windshield was clipped on the handlebars. But it was complete and had 51,000 original miles on it.”

Some negotiation followed before a deal was done.

“It hadn’t been running since it had been put in the carport nine years before,” says Whitter. “It had only been started once in the previous 10 years.”
Whitter cleaned the magneto high tension pickups as well as cleaning and resetting the points. With fresh gas and spark plugs, “three kicks later and it was running, spraying rust and carbon all over the driveway!”

And while Old Blue is not “restored,” it did get a thorough makeover, starting with new tires and mufflers. Leaking battery acid had stripped paint from the frame, so that was repainted with two-pack. All other parts finished in black were repainted, and chrome parts re-plated. Whitter stripped the engine and rebuilt it with a new timing side bushing. Almost all other parts were re-used. “The new bearings and bushing were not needed,” says Whitter. “It was like new inside. Exactly the same clearance old and new.”

Other major items — seat, gas tank, side panels, fenders, headers — were re-used as found to retain their patina. That was 20 years ago now, but Old Blue still looks as good as “new.” How does Whitter like riding the Flash?

“Absolutely a delightful bike. Wonderful to ride. Handling is phenomenal. At that time, it probably beat most bikes as far as riding goes except for maybe Norton featherbed.”

Whitter’s only gripes about the A10 are the clutch (“horrible,” he says). BSA finally installed the Triumph 4-spring unit from late-1960 on. And while the rear brake is weak, the 8-inch SLS front stopper is “excellent.”

Wet sumping can also be a nuisance, says Whitter.

“It just hasn’t been ridden enough lately,” he says, though he has done at least 10,000 miles since the rebuild. Whitter also points to the A10’s legendary reliability:

“It’s acted up. Yes. But it’s never let me down on the side of the road.” MC

Men Without Shirts: Serious Speed in Skivvies

A rider doing 150 miles per hour 70 years ago at Bonneville riding a British bike and wearing not much more than a birthday suit? Rollie Free on the Vincent Black Lightning, right?

Certainly, Rollie Free did famously take the U.S. national motorcycle speed record in 1948, balanced on the rear fender of a Vincent Black Lightning wearing only a Speedo, shower cap and sneakers. But the above description fits at least one other speed record run.

Three years later, a softly-spoken, self-effacing racer from Eugene, Oregon, lined up a couple of very special BSAs on the salt flats for some equally outrageous speed attempts. His name: Gene Thiessen. The bikes were tuned versions of BSA’s new OHV parallel twins, first seen in road-going form the previous year: the 500cc A7 and 650cc A10. Though BSA officially disdained racing, the factory maintained a competition shop and made performance parts available to privateers. Newly appointed U.S. west-coast distributor Hap Alzina was keen to promote his business, and arranged for the special 650cc bike to be supplied. The 500cc A7 was Thiessen’s own race bike.

Alzina planned to challenge the AMA Class “C” (OHV 500cc, max 8:1 compression, gas fuel) and 650cc class “A” (any fuel, any compression) records. Thiessen removed the seat for the record attempt, spreading his weight over the rearset footpegs, handlebars, and rear fender. His clothing consisted of just a pair of tights, cloth aviator helmet and basketball shoes. His two runs on the 500 set a new class C record at an average of 123.69mph.

And so to the 650. To run class A, the iron engine was modified for alcohol fuel with 14.5:1 compression and a special twin port iron head fitted with two 1-inch Amal TT carbs. Previous runs at Rosamond Dry Lakes had shown that with 15:1 compression on alcohol, the pistons would start hitting the cylinder head near the 6,200rpm redline, so 14.5:1 pistons were used at Bonneville.

The first run was fast. By the tachometer and his gearing tables, Thiessen knew it was more than 150mph, and the timing confirmed that. But the price was a broken rocker oil feed. With only 30 minutes allowed between runs, a repair was hastily effected, and with some nitromethane added to the fuel (he claims this was the first time nitro had been used as an additive at Bonneville), Thiessen set off for the return trip. Again he was running well over 150mph, until, with ¼ mile to go, the engine seized. Thiessen grabbed the clutch and coasted the last 400 yards — yet still recorded a two-way average of 143.54mph, a new Class A record.