BSA A65-A50: THE MOVE TO UNIT CONSTRUCTION
The BSA A65-A50 twins, the A65 being a 650 twin & it's smaller sister-bike the BSA A10 500 twin, were the natural result of the trend, then sweeping the British motorcycle industry, to unitize engine construction. Prior, most engine packages were made up of separate crankcase, primary case & gearbox, all bolted together in mounting plates inside the frame. Known then as Non-Unit construction, now as Pre-Unit, it had evolved from the earliest days of the motorcycle industry, when it was common for a motorcycle company to outsource engines & gearboxes from other firms & adapt them to their cycles. But, by the late 1950's the major makers were all using their own standardized components & the move was made to make engines lighter, more compact, stronger structurally (in theory, allowing more power with less vibration & flexing) & cheaper to produce. Hence Unit-Construction, which placed all 3 component sets in one common set of cases. Triumph Motorcycles was one of the leaders in this area, converting first their 350cc 3T twin over to unit construction in 1957, followed by their 500cc 5T twin. The handwriting was on the wall: it was only a matter of time before they converted their 650 twin over as well (this would take place in 1963). It was clearly time for BSA Motorcycles to take their successful line of vertical twins, the 500cc BSA A7 & the 650cc BSA A10. Both used the same design that was launched back in 1947 with the original BSA A7 cast iron twin. So, work was begun in earnest to develope a Unit-Construction replacement for their venerable line of Pre-Unit Twins. These would become the BSA A65-A50 line.
Pre-Unit (1947-62 BSA A7 & A10) LEFT. Unit-Construction (1962-72 BSA A65-A50) RIGHT.
THE POWER EGG, WHAT A CONCEPT
The late 1950's were a time of great change in the British motorcycle industry, everyone scrambling for position, hoping to come up with 'The Next Big Thing'. Triumph had nailed it twice, with both the TR6 & Bonneville. Norton had its Featherbed. And BSA had the Gold Star. The 50's had been good to the Brits, but their was a change in the wind, a storm heading their way. One quirky trend that emerged from the turmoil was enclosing & smoothing motorcycles to make them more car-like. You only have to look at a Bathtub Triumph, a Vincent Black Prince, or a Velocette Vogue & you'll get the idea. For whatever reason, it would appear that BSA decided to apply this same design logic to their new engine. They took what was an elegantly sculptured engine that was very pleasing to the eye, and turned it into a shapeless blob that had no visual appeal whatsoever. They called it "The Power Egg". The Power Egg? The Power Egg. Go figure. The problem here is that, while you can quickly restyle a bike when trends fade, an engine isn't easy, or cheap to change, especially in overall shape. The enclosure fad faded within a few years, never catching on in the US at all & all those enclosed bikes vanished from the marketplace. But the BSA A65-A50 Power Egg was still with us & would be, relatively unchanged, until BSA's death in 1972.
1966 BSA A65 Hornet 650 had high pipes for off-road work. The BSA A65-A50 made a pretty decent desert racer, back in the day.
THE SAME, BUT DIFFERENT...
The basic internal design of the BSA A65-A50 engine actually changed very little in the transition. The layout was the same: 360-degree one-piece crank with alloy conrods, single cam behind the cylinder block driven by a gear chain on the right side, primary chain & clutch on the right with the same basic gearbox. All of this was tucked into a new set of unitized engine cases. These alloy cases were split vertically down the centerline, with the inner primary chaincase as part of the left crankcase half, & the gearbox housing part of the right. The two engines, the 500cc A50 & the 650cc A65, shared most parts in common, including their stroke, at 74mm. The A65's bore was 75mm for a displacement of 654cc, and an nearly-square ratio. The A50's bore was 65.5mm for 499cc. Both came out with single carburetors & alloy heads.
BSA A65-A50: 1967 BSA A65 Spitfire Mark III.
BSA A65-A10 model names during the unit construction era were many. The 500cc BSA A50 came in a variety of styles & names, including Star, Royal Star, Cyclone, & Wasp. The 650cc BSA A65 carried model names like Rocket, Thunderbolt, Thunderbolt Rocket, Lightning, Lightning Rocket, Lightning Clubman, Spitfire, Hornet, Spitfire Hornet & Firebird Scrambler. But no matter how BSA dressed them up, these new unit-construction twins never sold as well, or garnered the same respect as was accorded to the pre-unit bikes they replaced. They seemed to lack the character that the A7 & A10 had in spades.
FROM BAD TO WORSE
It's hard to say what caused BSA Motorcycles to make so many missteps in this crucial era. While it didn't look like much & didn't sell very well, the unit-construction BSA twins were actually pretty good engines. The BSA A65-A50 had their shortcomings, but these were slowly, methodically being remedied in the normal evolutionary development process used by British motorcycle makers of the day. Weaknesses included an alloy oil pump (instead of cast iron) that would warp & thus fail to deliver enough pressure, & a scheme that delivered oil to the big ends via the timing (right) side main bush & through the crank, leading to an under-oiled left big end bearing. At high rpms, the already weak oil pump was trying to pump oil into the center of the crank working against centrifugal force. To make matters worse, in 1966 BSA replaced the drive (left) side caged ball main bearing to a roller race. This removed the positive location of the crankshaft, allowing it to wander from side to side, quickly wearing out the flimsy shims & thrust washer intended to cope with the situation. This usually lead to a spun timing side main bush, cutting off the oil supply to the crankshaft completely, breaking the crankshaft or conrods & shattering the cases. This has been solved today with modern-day solutions, but the BSA factory never seemed to get it quite right.
1970 BSA A65 Thunderbolt, the last BSA A65-A50 before the dreaded "Oil-in-Frame" bikes appeared.
In a strike of particular stupidity, BSA Motorcycles took their entire twin line (the BSA A65-A50) & Triumph's very successful 650 twin line as well & in 1971 reintroduced both marques' big twins with completely new oil-bearing frames & cycle gear. This was an attempt on the part of BSA Motorcycles, the owner of Triumph Motorcycles, to modernize its product line & unitize as many parts as possible between the two brands. The new frames & cycle gear were shared in common between the BSA A65-A50, and the Triumph TR6 & Bonneville 650's. A product of another of BSA's horrendous follies, their overpriced & overrated 'technology center' Umberslade Hall, the new "Oil-in-Frame" machines arrived late & had major problems that had to be overcome before production could begin, which was delayed many months. It was found very late in the process, that the Triumph engines couldn't be fitted into the new frames in one piece. The solution: remove the rocker boxes from the fully-assembled engines, stuff the engines into the frames, then reinstall the rocker boxes. Even this required completely revised rocker boxes & head bolts. This was the kind of foolishness that had overcome BSA Motorcycles at the time. Other things like a 34-1/2 inch seat height, flimsy wire headlight brackets & cheesy controls just went to show how clueless they were at the time. Despite all this, the new 1971 BSA A65-A50 was a handsome machine.
1971 BSA A65 Thunderbolt, the first year for Oil-in-Frame. 1972 turned out to be the last year for the BSA A65-A50, in fact the last year for all BSA Motorcycles.
THE END IS NEAR
You have to hand it to them. They were trying. The 1971 makeover of the BSA & Triumph twins was a bold & ambitious move that, done right, could have made a real difference in the fortunes of the two marques. But alas, it handled as badly as everything they seemed to be doing at the time. It was too expensive, took too long, it was too slow & too different from what their devoted fans were expecting. Everything combined, the entire move to Oil-in-Frame for both BSA & Triumph was a complete fiasco. It took so long to get them to market that very few bikes were sold the first year. The market's reaction was mixed, but certainly not enthusiastic about the new look. The new BSA A65-A50 never sold nearly as well as the bikes they replaced.
A classic BSA A65-A50: a 1971 BSA A65 Firebird Scrambler, with high pipes.
BSA PASSES INTO HISTORY
BSA had been in serious financial trouble throughout the 1960's, despite phenomenal sales in Triumphs. Backroom political dealings (former Ariel owner Jack Sangster, now a BSA board member, was stripping the company of its assets & selling them off cheap to improve the short-term bottom line) had gutted this once-mighty industrial giant. What little they had left they squandered on dead-end projects like Umberslade Hall, the BSA 350 Fury, scooters & trikes & a badly-designed oil-bearing frame that no one asked for. All of this & lots of bad management to go with it, swamped the company by 1972. Few 1972 BSA A65-A50 machines were built. Small Heath stopped producing BSA's to concentrate on building Triumph Tridents. BSA Motorcycles was no more, the end of a long line of wonderful motorcycles & amazing history.
1965 BSA A65
654cc OHV Vertical Twin
First year for the Unit-Construction Twins, the 654cc A65 & the 499cc A50. They were virtually identical other than bore & front brake diameter. BSA debuts its new design language, which it dubs "the Power Egg". New frame & much new cycle gear.
1963 BSA A65
654cc OHV Vertical Twin
Second year for the new unit-construction twins. Mostly carryover from 1963 model year. The last of the venerable pre-unit A10 650 twins, the Rocket Gold Star, ends production. Unfortunately, the new A65 never achieved nearly the success of its pre-unit ancestors.
1964 BSA A65
654cc OHV Vertical Twin
Classic unit-construction 650 twin soldiers on, struggling to gain traction in a fast-changing marketplace.
1965 BSA A65
654cc OHV Vertical Twin
BSA's big unit-construction 650 twin continues on with minor, evolutionary changes here and there. With Honda
just starting to gobble up serious market share, BSA should be scrambling to come up with something new. Triumph
is the only British brand that is still doing well, and they're doing great...for a while longer, anyway.
1966 BDSA A65
654cc OHV Vertical Twin
The BSA 650 twin, available in a variety of surprisingly similar models, struggles to gain traction in the fast-changing marketplace. Many of the earlier design flaws have been worked out by now, so the BSA A65 is actually turning out to be a pretty darned good motorcycle, however hopelessly outclassed by Honda
A more complete year-by-year breakdown of the BSA A65-A50 is coming soon. We're adding content constantly. Thank you for your patience. Please keep checking back, as this site continues to grow into the world's greatest website about Classic British Motorcycles.
BSA TWINS, A50 & A65 GOLD PORTFOLIO
BSA TWINS, A7 & A10 GOLD PORTFOLIO
BSA UNIT SINGLES
BSA UNIT CONSTRUCTION TWINS: COMPLETE STORY
BSA UNIT TWINS
BOOK OF BSA OHV & SV SINGLES 1945-1954
BOOK OF BSA OHV & SV SINGLES 1954-70
BOOK OF BSA TWINS, 500 & 650 1948-62
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BSA BANTAM BIBLE
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