BSA A65-A50

28 Мар 2015 | Author: | Комментарии к записи BSA A65-A50 отключены
BSA A 50 Royal Star

BSA A65-A50

Unit-Construction Twins


The BSA twins, the A65 being a 650 twin smaller sister-bike the BSA A10 500 twin, the natural result of the trend, sweeping the British motorcycle to unitize engine construction. most engine packages made up of separate crankcase, case gearbox, all bolted in mounting plates inside the

Known then as Non-Unit now as Pre-Unit, it had evolved from the days of the motorcycle industry, it was common for a motorcycle company to engines gearboxes from firms adapt them to cycles. But, by the late the major makers were all their own standardized components the was made to make engines more compact, stronger (in theory, allowing more with less vibration cheaper to produce.

Hence which placed all 3 component in one common set of cases. Triumph was one of the leaders in this area, first their 350cc 3T over to unit construction in followed by their 500cc 5T The handwriting was on the wall: it was only a of time before they their 650 twin over as (this would take in 1963).

It was clearly time for BSA to take their successful of vertical twins, the 500cc BSA A7 the BSA A10. Both used the design that was launched in 1947 with the original BSA A7 iron twin. So, work was in earnest to develope a Unit-Construction for their venerable line of Twins.

These would the BSA A65-A50 line.

Pre-Unit BSA A7 A10) LEFT. Unit-Construction BSA A65-A50) RIGHT.


The late 1950’s were a of great change in the British industry, everyone scrambling for hoping to come up with Next Big Thing’. Triumph had it twice, with both the TR6 Norton had its Featherbed. And BSA had the Gold

The 50’s had been good to the but their was a change in the wind, a heading their way. One trend that emerged the turmoil was enclosing smoothing to make them more You only have to look at a Triumph, a Vincent Black or a Velocette Vogue you’ll get the

For whatever reason, it would that BSA decided to apply same design logic to new engine. They took was an elegantly sculptured engine was very pleasing to the eye, and it into a shapeless blob had no visual appeal whatsoever. called it The Power Egg. The Egg?

The Power Egg. Go The problem here is that, you can quickly restyle a bike trends fade, an engine easy, or cheap to change, in overall shape.

The enclosure fad within a few years, never on in the US at all all those enclosed bikes from the marketplace. But the BSA A65-A50 Egg was still with us would be, unchanged, until BSA’s in 1972.

1966 BSA A65 Hornet 650 had pipes for off-road work. The BSA made a pretty decent racer, back in the day.


The basic internal design of the BSA engine actually changed little in the transition. The layout was the 360-degree one-piece crank alloy conrods, single cam the cylinder block driven by a chain on the right side, chain clutch on the right the same basic gearbox. All of was tucked into a new set of unitized cases.

These alloy were split vertically the centerline, with the inner chaincase as part of the left half, the gearbox housing of the right. The two engines, the 500cc A50 the A65, shared most in common, including their at 74mm. The A65’s bore was for a displacement of 654cc, and an nearly-square

The A50’s bore was 65.5mm for Both came out with carburetors alloy heads.

BSA 1967 BSA A65 Spitfire Mark


BSA A65-A10 names during the unit era were many. The 500cc BSA A50 in a variety of styles names, Star, Royal Star, Wasp. The 650cc BSA A65 carried names like Rocket, Thunderbolt Rocket, Lightning, Rocket, Lightning Clubman, Hornet, Spitfire Hornet Scrambler.

But no matter how BSA dressed up, these new unit-construction twins sold as well, or garnered the respect as was accorded to the pre-unit they replaced. They to lack the character that the A7 A10 had in


It’s to say what caused BSA Motorcycles to so many missteps in this era. While it didn’t like much didn’t very well, the unit-construction BSA were actually pretty engines. The BSA A65-A50 had their but these were slowly, being remedied in the normal development process used by motorcycle makers of the day.

Weaknesses included an alloy oil (instead of cast iron) would warp thus to deliver enough pressure, a that delivered oil to the big ends via the (right) side main through the crank, leading to an left big end bearing. At high the already weak oil pump was to pump oil into the center of the working against centrifugal

To make matters worse, in BSA replaced the drive (left) caged ball main to a roller race. This the positive location of the crankshaft, it to wander from side to quickly wearing out the flimsy thrust washer intended to with the situation. This lead to a spun timing main bush, cutting off the oil to the crankshaft completely, breaking the or conrods shattering the cases.

has been solved today modern-day solutions, but the BSA factory seemed to get it quite right.

BSA A65 Thunderbolt, the last BSA A65-A50 the dreaded Oil-in-Frame bikes


In a strike of stupidity, BSA Motorcycles took entire twin line BSA A65-A50) Triumph’s very 650 twin line as well in reintroduced both marques’ big with completely new oil-bearing cycle gear. This was an on the part of BSA Motorcycles, the owner of Motorcycles, to modernize its product unitize as many parts as between the two brands.

The new frames gear were shared in between the BSA A65-A50, and the Triumph TR6 650’s. A product of another of horrendous follies, their overrated ‘technology center’ Hall, the new Oil-in-Frame machines late had major problems had to be overcome before production begin, which was delayed months. It was found very in the process, that the Triumph couldn’t be fitted into the new in one piece.

The solution: remove the rocker from the fully-assembled engines, the engines into the frames, reinstall the rocker boxes. this required completely rocker boxes head This was the kind of foolishness had overcome BSA Motorcycles at the time.

things like a 34-1/2 seat height, flimsy headlight brackets cheesy just went to show how they were at the time. all this, the new 1971 BSA A65-A50 was a machine.

1971 BSA A65 Thunderbolt, the year for Oil-in-Frame. 1972 out to be the last year for the BSA A65-A50, in the last year for all BSA Motorcycles.


You have to hand it to them. were trying. The 1971 of the BSA Triumph twins was a bold move that, done could have made a difference in the fortunes of the two marques. But it handled as badly as everything seemed to be doing at the time. It was too took too long, it was too slow too from what their fans were expecting.

combined, the entire move to for both BSA Triumph was a complete It took so long to get them to that very few bikes sold the first year. The reaction was mixed, but certainly not about the new look.

The new BSA A65-A50 never sold as well as the bikes they

A classic BSA A65-A50: a 1971 BSA A65 Scrambler, with high


BSA had in serious financial trouble the 1960’s, despite phenomenal in Triumphs. Backroom political (former Ariel owner Sangster, now a BSA board member, was the company of its assets selling off cheap to improve the short-term line) had gutted this industrial giant.

BSA A 50 Royal Star

What they had left they on …-end projects like Hall, the BSA 350 Fury, scooters a badly-designed oil-bearing frame no one asked for. All of this of bad management to go with it, swamped the by 1972. Few 1972 BSA A65-A50 were built. Small stopped producing BSA’s to on building Triumph Tridents.

BSA was no more, the end of a long line of motorcycles amazing history.



654cc OHV Vertical

First year for the Unit-Construction the 654cc A65 the 499cc A50. were virtually identical than bore front diameter. BSA debuts its new design which it dubs the Power

New frame much new cycle

654cc OHV Vertical Twin

year for the new unit-construction twins. carryover from 1963 year. The last of the venerable A10 650 twins, the Rocket Gold ends production.

Unfortunately, the new A65 achieved nearly the success of its ancestors.

654cc OHV Vertical Twin

unit-construction 650 twin soldiers on, to gain traction in a fast-changing

654cc OHV Vertical Twin

big unit-construction 650 twin continues on minor, evolutionary changes and there. With Honda starting to gobble up serious share, BSA should be scrambling to up with something new. is the only British brand is still doing well, and doing great. for a while anyway.

654cc OHV Vertical

The BSA 650 twin, available in a variety of similar models, struggles to traction in the fast-changing marketplace. of the earlier design flaws been worked out by now, so the BSA A65 is turning out to be a pretty darned motorcycle, however hopelessly by Honda .

A more complete breakdown of the BSA A65-A50 is coming We’re adding content Thank you for your patience.

keep checking back, as site continues to grow the world’s greatest website Classic British Motorcycles.




BSA A 50 Royal Star
BSA A 50 Royal Star
BSA A 50 Royal Star
BSA A 50 Royal Star
BSA A 50 Royal Star


Other articles of the category "BSA":

Our partners
Follow us
Contact us
Our contacts

Born in the USSR


About this site

For all questions about advertising, please contact listed on the site.

Motorcycles catalog with specifications, pictures, ratings, reviews and discusssions about Motorcycles.