1954 BSA A10
Pre-Unit 650 Twin


1954 BSA A10 Golden Flash

1954 BSA A10 BACKGROUND
Like every other British motorcycle manufacturer at the time, BSA was following Triumph’s lead in the parallel twin race. Triumph introduced the first parallel twin, the 500 Speed Twin in 1938, but World War II intervened, curtailing all civilian production. It wasn’t until 1946 that the rest of the industry started catching up. BSA hit the market with their own 500 twin, the A7. But Triumph quickly upped the ante, punching their own 500 out to 650cc with their new 1950 Thunderbird. Of course BSA had to counter, and counter they did, with their own 650 twin, (also an expansion of their existing 500 twin), the 1950 A10.
1954 BSA A10 ENGINE DESIGN
The engine was fairly conventional and closely followed the A7s architecture. The A7 had already been well-proven, so many typical teething problems inherent in anew design could be avoided. So, like the 500 A7, the new 650 A10 had vertically-split aluminum crankcases arranged in non-unit fashion with a typical 4-speed gearbox. However, they called is ‘semi-unit’ because instead of the usual non-unit construction method of moving the gearbox back and forth to affect primary chain tension, the A10 used a slipper tensioner within the primary chaincase to adjust the chain. This made for a much more rigid structure and greatly simplified the process. The A10 had a cast iron cylinder block and removable cylinder head with a revised allow rocker box up top. The head had an integral intake manifold that accommodated its single Amal carburetor. There was a single camshaft behind the cylinders with the pushrods running through a central tunnel integral to the cylinder block. It was a powerful machine in its day, easily capable of 100 mph top speed, and could run the quarter mile in 16 seconds (laughable today, but impressive in 1951).
1954 BSA A10 FRAME & RUNNING GEAR
The 1954 BSA A10 was the first year to benefit from a new frame with swing-arm rear suspension, replacing the old plunger-type. The front suspension was via telescopic forks with hydraulic damping. They had a hinged rear fender to aid in tire changes. As with the engine, much of the running gear was carried over from the 500cc A7 line, and so proved to be robust and reliable. 1954 was also the first year for a new BSA A10, the twin-carb 650 Road Rocket.
1954 BSA A10 GOLDEN FLASH
From its launch in 1950, the BSA A10 came standard in a black and chrome color scheme. But as an option, they offered a very distinctive gold-over-chrome with red pinstriping theme that gave the BSA A10 Golden Flash its name. They were otherwise mechanically identical to the standard black-and-chrome A10s. Staring in 1954, the A10 Golden Flash became the entry-level 650, with the new twin-carb, higher-performance 1954 BSA A10 Road Rocket now occupying the top tier of the A10 hierarchy.

1954 BSA A10 SPECIFICATIONS

Engine type

Displacement

Bore & Stroke

Compression

Carburetor

Primary drive

Clutch

Final drive

Gearbox

Ratios, overall:

1st, Bottom

2nd

3rd

4th, Top

Wheelbase

Seat height

Ground clearance

Tires, front

Tires, rear

Fuel capacity

Curb weight

PERFORMANCE

1/4 mile

Top speed

Air-cooled OHV vertical twin

646cc

70mm X 84mm

6.5:1

1- Amal

1/2" X.305 single-row chain

Multi-plate, wet

5/8" X 3/8" chain

BSA constant-mesh 4-speed, foot shift


11.67:1

7.95:1

5.47:1

4.52:1

56.5"

31", unladen

5.0", unladen

3.25" x 19"

3.50" x 19"

4.25 gal

443 lbs


16.0 sec @ 80 mph

100 mph



MORE BSA PAGES:
BSA Motorcycles
..... BSA Gold Star
..........1939
..........1953
..........1954
..........1961
..........1962
..... BSA A7 (pre-unit 500)
..........1952
..........1955
..... BSA A10 (pre-unit 650)
..........1951
..........1954
..........1957
..........1958
..... BSA A65 (unit-construction 650)
..........1962
..........1963
..........1964
..........1965
..........1966
..........1967
..........1968
..........1969
..........1970
..........1971
..... BSA Rocket 3 (750 triple)
..........1969
..........1971
..... BSA Bantam


Check out these BSA BOOKS

BSA - THE COMPLETE STORY


BSA MOTORCYCLES: THE FINAL EVOLUTION


HISTORY OF BSA MOTORCYCLES


BSA: ILLUSTRATED MOTORCYCLE LEGENDS, by Roy Bacon


HOW TO RESTORE YOUR BSA ROCKET 3 & TRIDENT


CHILTON’S BSA MOTORCYCLE REPAIR & TUNE-UP GUIDE


BSA SINGLES 1945-1963 GOLD PORTFOLIO


BSA SINGLES 1964-1974 GOLD PORTFOLIO


BOOK OF THE BSA - OWNERS SHOP MA NUAL, PRE-WAR


BSA 350, 441 & 500 SINGLES, UNIT CONSTRUCTION 1958-1973


BSA CLASSIC MOTORCYCLES


BSA & TRIUMPH TRIPLES: GOLD PORTFOLIO 1968-1976


BSA UNIT SINGLES: COMPLETE STORY


BSA A7 & A10 TWINS, 1957-1962, by Haynes


BSA A50 & A65 TWINS: ALL MODELS


ILLUSTRATED HISTORY OF BSA MOTORCYCLES


BSA TWINS A7 & A10 1946-1962, GOLD PORTFOLIO


THE BSA GOLD STAR


MAINTENANCE MANUAL FOR BSA M20


SECOND BOOK OF THE BSA 500 & 650 TWIN 1962-1969


BSA PRE-UNIT SINGLES WORKSHOP MANUAL, by Haynes


TRIUMPH TRIDENT & BSA ROCKET 3 WORKSHOP MANUAL, by Haynes


BSA BANTAM WORKSHOP MANUAL 1948-1971, by Haynes


BSA UNIT TWINS, THE COMPLETE STORY


BOOK OF BSA SINGLES & V-TWINS 1936-1952


RUPERT RATIO UNIT SINGLE ENGINE MANUAL, BSA & TRIUMPH


RUPER RATIO, EVERYTHING BUT THE ENGINE, BSA & TRIUMPH


BSA A50 & A65 TWINS 1962-1973, Haynes Workshop Manual


BSA GOLD STAR & OTHER SINGLES, by Roy Bacon


BSA MOTORCYCLES SINCE 1950,BR>

BSA UNIT SINGLES OWNERS WORKSHOP MANUAL #127, 1958-1972, by Haynes


BSA TWINS 150 & 165 GOLD PORTFOLIO, by RM Clarke


ILLUSTRATED BSA BUYER’S GUIDE, by Roy Bacon


BSA BANTAM, by Owen Wright


BSA PRE-UNIT TWINS, by Mick Walker


BOOK OF THE BSA OHV & SV SINGLES - 250cc 1954-1970


BSA TWINS & TRIPLES, by Roy Bacon


TRIUMPH & BSA TRIPLES: THE COMPLETE STORY


BOOK OF BSA TWINS, ALL 500 & 650 1948-1962, by Floyd Clymer


BOOK OF THE BSA OHV & SV SINGLES 1945-1954: 250, 350, 500 & 600


BSA BANTAM BIBLE, ALL MODELS 1948-1971


WHERE BSAs DARE: BSA’s 1952 ISDT GOLDS & MAUDES TROPHY


ILLUSTRATED MOTORCYCLE LEGENDS: BSA, by Roy Bacon


BSA BANTAM ESSENTIAL BUYER’S GUIDE


BOOK OF THE BSA BANTAM


BSA 500 & 650 UNIT TWINS, Clymer Repair Manual


BSA COMPETITION HISTORY


BSA MOTOR CYCLING ANNUAL, 1937, Kindle






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1954 BSA A10
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