1952 BSA A7
Pre-Unit 500 Twin

1952 BSA A7 BACKGROUND
Like everyone else in the British motorcycle industry, BSA was caught flat-footed when Triumph introduced its game-changing 500 Speed Twin in 1938. And like virtually everyone else, BSA was relying heavily on single-cylinder designs for its bread and butter. But the new twins had arrived and suddenly everyone had to have one, as nearly every British marque struggled to bring its own vertical twin to market. World War II put all of that on hold, and it wasn’t until 1946 that civilian motorcycle production got going again, but when it did, it was a whole new ballgame. Of the other major British marques, BSA was one of the first to market with their own 500 vertical twin, the 1946 BSA A7.

1952 BSA A7 DESIGN
While early A7s used the old tried-and-true rigid frame, it was changed to a new frame featuring plunger rear suspension in 1949, with telescopic front forks. The engine was a vertical twin with cast iron cylinder block and removable head, with cast aluminum rocker box. The single camshaft set in the vertically-split crankcases behind the cylinder, and operating long pushrods that passed through a central tunnel in the cylinder block. They had lots of head bolts and studs, many extremely hard to reach, and they were prone to oil leaks. At its launch, the A7 displaced 495cc, but early teething problems led to a redesign in 1950, the new revised engine now displacing 497cc. They made 28 horsepower and were capable of hitting speeds of 85 mph, impressive for the day. While the engine/gearbox package was technically a non-unit setup, the duplex primary chain was adjusted by means of a slipper tensioner, rather than the (at the time) conventional manner of moving the gearbox in its mounts to tighten the primary chain, which also loosened the final drive chain, which then also had to be adjusted. The new system made for a neater, more compact package and was referred to as ‘semi-unit construction’.


1952 BSA A7 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

497cc

66mm X 72.6mm

7.2:1

1- Amal

3/8" duplex chain

Multi-plate, wet

5/8" X 3/8" chain

BSA constant-mesh 4-speed, foot shift


12.9:1

8.8:1

6.05:1

5.0:1

54.25"

30", unladen

4.5", unladen

3.25" x 19"

3.50" x 19"

3.5 gal

423 lbs


16.8 sec @ 84 mph

92 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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