1955 BSA A7
Pre-Unit 500 Twin

1955 BSA A7 BACKGROUND
The 500cc A7 was BSA's first vertical twin and marked its entry into that very lucrative market, started by the Triumph Speed Twin just prior to the war. At war's end, virtually every British motorcycle manufacturer fielded their own vertical twin, usually starting out at around 500cc. That's exactly what BSA did, launching the 500cc A7 twins in 1946. It was a strong-seller from the start and was continually improved and developed, gaining rear suspension in 1953. By 1950, BSA followed Triumph's lead and punched their 500cc A7 out to 650cc, giving it the model designation A10. At this point, the A7 became BSA's entry-level twin, and there it remained for the rest of its career, until it, and the A10 were replaced by their unit-construction descendants, the 500cc A50 and the 650cc A65 in 1962.

THE BASIC LAYOUT OF THE 1955 BSA A7
The engines never changed their basic design from their inception in 1946 through their replacement by the A50 in 1962. It was basically an air-cooled vertical twin, with both pistons rising and falling together on a 360-degree crankshaft riding on two main bearings (bushings on the timing side in the early bikes). The single cam lived behind the cylinder with its pushrods passing through a tunnel cast into the cylinder block. The timing gear along with the magneto drive are on the right side, with the primary chain and clutch on the right. The clutch is hand-operated, and the 4-speed constant-mesh gearbox is shifted with the right foot (the way God intended). All of this is of non-unit construction (crankcase, primary chain case and gearbox all are separate components bolted together with brackets). It was fed by a single Amal carburetor. The frames and running gear were state-of-the-art for 1955, with swing-arm rear suspension, telescopic front forks with hydraulic damping, and 7-inch single-leading shoe (SLS) brakes front and rear. Overall the 1955 BSA A7 was a very competent machine, capable of keeping up with modern traffic and providing years of reliable service. This was indeed BSA's Golden Age and the 1955 BSA A7 was a bona fide hit for them.


1955 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

1/2" X .305" chain

Multi-plate, wet

5/8" X 3/8" chain

BSA constant-mesh 4-speed, foot shift


13.6:1

9.0:1

6.38:1

5.28:1

54.25"

30", unladen

4.5", unladen

3.25" x 19"

3.50" x 19"

4.0 gal

416 lbs


15.7 sec @ 77 mph

84.5 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 Motorcycles: The Final Evolution



The BSA Gold Star: Motorcycle History



Illustrated Bsa Buyer's Guide (Motorbooks International Illustrated Buyer's Guide)



Bsa Twin Restoration



BSA Unit Singles: The Complete Story including the Triumph Derivatives



Bsa Motor Cycles: Since 1950 (British Motor cycles since 1950)



BSA Unit Twins



BSA 500 & 650 Twins: The Essential Buyer's Guide



Triumph and Bsa Triples



How to Restore Triumph Trident T150/T160 & BSA Rocket III: YOUR step-by-step colour illustrated guide to complete restoration (Enthusiast's Restoration Manual)




For more like these, visit our BSA BOOK STORE






Please visit our
MOTORCYCLE BOOK STORE


Take a tour of our site...

HOME PAGE
Triumph Motorcycles
.....Bonneville
.....Tiger
.....Trophy
.....TR6
.....TR7
.....Trident
.....X-75 Hurricane
.....6T Thunderbird
.....5T Speed Twin
.....Daytona
.....Twenty-One
.....3T 350 Twins
BSA Motorcycles
.....A65
.....A10
.....A7
.....Gold Star
.....Bantam
.....Rocket 3
.....B50
Norton Motorcycles
.....Commando
.....Atlas
.....Dominator
.....Model 7
.....Manx
.....Navigator
AMC-Associated Motor Cycles
Matchless-AJS Motorcycles
.....G3
.....G9
.....G12
.....G80
Royal Enfield Motorcycles
.....Interceptor
.....Bullet
Ariel Motorcycles
.....Square Four
.....Red Hunter
.....Cyclone
Vincent Motorcycles
.....Black Shadow
.....Rapide
.....Comet
.....Egli-Vincent
Velocette Motorcycles
.....KSS
.....KTT
.....LE
.....MAC
.....Thruxton
.....Venom
.....LE
Rickman Motorcycles
Japanese Motorcycles
.....Honda
.....Kawasaki
.....Suzuki
.....Yamaha
Cafe Racers
....Triumph Cafe Racers
.....Norton Cafe Racers
.....Other Cafe Racers
Choppers & Bobbers
.....Choppers
.....Triumph Choppers
.....BSA Choppers
.....Rat Bikes
Classic Racing Motorcycles

Classic Motorcycle Events
.....Auctions
.....Shows
.....Rides
Classic Motorcycle Restoration
Classic Motorcycle Shops
Classic Motorcycle Clubs
Send us Pictures of YOUR BIKE
YOUR BIKE Pictures

HOME PAGE
.....About Us
.....Site Map
.....CONTACT US
.....Please visit our BLOG
.....Subscribe to our FREE e-zine BRIT IRON
.....BRIT IRON E-zine Back Issues

Visit our STORES
.....Motorcycle Books
.....Motorcycle Magazines
.....Motorcycle Calendars
.....Motorcycle Accessories
..........Motorcycle Helmets
..........Motorcycle Rain Suits
..........Motorcycle Locks & Security
..........Motorcycle T-Shirts
..........Motorcycle Diecast Models
..........GoPro Cameras
.....Motorcycle Parts
..........Motorcycle Tires
..........Motorcycle Chains
..........Motorcycle Batteries
..........Motorcycle Handlebars
.....Motorcycle Tools
..........Whitworth Tools
..........Tire Tools
..........Chain Tools

Crazy about cars, too? Check out our sister site:
www.American-Muscle-Cars.net

Back to top - 1955 BSA A7
11/21/17

Learn how to BUILD YOUR OWN WEBSITE, like I did.

BREAKING NEWS:

The New BSAs?
Insider tells all



Las Vegas Auction Week
Almost 2,000 bikes!



NEW PAGE:
Vintage Motorcycle Pictures



2018 CALENDARS ARE HERE!



Visit our new
Motorcycle Store

FLAT TIRE ON A RIDE?
Emergency Tire Repair Kit





Please visit our
MOTORCYCLE BOOK STORE


Subscribe to your favorite
MOTORCYCLE MAGAZINES





BIKES FOR SALE!
Check out our
FREE
Classifed Ads



NEW SECTIONS:

Military
Motorcycles

Brough Superior

NEW PAGES
added this month:

* 1933 BSA B33
* John's British Cycles
* 1961 Matchless G80 Typhoon
* 1958 BSA Gold Star
* Ariel Twins
* 1959 Ariel Huntmaster
* 1964 Triumph Thunderbird
* 1961 Triumph Cub
* 1959 Velocette Venom
* 1956 Triumph TR5R
* 1955 Vincent Black Prince
* 1951 Triumph Speed Twin
* 1958 Ariel Huntmaster
* 1954 Triumph T15 Terrier
* Military Motorcycles
* 1941 Harley-Davidson WLA
* 1942 Harley-Davidson WLA
* 1999 Harley-Davidson MT500
* 1957 Matchless G11
* 1955 Ariel Red Hunter
* 1953 BSA Gold Star
* 1951 BSA Gold Star
* 1949 Vincent Rapide
* 1949 Vincent Comet
* 1939 BSA Silver Star
* 1947 Mathcless G80
* 1962 Norton Dominator 88
* 1981 Rickman-Kawasaki CR900
* Brough Superior Motorcycles
* 1939 Brough Superior SS100
* 1939 Brough Superior SS80
* 1938 Brough Superior SS100
* 1935 Brough Superior
* 1926 Brough Superior SS80
* Rio Vista-Delta Ride 2018
* 1942 BSA M20
* 1971 BSA A70 Lightning
* 2014 Royal Enfield Continental GT
* 2012 Triumph Bonneville
* 2010 Triumph Bonneville
* 1955 Matchless G45
* 2007 Royal Enfield Bullet
* 2009 Triumph Bonneville 50th Anniversary
* 1941 Matchless G3
Enjoy. More coming soon...