BSA A7
Encyclopedia
The BSA A7 was a British
motorcycle
manufactured by Birmingham Small Arms Company
(BSA) at their factory in Armoury Road, Small Heath
, Birmingham
in 1946. There were actually two versions of the A7, the original 495cc version and an improved 497cc version launched in 1950. Although its name was changed to the Star Twin and later the Shooting Star the BSA A7 continued in production with minor modifications until 1961.
, Herbert Parker and David Munro, the BSA A7 was the first of the BSA twin-cylinder
motorcycles and was ready for launch in 1939, but the outbreak of World War II
delayed the launch until September 1946 when hostilities ended. The very first A7 off the production line was flown to Paris
for the first motorcycle show after the end of the war. There was huge demand for affordable transport after the war and the simplicity of the A7 twin was helped along by the slogan 'It's time YOU had a BSA!'.
behind the cylinders operated the valve
s via long pushrods passing through a tunnel in the cast iron block. This system needed a considerable number of studs and nuts to fasten down the cylinder head
and rockerboxes, many of them deeply recessed and requiring well-made box spanners or the (then uncommon) sockets. As with other British motorcycles of the period, this kind of set-up regularly led to oil leaks.
Most motorcycles of this period tensioned the primary chain by drawing or rotating the gearbox backwards on a hinge with threaded rods, this was known as pre-unit construction
. The first A7 featured a fixed gearbox, bolted to the back of the crankcase
, and an internal tensioner for the duplex primary chain
. This gave it the appearance of unit construction and pioneered the system later used in unit-construction engines (e.g. BSA C12/C15, BSA B40, Triumph 3TA and on). However, in 1954 a re-design reverted to the older system. The electrics (as was universal for larger British motorcycles of the period) consisted of two independent systems, the very reliable and self-contained Lucas
magneto
, with a dynamo generator
to charge the battery and provide lights. Carburation
was a single Amal remote float Type 6 until 1955 when it was upgraded to a 376 Monobloc.
designed 650cc twin cylinder BSA A10
. Although resembling the A7 500cc twin, it had a revised engine design and a new A7 soon followed, based on the A10 - in response to competition from the Triumph Tiger 100
. Launched as the BSA Star Twin the new model featured twin carburettors and increased compression ratio
. It also had the latest design of cylinder head with austenitic steel inlet and exhaust valves. The uprated engine was fitted to a plunger frame and finished extra chrome. Both models were produced with an option of rigid or plunger frames until 1954 and the introduction of a pivoted fork frame. The new frame also led to a separate gearbox to replace the bolted on version.
and the International Six Days Trial
, achieving 4,500 miles without problems and confirming the reliability of the design. All three bikes were randomly selected from the production line, picked up Gold medals and earned BSA the Team award as well as the Trophy. The three bikes were ridden by Brian Martin, Fred Rist and Norman Vanhouse. From Birmingham the team rode to Vienna
then on through Germany
, Denmark
, Sweden
and Norway
before returning safely and with a clean sheet to Birmingham
.
fuel, which together with a compression ratio of 8 to 1 enabled rider Gene Thiessen to achieve a two way record speed of 123.69 mph.
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
motorcycle
Motorcycle
A motorcycle is a single-track, two-wheeled motor vehicle. Motorcycles vary considerably depending on the task for which they are designed, such as long distance travel, navigating congested urban traffic, cruising, sport and racing, or off-road conditions.Motorcycles are one of the most...
manufactured by Birmingham Small Arms Company
Birmingham Small Arms Company
This article is not about Gamo subsidiary BSA Guns Limited of Armoury Road, Small Heath, Birmingham B11 2PP or BSA Company or its successors....
(BSA) at their factory in Armoury Road, Small Heath
Small Heath, Birmingham
Small Heath is an inner-city area within the city of Birmingham, West Midlands, England. It is situated on and around the A45 ....
, Birmingham
Birmingham
Birmingham is a city and metropolitan borough in the West Midlands of England. It is the most populous British city outside the capital London, with a population of 1,036,900 , and lies at the heart of the West Midlands conurbation, the second most populous urban area in the United Kingdom with a...
in 1946. There were actually two versions of the A7, the original 495cc version and an improved 497cc version launched in 1950. Although its name was changed to the Star Twin and later the Shooting Star the BSA A7 continued in production with minor modifications until 1961.
Development
Designed by Val PageVal Page
Valentine Page was a British motorcycle designer born in 1892. Described as Britain's greatest motorcycle designer, he worked for most of the leading marques, including Ariel, Triumph, and BSA. He died in 1978.-J.A Prestwich:...
, Herbert Parker and David Munro, the BSA A7 was the first of the BSA twin-cylinder
Cylinder (engine)
A cylinder is the central working part of a reciprocating engine or pump, the space in which a piston travels. Multiple cylinders are commonly arranged side by side in a bank, or engine block, which is typically cast from aluminum or cast iron before receiving precision machine work...
motorcycles and was ready for launch in 1939, but the outbreak of World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
delayed the launch until September 1946 when hostilities ended. The very first A7 off the production line was flown to Paris
Paris
Paris is the capital and largest city in France, situated on the river Seine, in northern France, at the heart of the Île-de-France region...
for the first motorcycle show after the end of the war. There was huge demand for affordable transport after the war and the simplicity of the A7 twin was helped along by the slogan 'It's time YOU had a BSA!'.
Engine
The 495cc twin cylinder engine produced 26bhp and was capable of 85mph. A single camshaftCamshaft
A camshaft is a shaft to which a cam is fastened or of which a cam forms an integral part.-History:An early cam was built into Hellenistic water-driven automata from the 3rd century BC. The camshaft was later described in Iraq by Al-Jazari in 1206. He employed it as part of his automata,...
behind the cylinders operated the valve
Valve
A valve is a device that regulates, directs or controls the flow of a fluid by opening, closing, or partially obstructing various passageways. Valves are technically pipe fittings, but are usually discussed as a separate category...
s via long pushrods passing through a tunnel in the cast iron block. This system needed a considerable number of studs and nuts to fasten down the cylinder head
Cylinder head
In an internal combustion engine, the cylinder head sits above the cylinders on top of the cylinder block. It closes in the top of the cylinder, forming the combustion chamber. This joint is sealed by a head gasket...
and rockerboxes, many of them deeply recessed and requiring well-made box spanners or the (then uncommon) sockets. As with other British motorcycles of the period, this kind of set-up regularly led to oil leaks.
Most motorcycles of this period tensioned the primary chain by drawing or rotating the gearbox backwards on a hinge with threaded rods, this was known as pre-unit construction
Pre-unit construction
Pre-unit construction, also called separate construction, is a motorcycle engine architecture where the engine and gearbox are separate casings, with their own oil reservoirs, and usually attached to parallel plates that also attach to the frame...
. The first A7 featured a fixed gearbox, bolted to the back of the crankcase
Crankcase
In an internal combustion engine of the reciprocating type, the crankcase is the housing for the crankshaft. The enclosure forms the largest cavity in the engine and is located below the cylinder, which in a multicylinder engine are usually integrated into one or several cylinder blocks...
, and an internal tensioner for the duplex primary chain
Chain
A chain is a sequence of connected links.Chain may also refer to:Chain may refer to:* Necklace - a jewelry which is worn around the neck* Mail , a type of armor made of interlocking chain links...
. This gave it the appearance of unit construction and pioneered the system later used in unit-construction engines (e.g. BSA C12/C15, BSA B40, Triumph 3TA and on). However, in 1954 a re-design reverted to the older system. The electrics (as was universal for larger British motorcycles of the period) consisted of two independent systems, the very reliable and self-contained Lucas
Lucas Industries plc
Lucas Industries plc was a famous British manufacturer of components for the motor industry and aerospace industry. It was based in Birmingham. It was listed on the London Stock Exchange and was once a constituent of the FTSE 100 Index...
magneto
Magneto (electrical)
A magneto is an electrical generator that uses permanent magnets to produce alternating current.Magnetos adapted to produce pulses of high voltage are used in the ignition systems of some gasoline-powered internal combustion engines to provide power to the spark plugs...
, with a dynamo generator
Electrical generator
In electricity generation, an electric generator is a device that converts mechanical energy to electrical energy. A generator forces electric charge to flow through an external electrical circuit. It is analogous to a water pump, which causes water to flow...
to charge the battery and provide lights. Carburation
Carburetor
A carburetor , carburettor, or carburetter is a device that blends air and fuel for an internal combustion engine. It is sometimes shortened to carb in North America and the United Kingdom....
was a single Amal remote float Type 6 until 1955 when it was upgraded to a 376 Monobloc.
BSA A7 'Star Twin'
In October 1949 BSA also launched the Bert HopwoodBert Hopwood
Herbert "Bert" Hopwood was a British motorcycle designer. He helped with some of the most influential designs for the British motorcycle industry and worked for Ariel, Norton, BSA and Triumph.-Motorcycle design career:...
designed 650cc twin cylinder BSA A10
BSA Golden Flash
The BSA Golden Flash was a Birmingham Small Arms Company motorcycle. The Golden Flash was also available in black and chrome, but it was the all-over gold paint scheme that gave it the name, and made it such a popular escape from post war austerity....
. Although resembling the A7 500cc twin, it had a revised engine design and a new A7 soon followed, based on the A10 - in response to competition from the Triumph Tiger 100
Triumph Tiger 100
The Triumph Tiger 100 was a British motorcycle first made by Triumph at their Coventry factory for 1939.With the runaway sales success of the Triumph Speed Twin, Edward Turner's mind turned to further developing the potential of his new parallel twin motor...
. Launched as the BSA Star Twin the new model featured twin carburettors and increased compression ratio
Compression ratio
The 'compression ratio' of an internal-combustion engine or external combustion engine is a value that represents the ratio of the volume of its combustion chamber from its largest capacity to its smallest capacity...
. It also had the latest design of cylinder head with austenitic steel inlet and exhaust valves. The uprated engine was fitted to a plunger frame and finished extra chrome. Both models were produced with an option of rigid or plunger frames until 1954 and the introduction of a pivoted fork frame. The new frame also led to a separate gearbox to replace the bolted on version.
BSA A7 'Shooting Star'
In 1954 the Star Twin was redesignated the Shooting Star with a new swinging arm frame and the engine further developed by reducing the stroke to 72.6mm and increasing the bore to 66mm, giving a slight increase in capacity to 497cc. By the end of production in 1961 the BSA Shooting Star was the culmination of the development of the BSA A7, with a deep bottle green colour scheme with light green tank, mudguards and side panels, it had an alloy cylinder head, a duplex cradle frame with swinging arm rear suspension, full-width light alloy hubs and 8-inch drum brakes. Engine compression was upgraded from 6.6:1 to 7:1 and power was up to 30 bhp at 5800rpm, with a top speed of just under 90 mph.Maudes Trophy
In 1952 three BSA A7's were entered for the Maudes TrophyMaudes Trophy
The Maudes Trophy is a motorcycle endurance award established in 1923 by George Pettyt, owner of the manager of the Exeter branch of Maudes Motor Mart to promote an impartially observed test for motorcycles. Pettyt donated a silver trophy for the Auto-Cycle Union to award annually.-Winners:...
and the International Six Days Trial
International Six Days Enduro
The International Six Days Enduro is the oldest 'off road' motorcycle event on the FIM Calendar.The ISDE was first held in 1913 at Carlisle, England. It has occurred annually, apart from interruptions due to World War I and World War II, at various locations throughout the world. The early...
, achieving 4,500 miles without problems and confirming the reliability of the design. All three bikes were randomly selected from the production line, picked up Gold medals and earned BSA the Team award as well as the Trophy. The three bikes were ridden by Brian Martin, Fred Rist and Norman Vanhouse. From Birmingham the team rode to Vienna
Vienna
Vienna is the capital and largest city of the Republic of Austria and one of the nine states of Austria. Vienna is Austria's primary city, with a population of about 1.723 million , and is by far the largest city in Austria, as well as its cultural, economic, and political centre...
then on through Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
, Denmark
Denmark
Denmark is a Scandinavian country in Northern Europe. The countries of Denmark and Greenland, as well as the Faroe Islands, constitute the Kingdom of Denmark . It is the southernmost of the Nordic countries, southwest of Sweden and south of Norway, and bordered to the south by Germany. Denmark...
, Sweden
Sweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....
and Norway
Norway
Norway , officially the Kingdom of Norway, is a Nordic unitary constitutional monarchy whose territory comprises the western portion of the Scandinavian Peninsula, Jan Mayen, and the Arctic archipelago of Svalbard and Bouvet Island. Norway has a total area of and a population of about 4.9 million...
before returning safely and with a clean sheet to Birmingham
Birmingham
Birmingham is a city and metropolitan borough in the West Midlands of England. It is the most populous British city outside the capital London, with a population of 1,036,900 , and lies at the heart of the West Midlands conurbation, the second most populous urban area in the United Kingdom with a...
.
American speed record
Also in 1952 American BSA dealer Hap Alzina prepared a BSA Star Twin for an attempt on the American Class C speed record for standard catalogue motorcycles. The rules prevented major modification but Alzina was allowed to use 80 octaneOctane
Octane is a hydrocarbon and an alkane with the chemical formula C8H18, and the condensed structural formula CH36CH3. Octane has many structural isomers that differ by the amount and location of branching in the carbon chain...
fuel, which together with a compression ratio of 8 to 1 enabled rider Gene Thiessen to achieve a two way record speed of 123.69 mph.