The BSA A7 was a 500cc

motorcycle A motorcycle (motorbike, bike, or trike (if three-wheeled)) is a two or three-wheeled motor vehicle steered by a handlebar. Motorcycle design varies greatly to suit a range of different purposes: long-distance travel, commuting, cruising ...

model range made by

Birmingham Small Arms Company The Birmingham Small Arms Company Limited (BSA) was a major British industrial combine, a group of businesses manufacturing military and sporting firearms; bicycles; motorcycles; cars; buses and bodies; steel; iron castings; hand tool, hand, po ...

(BSA) at their factory in Armoury Road,

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Birmingham Birmingham ( ) is a city and metropolitan borough in the metropolitan county of West Midlands in England. It is the second-largest city in the United Kingdom with a population of 1.145 million in the city proper, 2.92 million in the West ...

. The range was launched in 1946 using a long stroke engine. An improved version based on the BSA A10 engine was launched in 1950. The various A7 models continued in production with minor modifications until 1961/2 when they were superseded by the unit-construction A50 model.

Development

After the 1938 launch of the Edward Turner designed

Triumph Speed Twin The Speed Twin 5T is a standard motorcycle that was made by Triumph at their Coventry, and later Meriden factories. Edward Turner, Triumph’s Chief Designer and Managing Director, launched the Triumph Speed Twin at the 1937 National Motorcyc ...

, BSA needed a 500cc twin to compete with the Speed Twin. Designed by Herbert Parker, David Munro and BSA's chief designer,

Val Page Valentine Page (1891–1978)cylinder A cylinder (from ) has traditionally been a three-dimensional solid, one of the most basic of curvilinear geometric shapes. In elementary geometry, it is considered a prism with a circle as its base. A cylinder may also be defined as an infin ...

motorcycles. The outbreak of

World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...

delayed the launch and several prototypes were built during the war years. The model was finally launched in September 1946 when hostilities had ended. The very first A7 off the production line was flown to

Paris Paris () is the capital and most populous city of France, with an estimated population of 2,165,423 residents in 2019 in an area of more than 105 km² (41 sq mi), making it the 30th most densely populated city in the world in 2020. S ...

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 twin cylinder engine produced and was capable of . The engine had a long stroke with a bore and stroke of . A single

camshaft A camshaft is a shaft that contains a row of pointed cams, in order to convert rotational motion to reciprocating motion. Camshafts are used in piston engines (to operate the intake and exhaust valves), mechanically controlled ignition systems ...

behind the cylinders operated the

valve A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically fittings ...

s via long

pushrod A valvetrain or valve train is a mechanical system that controls the operation of the intake and exhaust valves in an internal combustion engine. The intake valves control the flow of air/fuel mixture (or air alone for direct-injected engines) ...

s passing through a tunnel in the cast iron

block Block or blocked may refer to: Arts, entertainment and media Broadcasting * Block programming, the result of a programming strategy in broadcasting * W242BX, a radio station licensed to Greenville, South Carolina, United States known as ''96.3 ...

. This system needed a considerable number of studs and nuts to fasten down the cast iron

cylinder head In an internal combustion engine, the cylinder head (often abbreviated to simply "head") sits above the cylinders and forms the roof of the combustion chamber. In sidevalve engines, the head is a simple sheet of metal; whereas in more modern ov ...

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. In October 1949 BSA launched the

Bert Hopwood Herbert Hopwood (1908 – 17 October 1996) was a British motorcycle designer. He was, at least, partly responsible for some of the most influential designs for the British motorcycle industry and worked for Ariel, Norton, BSA and Triumph. ...

designed 650 cc twin cylinder A10. The engine in the A10 was a redesigned and improved version of the A7 engine. A 497 version of the redesigned engine was produced for the A7. Initially fitted in the new A7S Star Twin, it was also fitted to the base A7 model in 1951. The new engine had a shorter stroke with bore and stroke dimensions of . Most motorcycles of this period tensioned the primary chain by drawing or rotating the

gearbox Propulsion transmission is the mode of transmitting and controlling propulsion power of a machine. The term ''transmission'' properly refers to the whole drivetrain, including clutch, gearbox, prop shaft (for rear-wheel drive vehicles), differe ...

backwards on a hinge with threaded rods, this was known as

pre-unit construction Pre-unit construction, also called separate construction, is a motorcycle engine architecture where the engine and gearbox are separate components with their own oil reservoirs, linked by a driving chain within a primary chaincase. Mounting plate ...

. The first A7 had a fixed gearbox, bolted to the back of the

crankcase In a piston engine, the crankcase is the housing that surrounds the crankshaft. In most modern engines, the crankcase is integrated into the engine block. Two-stroke engines typically use a crankcase-compression design, resulting in the fuel/a ...

, and an internal tensioner for the duplex primary

chain A chain is a serial assembly of connected pieces, called links, typically made of metal, with an overall character similar to that of a rope in that it is flexible and curved in compression but linear, rigid, and load-bearing in tension. A c ...

. However, in 1954 when the swinging arm was introduced, the re-design reverted to the older system of a separate gearbox. The electrics (as was universal for larger British motorcycles of the period) consisted of two independent systems, the very reliable and self-contained

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magneto A magneto is an electrical generator that uses permanent magnets to produce periodic pulses of alternating current. Unlike a dynamo, a magneto does not contain a commutator to produce direct current. It is categorized as a form of alternator, ...

, with a dynamo

generator Generator may refer to: * Signal generator, electronic devices that generate repeating or non-repeating electronic signals * Electric generator, a device that converts mechanical energy to electrical energy. * Generator (circuit theory), an eleme ...

to charge the battery and provide lights. Carburation was initially a single

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remote float Type 6. Later

Amal TT AMAL was a British engineering company servicing the motorcycle and other light-engineering motor industries between 1927 and 1993376 Monobloc carbs were used.

Cycle Parts

The A7 was launched with a rigid frame and telescopic front forks. One useful feature was a hinged rear mudguard that lifted up to allow the rear wheel to be removed more easily. Plunger rear suspension was offered as an option to the rigid frame from 1949. Concerned about the high wear rate of the plunger suspension that lead to poor handling a swinging arm frame was introduced in 1954 and the rigid and plunger frames discontinued.

Model Range

Overview of models

All models are swinging arm frame unless otherwise indicated. Notes

A7

The A7 was launched in 1947 with a rigid frame and the "long stroke" engine with iron barrels and cylinder head. Plunger suspension was offered as an alternative from 1949. The engine was changed to the shorter stroke A10 based design in 1951. The rigid frame was discontinued in 1953 and the plunger in 1954. From 1954 the swinging arm frame was produced, and the name "Flash" given to the model in the US market. An alternator was offer as an alternative to the dynamo from 1961. Production ceased in 1962 when the unit construction A50 was introduced.

A7S Star Twin

In response to competition from the

Triumph Tiger 100 The Tiger 100 (T100) was a standard motorcycle first made by the British motorcycle company Triumph in 1939. Production ceased when the Triumph factory was destroyed by German bombing in 1940 during World War 2, but recommenced in 1946. Several ...

BSA launched the A7SS Star Twin. The new model had increased

compression ratio The compression ratio is the ratio between the volume of the cylinder and combustion chamber in an internal combustion engine at their maximum and minimum values. A fundamental specification for such engines, it is measured two ways: the stati ...

. It had the later A10 based engine and the latest design of cylinder head with

austenitic Austenite, also known as gamma-phase iron (γ-Fe), is a metallic, non-magnetic allotrope of iron or a solid solution of iron with an alloying element. In plain-carbon steel, austenite exists above the critical eutectoid temperature of 1000 ...

steel inlet and exhaust valves. The inlet manifold was separate from the cylinder head so twin carburettors could optionally be fitted. The uprated engine was fitted to a plunger frame and finished extra chrome. The model was produced with an option of rigid or plunger frames. In 1953 a new alloy head was fitted together with an Amal Monoblock carburettor. The model was discontinued in 1954 in favour of the "Shooting Star" model.

A7SS Shooting Star

The Shooting Star was introduced in 1954 with a new swinging arm frame. The engine had a hotter cam, and compression was upgraded from 6.6:1 to 7:1. Power was up to at 5800 rpm, with a top speed of just under . The earlier models had a dark green frame and a separate carburetor manifold fitted to the alloy cylinder head. By the end of production in 1962 the BSA Shooting Star was the culmination of the development of the BSA A7, with a black frame 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 cast iron hubs and 8-inch drum brake at the front with a 7-inch at the rear.

Sporting Success

1952 Maudes Trophy

In 1952 three BSA A7s were entered for the

Maudes Trophy The Maudes Trophy is a motorcycle award established in 1923 by George Pettyt, owner of Maudes Motor Mart based in Great Portland Street, London who promoted an impartially-observed endurance test for motorcycles and provided a challenge award to t ...

and the International Six Days Trial, achieving 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

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then on through Germany, Denmark, Sweden and Norway before returning safely and with a clean sheet to

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

octane Octane is a hydrocarbon and an alkane with the chemical formula , and the condensed structural formula . Octane has many structural isomers that differ by the amount and location of branching in the carbon chain. One of these isomers, 2,2,4-Tri ...

fuel, which together with a compression ratio of 8 to 1 enabled rider Gene Thiessen to achieve a two way record speed of .

1954 Daytona 200

In 1954 Bobby Hill won the

Daytona 200 The Daytona 200 is an annual motorcycle road racing competition held in early spring at the Daytona International Speedway in Daytona Beach, Florida. The race was founded in 1937 when it was sanctioned by the American Motorcyclist Association ...

riding a rigid framed Shooting Star. (The rigid frame version was a special order from the factory). The race had one straight asphalt and the other on the beach during the 1950s. Of the 107 starters only 44 finished. Shooting Stars finished 1st, 2nd, 4th and 5th. A

BSA Gold Star The BSA Gold Star is a motorcycle made by BSA from 1938 to 1963. They were 350 cc and 500 cc single-cylinder four-stroke production motorcycles known for being among the fastest bikes of the 1950s. Being hand built and with many opt ...

finished in 3rd.

Related Models

In 1960 the

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-based Kawasaki Aircraft Company acquired an interest in the

Meguro is a special ward in Tokyo, Japan. The English translation of its Japanese self-designation is Meguro City. The ward was founded on March 15, 1947. Meguro is predominantly residential in character, but is also home to light industry, corporate ...

motorcycle company, which had obtained a license to produce a copy of the 500 cc BSA A7. Meguro had been Japan's largest motorcycle manufacturer but in the late 1950s its models had become less competitive and it was short of money. Kawasaki's investment enabled Meguro to launch its A7 copy as the Meguro K. In 1963 Meguro was taken over one hundred percent by the new

Kawasaki Motorcycle Corporation Kawasaki Heavy Industries Motorcycle & Engine Company (川崎重工業モーターサイクル&エンジンカンパニー) is a division of Kawasaki Heavy Industries that produces motorcycles, ATVs, utility vehicles, jet ski personal watercraft, ...

, which maintained the licensing agreement with BSA and continued to build the K model, but due to lubrication problems Kawasaki made engine modifications and the Kawasaki K2 entered production in 1965 with improved crankshaft bearings and a larger oil pump. Since the introduction of the K2, the Meguro K model has tended to become known retrospectively as the K1. In 1965 the K2 was enlarged to 624 cc to become the Meguro X-650 prototype, which was displayed at the 1965

Tokyo Motor Show The is a biennial auto show held in October–November at the Tokyo Big Sight, Tokyo, Japan for cars, motorcycles and commercial vehicles. Hosted by the Japan Automobile Manufacturers Association (JAMA), it is a recognized international show by ...

. The X-650 then became in turn the prototype for the Kawasaki W1. For the new Kawasaki big bike, the traditional look of Meguro motorcycles was replaced with a sleeker fuel tank, sportier mudguards (fenders) and other details intended to appeal to export markets, especially North America.

References

External links

BSA A7 review

{{BSA motorcycles, state=collapsed A7 Motorcycles introduced in the 1940s Motorcycles powered by straight-twin engines