The BSA A7 was a 500cc
motorcycle
A motorcycle (motorbike, bike; uni (if one-wheeled); trike (if three-wheeled); quad (if four-wheeled)) is a lightweight private 1-to-2 passenger personal motor vehicle Steering, steered by a Motorcycle handlebar, handlebar from a saddle-style ...
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 its factory in Armoury Road,
Small Heath
Small Heath is an inner-city area in south-east Birmingham, West Midlands (county), West Midlands, England situated on and around the Coventry Road about from the city centre.
History
Small Heath, which has been settled and used since Roman t ...
,
Birmingham
Birmingham ( ) is a City status in the United Kingdom, city and metropolitan borough in the metropolitan county of West Midlands (county), West Midlands, within the wider West Midlands (region), West Midlands region, in England. It is the Lis ...
. 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 The various A7 models continued in production with minor modifications until 1961/2 when they were superseded by the unit-construction A50 model.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 Engineering, Triumph at their Coventry, and later Meriden factories. Edward Turner (motorcycle designer), Edward Turner, Triumph's Chief Designer and managing director, launch ...
, BSA needed a 500cc twin to compete with it. Designed by Herbert Parker, David Munro and BSA's chief designer,
Val Page
Valentine Page (1891–1978) was a British motorcycle designer. He worked for leading UK marques including JAP, Ariel, Triumph, and BSA. Page was an innovator whose radical designs include the Triumph 6/1; BSA Gold Star, M20, and A7; Ari ...
, the BSA A7 was the first of the BSA twin-
cylinder
A cylinder () 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 infinite ...
motorcycles. The outbreak of
World War II
World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...
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 city, capital and List of communes in France with over 20,000 inhabitants, largest city of France. With an estimated population of 2,048,472 residents in January 2025 in an area of more than , Paris is the List of ci ...
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 syst ...
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 Slurry, slurries) by opening, closing, or partially obstructing various passageways. Valves are technically Pip ...
s via long
pushrod
A valvetrain 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) into the combu ...
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 a piston engine, the cylinder head sits above the cylinders, forming the roof of the combustion chamber. In sidevalve engines the head is a simple plate of metal containing the spark plugs and possibly heat dissipation fins. In more modern ...
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 designed motorcycles for Ariel, Norton, BSA and Triumph.
Motorcycle design career
Hopwood left school at an early age to work for Ariel under designer Val Pa ...
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
A transmission (also called a gearbox) is a mechanical device invented by Louis Renault (who founded Renault) which uses a gear set—two or more gears working together—to change the speed, direction of rotation, or torque multiplication/r ...
backwards on a hinge with threaded rods, this was known as
pre-unit construction. The first A7 had a fixed gearbox, bolted to the back of the
crankcase
A crankcase is the housing in a reciprocating engine, piston engine 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, res ...
, 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 ...
. 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
Lucas
Lucas or LUCAS may refer to:
People
* Lucas (surname)
* Lucas (given name)
Arts and entertainment
* Luca Family Singers, or the Lucas, a 19th-century African-American singing group
* Lucas, a 1960s Swedish pop group formed by Janne Lucas Perss ...
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 to charge the battery and provide lights.
Carburation was initially a single
Amal remote float Type 6. Later
Amal TT and then
376 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. Seve ...
, BSA launched the A7SS Star Twin. The new model had increased
compression ratio
The compression ratio is the ratio between the maximum and minimum volume during the compression stage of the power cycle in a piston or Wankel engine.
A fundamental specification for such engines, it can be measured in two different ways. Th ...
. 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 K ...
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 Monobloc 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 ...
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
Vienna
Vienna ( ; ; ) is the capital city, capital, List of largest cities in Austria, most populous city, and one of Federal states of Austria, nine federal states of Austria. It is Austria's primate city, with just over two million inhabitants. ...
then on through Germany, Denmark, Sweden and Norway before returning safely and with a clean sheet to
Birmingham
Birmingham ( ) is a City status in the United Kingdom, city and metropolitan borough in the metropolitan county of West Midlands (county), West Midlands, within the wider West Midlands (region), West Midlands region, in England. It is the Lis ...
.
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 also an alkane with the chemical formula C8H18, and the condensed structural formula CH3(CH2)6CH3. Octane has many structural isomers that differ by the location of branching in the carbon chain. One of these isomers ...
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, Daytona Beach, Florida. The race was founded in 1937 when it was sanctioned by the American Mo ...
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 Birmingham Small Arms Company, BSA from 1938 to 1963. They were 350 cc and 500 cc Single-cylinder engine, single-cylinder Four-stroke engine, four-stroke production motorcycles known for bein ...
finished in 3rd.
Related Models
In 1960 the
Akashi-based
Kawasaki Aircraft Company acquired an interest in the
Meguro
is a Special wards of Tokyo, special ward in the Tokyo, Tokyo Metropolis in 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 ...
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 per cent by the new
Kawasaki Motorcycle Corporation
is a Japanese mobility manufacturer that produces motorcycles, all-terrain vehicles, utility vehicles, watercraft, outboard motors, and other electric products. It derives its origins from Kawasaki Aircraft Industries, a subsidiary of Kawasa ...
, 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 , called (TMS) until 2023, 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 recog ...
. 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.
See also
*
List of motorcycles of the 1940s
This a listing of motorcycles of the 1940s, including those on Sales, sale, introduced, or otherwise relevant in this period.
Motorcycle
*Acme motorcycle (1939–49)
*AJS 18
*AJS 7R
*AJS Model 16
*AJS Model 20
*AJS Porcupine
*Ariel Red Hunter
...
References
External links
BSA A7 review
{{BSA motorcycles, state=collapsed
A7
Motorcycles introduced in the 1940s
Motorcycles powered by straight-twin engines