BSA A7 Star Twin/Shooting Star

 

 

 

Make Model

Up to 1954: A7 Star Twin

After 1954:  A7 Shooting star

Year

1946 - 61

Engine

Straight twin cylinder, 4-stroke

Capacity

Up to 1950: 495 cc / 30.2 in.

After 1950:  497 cc / 30.3 in/

Bore x Stroke

66 x 72.6mm

Cooling System Air cooled

Compression Ratio

Star Twin: 6.6:1

Shooring Star: 7.2:1

Oil Capacity 2.6 L / 5.5 US pints

Carburetor

Up to 1954: Amal remote float type 6

After 1954:  Amal 376 monobloc

Exhaust Twin, chrome

Generator

Dynamo

Ignition 

Lucas magneto

Spark plug

Star Twin: L10S

Shooring Star: NA 10

Battery 12 V
Starting Kick

Max Power

495 cc:  19 kW / 26 hp @ 5800 rpm

497 cc:  22 kW / 30 hp @ 5800 rpm

Clutch Multi-plate, dry

Transmission 

4-Speed
Final Drive Chain, 98 links
Gear Ratios 1st 13.62 / 2nd 9.28 / 3rd 6.38 / 4th 5.28:1
Frame Twin cradle
Wheelbase 1391 mm / 54.8 in

Front Suspension

Star Twin: Girder

Shooting Star:  Telefork

Rear Suspension

Shooting Star: Swinging arm

Front Brakes

Shooting Star: 8 in

Rear Brakes

Shooting Star: 8 in
Wheels Steel, wire spokes

Front Tyre

3.25 x 19 in

Rear Tyre

3.50 x 19 in

Dry Weight

166 kg / 366 lbs

Fuel Capacity 

16 L / 4.2 US gal or 8 L / 2.1 US gal

Top speed

495 cc: 137 km/h / 85 mph

497 cc:  40 km/h / 90 mph

Colours Bottle green/Light green
Source Wikipedia

"Star Twin Badge"

There were two versions of the A7, the original 495 cc (30.2 cu in) version, and an improved 497 cc (30.3 cu in) 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.

Designed by Val Page, 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!'.

The 495 cc (30.2 cu in) twin cylinder engine produced 26 bhp (19 kW) and was capable of 85 mph (137 km/h).[1] A single camshaft behind the cylinders operated the valves 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 had 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 such as the BSA C12/C15, BSA B40, Triumph 3TA and so 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.

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 72.6 mm and increasing the bore to 66 mm, giving a slight increase in capacity to 497 cc. 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 (22 kW) at 5800 rpm, with a top speed of just under 90 mph (140 km/h).