The BSA B40 was a series of unit construction single-cylinder OHV four-stroke motorcycles made by the Birmingham Small Arms Company. Developed from the BSA C15, the machines were produced between 1961 and 1967 for civilian use. Military versions were manufactured from 1967 to 1970. Around 14,000 machines were built in total.
Overview
As a reaction to the emergence of high-tech, high performance Honda lightweights that were starting to appear (Mike Hailwood had won the 1961 Lightweight TT on a DOHC, twin-cylinder, 125 cc machine), BSA increased the performance its lightweight by boring the C15 out to 350 cc.
The 67 mm bore of the C15 was increased to 79 mm to give a capacity of 343 cc for the new B40 model. Although the bottom end was beefed up, it still retained the plain big end. Concerns over reliability led to the compression ratio to be reduced to 7:1. A new cast iron barrel was produced with the pushrod tunnel built in. The engine produced at 7,000 rpm.
C15 cycle parts were retained except for heavier duty front forks, a 7" front brake and 18" wheels.
Sports, enduro/trials, military and police versions were produced during the model's lifetime.
Models
B40 Star
The first model of the series was the B40 Star, introduced in 1961. The new 350 cc engine had 21 bhp, which gave a cruising speed of 50 - 55 mph and a top speed of 75 mph. The Star had deeply valenced, painted mudguards; metal fork shrouds and the headlamp was fitted in a nacelle. Finish was red with black frame and forks or all black. American variants had chrome sides to the petrol tank.
In 1962, the big end was changed from plain bearings to roller bearing, and in 1965 the points were moved from the 'distributor'-type device behind the cylinder to the timing case, and the clutch operating mechanism redesigned.
Very few machines were made in 1967, its final year. These machines were fitted with a roller bearing timing side main bearing. These engines, prefixed BD40G, are generally acknowledged as having the most robust bottom end.
The model was initially known as the Star Sportsman in the US, but this was changed to the Star in 1962 ahead of the SS90 model being launched. In 1964 the name was changed again in the US to the Super Star.
B40 Sports Star SS90
Launched in June 1962, the B40 Sports Star SS90 had similar tuning modifications to the C15 SS80. The compression ratio was raised to 8.75:1, larger valves and a bigger carburettor, which raised the power to @ 7,000 rpm. The machine was fitted with a roller bearing big end and a close ratio gearbox. Initially UK SS90 models were distinguished by the chrome sides of the petrol tank.
Introduced in the US in 1963 as the BSA SS90, the American model was finished in blue and had chrome mudguards and rubber gaiters instead of metal fork shrouds. In 1964, the US model was referred to as the Sportsman, and the UK model was fitted with the chrome mudguards. In 1965 both variants were fitted with a separate headlight, the US version now being called the Super Sports.
B40 Enduro Star
First introduced in 1963 in limited quantities the US-only B40 Enduro Star went into full production in 1964. The model was built around a trials frame a 19" front wheel to give good ground clearance. It had an alloy tank, single seat, high-level exhaust and a half width 7" front brake. The machine had the low compression engine and a wide ratio gearbox. Although the machine was street legal and fitted with lights, no battery was fitted.
The model won numerous competitions in America, including the 1963 500 mile Jack Pine Lightweight Competition and the 1964 National Championship Endurance Run. The model was discontinued after 1965.
B40 Police
A special police version, the B40 Police, was produced in 1964 and 1965.
Military versions
B40 WD
In 1965, the newly formed Royal Corps of Transport, who took over the responsibility from army transportation, issued a requirement for a motorcycle to replace its ageing fleet of mainly BSA M20 and Matchless G3/L machines. BSA submitted four B40s built to army specifications for evaluation by the Fighting Vehicles Research and Development Establishment near Chertsey, Surrey. Triumph also submitted four 500 cc machines. Both types had major defects and modified versions were submitted for further evaluation. After an 10,00 mile reliability test, an order was placed for 2,000 B40s, 880 of these being destined for the BAOR. The initial order was delivered in 1967 and further machines supplied until 1970.