The BSA Bantam is a two-stroke unit construction motorcycle that was produced by the Birmingham Small Arms Company (BSA) from 1948 (as a 125 cc) until 1971 (as a 175 cc). Exact production figures are unknown, but it was over 250,000 and some estimates place the number closer to half a million.
History
Despite the Bantam being considered the archetypal 'truly British' lightweight motorcycle outselling all others, it was based on a German design. The Bantam was based on the DKW RT 125, a design that was received as war reparations, with the Bantam as a mirror image so the gearchange was on the right side as with other British motorcycles of the period. The same design went into production in at least two, and perhaps four, other countries. Harley-Davidson started producing their Model 125 in late 1947 (several months before BSA) and the occupiers of East Germany, the U.S.S.R. began building the Москва (Moskva) M1A model even earlier, c.1946. In East Germany the machine was made at the original DKW factory by IFA, which later became MZ and Japan also produced copies.
The BSA designers made the design a mirror image with right hand side controls and Imperial fittings for manufacture in Birmingham. This original Bantam, the D1, was released in 1948 outside of the UK and was released in the UK in 1949, and continued in production for several years. It had telescopic forks, a rigid rear end, direct electrics, shovel front-mudguard and fishtail silencer, was available only in "mist green" and sold for £60 plus tax. Although the frame changed out of recognition (beginning with conversion to plunger and then swinging fork rear suspension), the engine remained a recognizable development of the original for the entire 23 years of production.
Engine
The engine is a unit construction (engine and gearbox of one piece) single cylinder 2 stroke. The barrel is cast iron while the head is alloy. The gearbox was initially three speeds, later versions went to four, fed through a "wet" clutch. Ignition was of two types: a Lucas battery-powered coil in earlier machines, or a magneto by Wipac. The magneto was on a composite assembly sitting within the flywheel with its magnet inserts; windings gave power either directly to the lights (with a dry cell for when the engine was stopped) or through a rectifier into a lead acid battery. The early D1s had "fish tail" styled exhausts but this was replaced with the more conventional cylindrical silencer. High-level exhausts were made for the trials and off-road models, in which the only electrics are the magneto-powered ignition.
Models
This listing shows only the main variants and most models were available with refinements or in competition form. BSA had used a lettering system for their range of motorcycles and started the "D" series for their first two-stroke. The D175 was marketed as the B175 as BSA struggled against imports in the late 60s to its closure in 1972 (the larger capacity "B" series having helped make them the largest motorcycle manufacturer in the world). The engine size shown is nominal, British motorcycles were made 1 or 3 cc smaller than their tax bracket maximum to allow for re-bores and wear.
Pre-1958 (D1 to D3) had 19 inch wheels and 4.5 inch brakes. The 1958 D5 had 18 inch wheels and 4.5 inch brakes. 1959 D7 and later models had 18 inch wheels and 5 inch brakes front and rear.
Developments and models
D1
The D1 (the original model) 125cc was available initially only with a rigid rear suspension, although within three years the range was enhanced to include an optional plunger rear suspension. The front suspension of all D1's possessed no damping and resulted in a bouncy ride quality. D1's were available with a variety of electrical lighting systems. Wipac systems were available either in 6v AC (known as direct lighting) or DC. The AC system used a small dry 'torch' cell battery to illuminate the forward facing 'pilot' bulb within the headlamp shell, the remaining lighting was only available for use when the engine was running and the dry cell had to be regularly replaced. The DC system incorporated a lead acid battery and operated in a conventional manner. For a short period some D1's were equipped with Lucas lighting systems and these operated in a similar manner to the Wipac DC system. The D1 continued to be available to the public right up until 1963 and was still produced for the GPO (General Post Office) for at least 2 more years.