The original design of the Bantam came from a German design, the DKW RT 125 (de) that was received as part of war reparations. This fact was not made widely known until long after the demise of BSA and for many years the Bantam was thought by many to be a ‘truly British’ lightweight motorcycle despite the original DKW design being taken up by two other manufacturers – Harley Davidson for one.
The BSA designers converted the design to meet British conventions – creating a mirror image – and into Imperial measurements for manufacture in Birmingham. This original Bantam, the D1, would continue to be produced for several years. Subsequent members of the Bantam range differed markedly in frame but their engine was a development of the original.
The first Bantams were available only in all-over “mist green”, and sold for £60 plus tax. Later models changed distinctly from the original; over the years it gained improved suspension including a rear swinging arm, electrics and the engine size increased from 125 to 175 cc.
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 a flattened fish tail style exhaust. This was replaced with a more conventional round tube exhaust which ran at a higher level on trials and off-road models such as the “Bushman”
Developed from the pre-war DKW RT125 and announced in 1948, the Bantam became a top seller for BSA, in excess of half a million leaving the Birmingham factory before production ceased in 1971. Originally of 123cc, the engine grew first to 148cc and then to 172cc. Plunger rear suspension became available as an option in 1950, as did battery electrics powered by a 6-volt Lucas alternator, direct lighting having been relied upon hitherto.
The introduction of the 172cc D10 model in 1966 marked a number of important technical developments for the ever-popular Bantam, the most important of which were a change to coil ignition, replacing the old flywheel generator, and the adoption of a 4-speed gearbox, while a raised compression ratio and bigger carburettor increased maximum power to 10bhp and the top speed to 62mph. Introduced for 1968, the successor D14 Bantam boasted a more powerful engine producing 12.6bhp. All three models – Supreme, Sports and Bushman – used the four-speed gearbox first seen on the preceding D10 while the latter pair boasted new, heavy-duty front forks.
D7 Bantam Super
Many a now-mature motorcyclist’s first 2-wheeled experience will have been gained aboard a BSA Bantam, a model that was produced in various forms for over 20 years. The introduction of the first 172cc model – the D5 – for 1958 marked a number of developments, the most important of which were a stronger big-end bearing and improved lubrication. A raised compression ratio and larger carburettor increased maximum power to 7.4bhp and the top speed to 59mph. Introduced for 1959, successor D7 model – known as the Bantam Super – featured the 172cc engine while boasting a new frame, hydraulically damped front fork, bigger brakes and up-swept handlebars.
Main variants listed, most models were also available in competition form or with extra refinements. Nominal engine sizes given. BSA used a lettering system for their range of motorcycles. BSA decided to use a different letting system for the Bantam as it was a two-stroke, but with the introduction of the B175/D175 the company saw it more appropriate to label it with the “B” lettering system as by that time the engine size had increased to the capacity of those in the “B” category.