The BSA Bantam is a two-stroke unit construction motorcycle that was produced by BSA from 1948 to 1971. Over 250,000 were sold - some estimates place the number closer to half a million.
BSA Bantam History
The original design of the Bantam came from a German design, the DKW RT125 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 125cc to 175cc.
BSA Bantam 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 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"
BSA Bantam Models
BSA Bantam D1 plunger frame suspension detail. The telescoping "cans" cover and protect the springs. The amount of inner can (chrome) showing and the position of the chainguard indicate the maximum travel that could be expected. The solid rod actuator for the rear brake can also be seen.
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.
Significant Changes throughout Models
The BSA D3 Major represented the next step in development of the Bantam, although the D1 would be produced for many years to come. With the increased power from the larger engine a twin seat was fitted; this had been an option on the D1 which otherwise had a parcel carrier behind the sprung "saddle" seat.
The BSA Bantam D175 - Also known as B175. Was a minor reworking of the D14/4. The spark plug sits in line with the cylinder head, front forks are stronger, slightly lower compression ratio at 9.5, separate headlight with high-beam warning, exposed rear shock springs, strengthened kickstart shaft, revised fixing on crankshaft compression disc plates.
An off-road model called the Bushman was also available. Only three hundred remained in the UK the rest were exported to Australia.
All UK BSA Bushman models carry the engine number prefix BB.