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
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"
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
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.