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.
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"
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 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"
The 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
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 Bushman models carry the engine number