Major Portals
Home
Motorcycle designers
Motorcycle engineers
Motorcycle manufacturers
Motorcycle pioneers
Motorcycle racing
My motorcycles
Sources
Page Menu
What links here
Site Menu
Recent updates
BSA Bantam
BSA Bantam
UK
BSA Bantam
Manufacturer BSA
Production 1948 - 1971
Engine 2-stroke 125 cc (D1)
150 cc (D3)
175 cc (D5 Onwards)
Power 4.5 bhp (3.4 kW) (D1)
5.3 bhp (4.0 kW) (D3)
7.4 bhp (5.5 kW) (D5 & D7)
10 bhp (7.5 kW) (D10)
12.6 bhp (9.4 kW) (D14/4 & B175)
Transmission Three speed gearbox (D1-D10) Four speed gearbox (D14/4-B175)
Fuel Capacity 1.75 imp gal (8.0 l; 2.10 US gal) ("Teardrop" Tanks)
2 imp gal (9.1 l; 2.4 US gal) (D5 & D7)
1.9 imp gal (8.6 l; 2.3 US gal) (D7 Deluxe onwards)

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 in fact a German design, the DKW RT 125, received as war reparations. 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 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 famous DKW RT 125 of 1950
The famous DKW RT 125 of 1950

The BSA designers converted the design to Imperial measurements for manufacture in Birmingham. This original Bantam, the D1, was released in October 1948 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 recognisable 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

125 cc engine on a Bantam D1
125 cc engine on a Bantam D1

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.

Bantam D1 plunger frame suspension detail
Bantam D1 plunger frame suspension detail

Pre-1958 (D1 to D5) had 19 inch wheels and 4.5 inch brakes. The 1959 D7 and later models had 18 inch wheels and 5 inch brakes front and rear. Describing the rear suspension as "Swinging Arm" is universal amongst English speakers, but every machine so described (and from every manufacturer, until the 1980s) would be better called swinging fork.

Developments and models

Bantam D7
Bantam D7

D3 Major

The D3 Major represented the first step in development of the Bantam, although the D1 would be produced for many years to come. First produced in late (most likely October was the first released) 1953 the D3 continued in production until 1957. A modern-style foam-filled pillion seat was fitted as standard, an economy and comfort breakthrough that had become popular as an option on the D1. It replaced the original standard fitting of a parcel carrier behind an individual sprung rubber seat.

Bushman, nore high exhaust
Bushman, note high exhaust

In addition, the front suspension was made more substantial in volume and the cylinder was not simply bored out but was enlarged with distinctive larger thermal cooling fins. These larger cooling fins was also added to the post-1953 D1 models, albeit they maintained their smaller bore.

D175/B175

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 (as they are from the larger capacity BSA C15), 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.

Bushman

The off-road Bushman version was available as an export model, for Australia in particular, but 300 were sold in the UK.
All UK Bushman models carry the engine number prefix BB.

BSA Bantam gallery


Categories: BSA motorcycles