BSA Bantham D3 – The little grey fellow

This relatively rare interim 148cc Bantam, between the 125cc and the 175cc, was still a useful step up from the popular D1.

Words: STEVE WILSON
Photographs: GARY CHAPMAN
Published: The Classic MotorCycle – January 2022

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This particular diminutive BSA, a 1956 D3 Bantam Major 150, is unusual in a couple of ways.

Firstly, the 148cc variant, usually finished overall in Pastel Grey, was only made for four years, from 1954, so there are fewer about than the ubiquitous D1 125s, or the many later 175cc versions.

And secondly, for this Major’s current keeper, Alex Taylor, it’s exceptional, as his friends have gleefully noted, due to its smart finish. Alex, more than capable with the spanners, has a floating collection of classics, several of which have previously featured in these pages. While all have been stripped and refurbished mechanically, Alex tends to leave the cosmetics as found, with the resulting look either “patinated” or “ratty”, your choice.

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The D3, previously restored for sale at Bonhams in the early 2000s, is very much the exception. Its only major deviation from standard is the green-covered dualseat, which suits it as well or better than the stock seat-cover’s two-tone grey.

Amal carb with ‘strangler’ choke/air filter, new tool and battery boxes for new frame, and 1956’s longer, less restrictive silencer.
Amal carb with ‘strangler’ choke/air filter, new tool and battery boxes for new frame, and 1956’s longer, less restrictive silencer.

The usual suspects

Alex is no stranger to Bantams. At the age of 19 he had ridden his original D1 from his Oxfordshire home to Fleet in Hampshire, with his leg in plaster propped up on one of the Bantam’s tin leg-shields. His current D1 (see TCM June 2020) takes him to Cyclemotor and VMCC meetings and runs locally.

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He acquired the D3 from a high-end car and boat dealer in Hampshire, for a sensible ‘trade’ price as it was only an intermittent starter. The problem was a usual one with these little two-strokes – the electrics. On stripping, things were found to be mechanically sound, but the poorly designed centrestand, again as per usual, was chronically unstable. The D-shaped speedo was also u/s, but that was rebuilt (eventually) by a specialist local to the vendor.

The electrics were found to be a mess. This D3 was a Wipac battery version (the Lucas type had been discontinued for 1954), as opposed to a Direct Lighting variant; so its system incorporated a DC rectified circuit for the battery. Alex fitted a new ignition switch and a new coil, noting that the old one was an original. The heart of the six volt system on Bantams, until the 1967 introduction of alternator electrics, was the Wico-Pacy S55 Mark 8 generator, fitted since 1951, in effect a cross between a magneto and an alternator. Alex found this one in good order, but changed the regulator/rectifier for a modern Japanese one, and uprated to 12 volts.

The lighting system, fitted with a diode, once Alex had worked out the low/high beam settings, produced bright lights for evening rides to club meetings, “not like the original dog-end six volt ones”. The rectifier had cost £6, a 12 volt battery £12, and the ignition coil £25.

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For a further £30 the brakes were relined with shoes which, like some other parts, came from Brit Bits in Dorset (Tel: 01202 483675). Alex welded up the centrestand, which is now one of the most stable Bantam ones I have encountered. This had involved another £11.50, for matching paint from Halfords, as like the D1’s Mist Green, the D3’s Pastel Grey finish had been applied to all cycle parts, centrestand included. The mid-1950s was still, just, the immediate post-Second World War era, when flamboyance was disapproved of in the still-austere UK, but the D3’s grey, with its naval overtones, was lightened by the red-lined, cream yellow tank panels and their cheerful Bantam Cockerel emblem – actively crowing in the 150’s case!

D-shaped Smiths speedo habitually ran up to 10mph optimistic, but this one had just been rebuilt.
D-shaped Smiths speedo habitually ran up to 10mph optimistic, but this one had just been rebuilt.

The D3 story

As everyone now knows – though the information was strictly embargoed in postwar Britain – the Bantam’s design was that of the German DKW RT125 (the ‘RT’ stood for ‘Reich’s Type’).Taken as war reparation, at BSA’s Studley Road, Redditch factory, this was simply restyled and mirror-imaged to give a British-style right-foot gear change.

The engines continued to be manufactured at Redditch (mostly by men), after the D1’s 1949-on phenomenal success, at a rate of 300 and soon 400 a week. The complete machines were then assembled at BSA’s Small Heath main works (mostly by women, paid about half the male rate, which helped keep the Bantam’s cost down…), with 90 built a day at their mid-1950s peak.

The Bantam was literally the most popular motorcycle in the world for a while, with 100,000 built by 1953. Works director Al Cave confirmed that 300 a week were still being made as late as 1968, and TCM’s co-founder Bob Currie put the final production figure at over half a million. The bottom line was price; the 1950 D1 cost just £80 including its optional speedo, rising to £95 for the De Luxe with plunger springing plus battery lighting. Bantams were not only cheap to buy but cheap to run, with 112mpg returned at a steady 40mph, significant since wages were low and petrol was still rationed when the D1 was launched – and would be again, briefly, during the 1956 Suez crisis.

But all that would have been no good without the Bantam’s ruggedness and relative reliability, as evidenced by both male and female world travellers’ phenomenal journeys (New Zealand to London, anyone?), by the Competition variant’s success, and by years of daily commuting to work.

D3’s forks had been strengthened from its 1954 start.
D3’s forks had been strengthened from its 1954 start.

However, there were always cries for more power, from the travellers, from those who regularly carried a passenger, and from keen young folk getting their first bike. For 1954, DKW, relocated to Ingolstadt in West Germany, produced a bored-out RT175 (its old factory, the Zschopauer Mottoradwerks in the East, simply reversed its initials to become MZ, and built their own IFA 125 version).

At Studley Road they held off going the full 50cc hop-up. But designer Bernard Hooper, later of Norton Commando fame, and Austrian two-stroke expert Herman Meier, did revise and enlarge the D1 for 1954 to produce the D3. They increased the bore of the 52x58mm 123cc engine to 57mm, giving 148cc. This capacity, incidentally, kept it in the same road tax bracket as the 125.

With increased transfer ports, flywheels of the thicker type only used previously when Lucas electrical equipment had been specified, and a larger 11/16in Amal 523/1 carburettor, the result was a power increase modest on paper, from 4.5 to 5.3 bhp@5000rpm, but with the result of noticeably increased performance. Retaining the same three gear ratios as the D1, a D3 moved up through them in smarter fashion, topping out at 52 as opposed to the D1’s 46mph, with a realistic cruising speed of 40 to 45mph; though headwinds still slowed things down.

There was also, during 1954, a significant improvement to the engine. Up until then the Bantam’s main bearings, when thrashed, could be a weak point, as they had been lubricated solely by the oil in the two-stroke mix. Now there was positive lubrication for the left-side bearing from the gearbox, via drillings in the crankcase channelling oil to the bearing, with a catchment area and a drainway. The right-side crankcase seal was moved inboard of both main bearings and relocated against the flywheel. The left-side seal was moved 0.010in further outboard, the crankshaft being extended by that amount.

Alex Taylor with, finally, a smart ‘unpatinated’ classic!
Alex Taylor with, finally, a smart ‘unpatinated’ classic!

The big end, another D1 problem on long rides, was also uprated, now fitting rollers increased to ¼ x 3/8in diameter, with the flywheel recessed at the crankpin eye to take the larger rollers.

The 1954 cylinder barrel, now with a broader base, and the head, featured more generous finning for both the D1 and D3. The D3 came with plunger frame only, and a dualseat rather than a sprung saddle as standard, both implying two-up capability. The D3’s front forks were strengthened with thicker upper stanchions from the C10L single. Above the forks there was a restyled cowl-type mounting for the headlamp. The D3’s brakes were enlarged from 5 to 5½in.

The same shapely 1¾ Imperial gallon tank now sported chrome styling strips. The filler cap, incorporating a measuring cup for the 20:1 ratio oil, was moved from the left to the right side. The Bantam’s single petrol tap was on the left, and previously it had been all too easy to dump in the measure of oil, and before you’d had a chance to mix it by shaking the tank, find that it had gone straight down into the (open) tap and thence on to clog up the carb. Don’t ask me how I know this…

The D3 led a cleaning up of the original Bantam styling, with its quaint but old-fashioned massively valanced front mudguard fastened to the fixed fork tubes, and its pear-shaped ‘flat’ silencer. The front mudguard, now supported from the lower fork stanchions, was of a slimmer, more conventional style. The rims of the 19in wheels became chromed rather than painted as originally. The silencer was now a ‘cigar’ shape, with a finned tailpiece which could be unfastened so that, usefully, the internal baffles were now removable for regular decoking. But enough traditional features, like the forks’ corrugated bottom-end gaiters, the carb’s circular ‘strangler’ choke/air filter, and the centrally-mounted bulb-horn, remained, making the D3 a reassuring evolution rather than a ‘modernising’ revolution like the new 1965-on petrol tank. And at £102, the new 150 was in the affordable Bantam tradition.

D3 Bantam Major was a bored-out D1, but with strengthened forks, 1956 swinging-arm frame, and more go through its three gears.
D3 Bantam Major was a bored-out D1, but with strengthened forks, 1956 swinging-arm frame, and more go through its three gears.

In 1955, the spacing of the cylinder barrel studs increased to permit a larger diameter barrel spigot. This required a spacing collar between the left-side flywheel and main bearing to be deleted. Like many Bantam developments, the different crankcases and barrel involved were not interchangeable with the previous ones. No one ever promised Bantam restoration would be easy!

The D3 was selling well, and the 1956 season brought a major development, the new swinging-arm frame. Bantam frames had been all-welded from the start, but the new, heavy-duty tube rear section featured brazed lug construction. Weight increased, but not spectacularly, going up from the plunger-frame D3’s 217lb to the swinging-arm’s 228lb. And the price was just £2 more.

With non-adjustable Girling rear units and Silentbloc bushes for the swinging-arm, the new version handled well, with only the continuing low-set footrests limiting cornering angles. Comfort too increased dramatically. The Bantam characteristic of low-speed docility, rare in a two-stroke, was intact, and a new, longer, megaphone-type silencer, still with the finned detachable end-cap, delivered better performance; though at the cost of an exhaust note which a test in The Motor Cycle described as “disconcerting” – a harsh word by the accommodating standards of the 1950s motorcycling press. Styling saw a redesigned stepped dualseat, and the former suspended rectangular toolbox and exposed battery (where fitted) replaced with concealing triangular side-panels, echoing the larger BSA range.

Mid-year, the engine was modified internally. When the stud centres had been widened for 1955 and the spacing collar between the flywheel and main bearing deleted, it was now found there was a need to replace the collar by an oil drag fan to create turbulence for the incoming mixture.

D3 proved well up to the tester’s 14½st – probably the equivalent of two 1950s teenagers!
D3 proved well up to the tester’s 14½st – probably the equivalent of two 1950s teenagers!

A final change would come late in the 1957 season, when the process of improving lubrication to the mains was completed, with the left-side crankshaft seal repositioned inboard of the left-hand main bearing, with a rubbing diameter on the flywheel. An extra seal was also fitted, and both bearings lubricated from a catchment filled by oil from the primary chaincase.

And that was it for the D3, as Bantam development had moved to Small Heath in 1956, and after a stab at a 197cc version (too vibratory), they fell back on the trusted method of – following the Germans. Ingolstadt’s RT175W (for ‘West’) had 62x58mm, 174cc dimensions, while the new-for-1958 Bantam D5 Super featured the not-terribly-different 61.5×58, 172cc measurements.

Accompanied by what Owen Wright in the best book on the subject, BSA Bantam (Crowood Press), called ‘Middle-Aged Spread’, the new 175s were more powerful but less stylish; something had been lost.

D1’s cockerel tank emblem had been simply proudly posed, but D3’s was crowing!
D1’s cockerel tank emblem had been simply proudly posed, but D3’s was crowing!

Bantamite

Due to the proximity of the right footrest and that concentrically mounted kick-start pedal, I let Alex, with daintier trotters than my size 10s, make the two or three gentle prods that it took to bring the D3’s 6.4:1 compression ratio engine to life. I felt immediately at home on the green dualseat, and we snicked down into first and pulled away smartly.

The D3 proved delightful, the comfort and springing a real surprise after previously sampling Mr Taylor’s plunger-sprung D1. The plot was light, and wonderfully docile and unfussy as we circled for the camera on a quiet road. The engine leaked no lubricant, and on modern oil, did not smoke. But out on the A- and B-roads, picking up cleanly and eagerly through the three well-chosen gears to a comfortably brisk indicated 45mph, the little 150 was a real pleasure to ride, and it stopped well too. The high rasp from the silencer was anything but ‘disconcerting’ – it was keenly delightful.

But then, I’m a confirmed Bantamite. I once rode a 175 for a year or so dispatching in Central London, and the worst thing that happened was running out of petrol one time. That was after I’d taken another one down to Italy, shipped out for Greece and then Crete, and after a couple of months on that fine island, sailed again to Corfu, and from there to Dubrovnik and then Venice (on that ship I’d had to push it up the passenger gang-plank – try that with a BMW). Next I rode across Italy to Genoa, and shipped out again to Mallorca where my dad had retired.

D3’s larger 5½in front brake, with new linings fitted by Alex, worked well.
D3’s larger 5½in front brake, with new linings fitted by Alex, worked well.

The only trouble I’d suffered had been a boiled battery up by Delphi; I hadn’t been briefed about the alternator model’s problem of overcharging. Fear of recurrence meant that back on the Spanish mainland, I and the bike took the train from Barcelona to Paris, leaving the City of Light as dawn broke, and due to a traditional lack of funds, riding the 140-odd miles to the Channel port on just a tank of petroil and a café au lait.

As indicated by the electrics, all my Bantams had been late model 1969-71 B175s, the last, and as I considered, best and most practical ones. However, I now remembered the infinitely experienced Bob Currie’s judgement: “But for all the potency of (the late 175), it was a harsher and less forgiving machine than its forebears.” After the run-out on this well-sorted swinging-arm D3 Bantam Major, I think he may have had a point.


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The 1¾gallon 1954 tank’s right side filler cap; with former left side cap, two-stroke oil could pour directly into left side petrol tap, clogging carb.
The 1¾gallon 1954 tank’s right side filler cap; with former left side cap, two-stroke oil could pour directly into left side petrol tap, clogging carb.

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