Hi all. I’ve recently read a couple of RetroRider’s motorbike threads, and thought I might add one about the two Bantams that occupy my garage. I’ve had the first one, a 1953 rigid D1, since February 1978, so forty two years now. The lady who owned it before me bought it new. Back then, the idea she'd owned it for nearly twenty five years was staggering to me. The fact that I've owned it fast approaching double that is quite sobering; makes me feel old!
This is a pic of me on it, probably around the summer of 1981:
Back then it was still completely original, although very worn from being used daily for commuting and covering 30,000 miles or so; maybe more, the speedo didn't work. Neither did the lights, although it started well it rattled really badly.
Like most kids, I thrashed it, fell off it, bent it, straightened it, modified it, broke it, fixed it, ignored it, rediscovered it, got frustrated with it and so on in a never ending loop. It had its 125 cc engine rebuilt before I left school, with a rebore and all new electrics, flywheel rotor, stator, coils the lot; but it always played up. Usually running fine for about forty minutes or so, then needing a rest. About thirty four years ago I fitted a battery/coil ignition D7 engine which ran well and gave an easy 50mph cruise. That stayed in for a decade or so until I pulled it out for a D5 green-lane hybrid I built (another story). The 125 engine went back in and continued to muck about. Every now and then, generally when between bigger bikes, I'd do a bit on it in a fit of enthusiasm, but the frustrating running issues never stopped.
In 1998 I took it with me in the back of my lorry whilst working for Yamaha doing promotional work across Europe. I got to ride it (slowly) around most of the major European race circuits: Donnington Park, Brands Hatch, Jerez, Catalunya, Misano, Monza, Mugello, the A1 Ring, the Nurburgring (the GP circuit, not the old ring), Sachsenring, Poznan, the Hungaroring, Paul Ricard, Assen and used it to go shopping in all sorts of places. I pushed the damn thing in almost every country in Europe!
After another lull, sometime around 2006, I built a second early D1 engine up using a set of period tuning notes; stuffing plates in the cases, enlarged oilways, matched and enlarged transfer ports, cutaway piston, skimmed head. It ran well, but was really peaky. It couldn't get over the huge gap between second and third. I tried a close ratio gear set, but that made pulling away and slow traffic tiresome. And it still cut out when hot. So I pulled it out, flogged the tuned engine on in disgust, and put the original back in. Which continued to frustrate.
I finally had a eureka moment. Reading in an old article cut from a 1950s magazine, someone had suffered similar issues and it turned out to be a mis-machined generator rotor. Apparently, the magnet placement, relative to the keyway for the camshaft, is pretty critical. The points need to open at, or fractionally before, the point where the magnetic field is at its peak. If the keyway isn't in the right place, the field will be collapsing or worse, non existant when it's needed most to generate a spark. Symptoms are poor running when hot, poor running unless points gap is closed down from the book 0.015" ( mine needed to be 0.010" or less) and poor starting. Apparently both Wipac and BSA knew about this, and offered a special profile cam to cure it. Checking my (not really NOS anymore) flywheel against some older ones I had in the shed showed clearly that the magnets were about 15° out relative to the keyway compared to the others. Over twenty years of mucking about and it was one of the "new" bits at fault all the time! I changed the rotor for one of the others in my store and went for a ride. The bike then ran without issue. The swine!
It was, however, pretty sluggish compared to the D7 engine. Not wanting to go that route again, and having learned the hard way the futility of going too far down the tuning road, I settled for just fitting a head from a later big-fin 125, trimmed and shaped to suit the early barrel, skimmed 0.100" to raise the C/R and with a slight squish to the combustion chamber. It ran pretty well then. I've subsequently fitted a Rex Caunt generator/cdi ignition/lighting system which gives much better starting and running as well as lights that actually work.
It's still not getting much use, but at least it goes when I want it to these days. It looks like this now:
The later forks have been on there since I fell off it in 1992, bending the (already straightened once) originals beyond repair. I have the correct type, just haven't found the time in twenty eight years to strip, paint and fit them! The black tank was the idea of a teenage me; a style trend the middle aged me no longer approves of.
I quite fancy the idea of a cosmetic overhaul. The cost and effort puts me off. The bike has been running and rideable for nearly all of the (almost) four decades it's been in my care and I know if I disassemble it for paint etc. it'll likely be in bits for ever.
Current plans involve replacing the battery (which is always flat) with a capacitor hidden in the toolbox and simplifying/tidying the wiring, painting and fitting the right type of forks, and rebuilding the engine internals into a set of 150cc D3 cases/head/barrel I have to give a little more go without the loss of flexibility that tuning the 125cc engine resulted in.
The other bike is a more recent purchase. In the summer of 2016 I fell over a 95% complete 1956 D3, which is visually the model of Bantam I like the most. They have all the styling cues of the earlier bikes, but with a sturdier swing-arm frame very reminiscent of the B31/B33 singles of the period.
The engine was just a pair of empty cases and a barrel, but they’re the ones that are destined for the D1. In my spares hoard I have a 1969 engine from a four-speed D14/4. I bought it when I was still an apprentice in 1988 I think. Anyway, it was originally intended for the D1, but I realised a long time ago that the D1’s lightweight rigid chassis isn’t really the best place for a peaky 14hp late engine, and it’s been in bits under the bench waiting for a suitable home ever since.
Both these little bikes bikes are real “back burner” projects, and only get a bit of attention when I’m either between jobs, when I fall over parts, or when I need a bit of escape from stuff that’s bogging me down. In the time I’ve had it I’ve not done much. Initial assessment showed it to be surprisingly complete and other than the obvious cosmetic challenges not really needing that much actual repair. I’ve stripped and painted the front wheel, and stuck a new tyre on, and repaired a crack in the footrest/stand mounting area. My plan is to build the bike the teenage me wanted, so to go with the late engine it’s going to have a set of ace bars (ones I had on the D1 briefly when I was 18) and some competition footrests, and be styled as a little cafe-racer. Cosmetically it’s staying as it is. Oily-rag is the order of the day. I'm possibly going to paint a tank properly for the D1, and if I do, then the D1’s tank I painted black while I was still at school can go on it.
Here’s the welded frame repair:
And with a coat of paint:
Since then I’ve not really done anything beyond hunt around for the missing bits I need. I’ve picked up a suitable speedo, a dualseat, some wiring and switchgear. This year’s unexpected progress on other projects means that maybe this winter will see a bit more Bantam activity. Whatever, if I actually manage to achieve anything on either bike I’ll post it up.
All the best, Glen.