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No Animals Were Hurt In The Making Of This Documentary

Not a Bantam, nor a Tiger Cub

Ok, let’s get a few things straight before we start.

Firstly, I am a purist, not a pedant.  If you seek proof, witness the fact that I am still seeking original parts for my Gold Star to replace substituted ones I have used to ensure the bike remains usable, and this on a machine that I have owned for more than 35 years and kept in roadworthy condition.  For example, the remote float suspended from a rubber cork has finally been replaced by the correct reproduction hanger.  Similarly, the Italian chrome rims I was obliged to use will be replaced by British made ones as and when they, and funds, become available.  In the meantime, the Italian ones keep the bike on the road.

 Hence, if a genuine part can be used in its original function, it will be used.  If the function requires an original recyclable part to be modified, or destroyed, it will not be used.  An alternative will be sourced or manufactured and the original part offered up to be used as it was originally intended.

Secondly, if you think that building your own trials Bantam from parts is a cheap option, think again and stop here.  Be assured that you can buy a ready built competitive machine for less money than you will spend on the project.  The priceless satisfaction of building it yourself is the only bonus that you can expect.  There will be no financial one.

Still interested?  Then read on.

This is more of an odyssey than a technical article, although I will provide technical descriptions and drawings where possible.  I am not aware of any relevant publications other than two I have used from magazines of the era, neither of which are sufficiently detailed to be of any great use, although they did give me some ideas.

Your best friend is the Internet.  Many parts were sourced from on-line auctions and there is a wealth of information freely available on the World Wide Web.  Links will be provided where appropriate.  Don’t ignore the established businesses though.  Bournemouth Bantams, Bantam John, T and G Motorcycles and local bike breakers all provided items for my version of the project.  All these proved helpful and competitive in their pricing.  Delivery times were fast and information gladly provided.  Details of who and where will be found on the Useful Links Page

The article will be split into component parts starting with:

A Caveat

All the pictures used were taken in real time.  That means that they are mostly of rough assemblies and unfinished components.  They will look better when prepared, painted, plated or otherwise cleaned up.

AND

Basic Advice

Don’t try to build the finished item.  Build it up from parts first then, once you have everything, strip it down, prepare, paint and plate, then re-assemble.  That way you get twice the fun and you don’t ruin your job by careless wielding of an angle grinder or file. 

Choose a standard and stick to it.  I mean, do not use nuts bolts and screws of different forms.  Use either BSF/Whitworth, UNF or Metric in that order of preference.  A job lot of BSF nuts, bolts and set screws provided me with the wherewithal to glue the lot together.  I chose to purchase ex-government unplated items which I cut to size, and the investment of a set of BSF taps and dies along with a plating kit completed that part of the project.  Approximately 50 sets of nuts and bolts in sizes ¼ to 3/8 cost me about £10.00 and were more than enough to complete the project.  OK, I had to plate them but more on plating later.  I also bought some WW sized hexagon bar stock in 12" lengths to make up odd nuts.  This stock is a peculiar size but available from WVS Fasteners. Trust me, it will try your patience to have to constantly seek out metric or imperial spanners according to what fittings you have used.  Most of the threads on the D7 Bantam engines are BSF and earlier ones are Whitworth so you will need Whitworth spanners for both types.  That being the case, use BSF or Whitworth for the cycle parts for the sake of consistency.  I know you can’t pop down to your local accessory shop for the odd nut or bolt, but in the long term it pays to standardise.  I found that keeping every imperial nut and bolt that was not chewed up was a sound investment as they can often be recycled by cleaning up or re-cutting threads, and re-plating.  There is something very satisfying about this, knowing you have saved original fittings from being turned into non-descript parts for the bland generation of metallic bling we are so fond of these days.   BSF and Whitworth dies and taps are comparatively cheap and will repay the investment many times over.  A list of suppliers is available at the end of this article.  Be aware, that this may change, but all were in practice during the lifecycle of my project. 

A lathe, compressor, pillar drill and a welding plant are not essential but certainly useful.  I had all these already, and having bought them some years ago, they have paid for themselves over and over again.  If you have none of these, you can manage, but some jobs are just so easily accomplished with these tools that purchase might be a serious consideration.  My ones cost me about £400.00 in total, but over the years have saved me much more.  Wise buying and patience would reduce this to about £300.00 in today’s auction frenzy world.   Word of warning, though, all of these are potentially dangerous to use.  If you want proof, pop along to your local friendly machine shop sometime and count how many operatives have bits missing from their fingers!

The Frame.

This is where it all starts, and rightly so.  The item I purchased had been butchered beyond road use by having a section of the lower frame cut out, I know not why, possibly to replace a damaged item on another machine. 

The piece removed was the cast sleeve and stub on which are mounted the rider’s footrests so my generous interpretation of its provenance may well be correct.  This along with a swinging arm and brand new but scratched sub frame cost the princely sum of £25.00 on Ebay.  See how easy it is to be lured into a project like this by the anticipation that everything needed will be relatively inexpensive.  Read on and you will find out the truth.  I resolved the problem of the gap in the frame by finding a suitable piece of air tube at the local metal recyclers (scrap-yard).  This needed an OD about the same as the frame tube, with an ID slightly smaller.  It was a simple job to machine the OD of the piece down to the ID of the frame for about an inch either end to make a slug, insert the slug into the gap and zap it with 130 amps of arc from a home welder to make a strong fillet all round.

For aesthetics, I ground it off and finished with a file but as this is hidden under the engine I couldn’t worry too much about how it looked as long as it is strong.

You, dear reader, will not be troubled with such toil, but be aware that the presence of the original sleeve and stubs does reduce ground clearance somewhat, but not critically so if you are not of the ‘Purist’ persuasion, you may wish to remove the footrest stubs but leave the sleeve in place.  Your frame, your choice, your conscience.

 

Next, some surgery.  Remember, my frame was already bastardised so the next bit presented me with no dilemma.  The rear mudguard if fitted to the sub frame loop, cannot be mounted high enough to fit the preferred size tyre (see Swinging Arm).  In order to overcome this, a bit of cut and weld was required.  This is especially easy if you have an old pair of handlebars which are past use as the bend in them is exactly right for this modification and the diameter is right too.  I cut the subframe just behind the strong point where the springs attach and reduced the freshly cut ends of the rear loop by about 4 inches.  I found some tube that fitted inside the now exposed tubes and cut four pieces about 3 inches long for slugs.  I then removed a 4 inch section from either end of a pair of scrap handlebars with the bend nearest the centre of the bars in the middle of the piece cut out.… sounds confusing?  Have a look at the picture with the cut out pieces circled.

All that needed doing then was to slip the 3 inch ‘slugs’ into the ends of the pieces cut out of the handlebars, and then into the two separate parts of the subframe loop and hit it hard with the arc welder making sure the arc penetrates fully.  Having ground off excess, the job is done.  This must be strong as the subframe takes a lot of stress, and it should be ‘straight’.  I know it is bent, but you know what I mean!  If doubtful about keeping it that way, the whole lot can be bolted down to something rigid like the kitchen table but in all honesty, I found it easy enough to get it straight at the fabrication stage before welding in anger.  Photograph might help.

 

Swinging Arm

Easy peasy this.  The choices are simple.  Use an original Bantam one with a WM2 rim  and a 3.50 X 18 trials tyre (A WM1 will JUST work).  Beware though, that this size tyre is not commonly made by the big players so a Chinese copy might be the way to go.  A standard 4.00 X 18 will not fit as it fouls the right hand leg.  The better solution is to fit a later Tiger Cub swinging arm which is wider on the right and, believe it or not, is a direct swap.  See them together making it clear that the one on right the is the wider Tiger Cub version.

I bought one for £25.00 and it fitted straight on. It has the advantage of being marginally longer. All the wheel spindle fittings are the same so it really is a straight swap.  A powerful press (not a lump hammer!) is essential to press the spindle in and out.  The 400 X 18 tyre with a WM3 (2.15) rim should fit this arrangement.

 

Front Forks.

This is where I expect much sucking of air through teeth, shaking of heads and comment from the pedants.  Clearly the Bantam forks of the era, although entirely suitable for their intended original  purpose are inadequate for this one.  Quite simply, they will bend and are not long enough to accommodate the obligatory 21” wheel.  The favoured option is to fit a set of later B175 or Bushman forks, commonly known as ‘Heavyweight’.  I am all for this, but have you heard of the expression ‘Hens Teeth’ or more commonly, ‘Rocking Horse S**t?  Well these are about as common as the said forks.  So it was off to the breakers with a tape measure and sufficient beer tokens to grab the attention of the man with greasy overalls and a roll-up permanently fixed to his bottom lip.  If you want to follow the same tactic, here is my solution.  I found a drum braked Yamaha DT50 amongst the detritus (sounds of teeth sucking from the crowd!) and removed the forks, wheel, yokes, hub, in fact everything in front of the headstock and got a price for it.  I found one with a decent tyre as a bonus.  I didn’t bother with the handlebars and control levers, they are just too bling for the purpose.  If you intend to follow this path, about 50 beer tokens should cover it, and push your luck a little by asking for a pair of footrests to be thrown in for ‘good will’.  You never know, even bike breakers have a sense of humour sometimes!  You will gather that the above items are very easily modified for our purpose, and are very capable of accepting the sort of punishment you are likely to inflict during a pre-65 or twin-shock event.  The forks I bought had a longer headstock than the Bantam one but the bearing races were interchangeable with the Bantam ones.  Actually, not quite interchangeable, to resolve the longer headstock problem, I needed to machine two spacing adapters, one for the top and one for the bottom of the headstock (Praise the lathe).  These sleeves should be a press fit at one end into the Bantam headstock and a new bearing housing machined into the other end.  These two housings were made to fit the existing races which were very slightly different, one being metric, the other imperial.  If you are intending to follow this line yourself, the drawings may help but you may need to amend the dimensions slightly to suit what you have.  Once fabricated and tapped(?) into place, I made sure all was square and spot welded the adapters in.  Ah ha, you say.  He’s destroyed the frame now in spite of what he said.  Actually, the frame was already destroyed from a practical point of view but in any case, this adaption is not permanent as the welding could be ground away and the adapters removed at some time in the future if required. Here is what it looks like.

I think you will agree this is not a difficult adaption.

For the teeth suckers amongst you, please bear in mind that cannibalism was a practice followed by all the works teams from the dawn of civilisation to this very day.  Trials bikes of the pre-65 and twin-shock era were very much ‘bitsa’s’ with components cobbled together from many different sources.  In particular, the Triumph/BSA/Ariel triumvirate were past masters at it.  All I have done in using Yamaha forks is to bring the practice into the twenty first century.

 

Wheels and Suspension

So by now I had a front wheel, forks and a frame in a cohesive lump so I needed a rear wheel an engine, fuel tank, seat, exhaust and all the other bits to make it work.  This was a sticking point for me as there were no such items on the horizon.   I took a chance and bought a ‘project’ bike for £100.00 again from your friendly internet auction site.  This seemed to be a frame, two engines, wheels, mudguards, tank, seat in fact enough to build a complete bike with bits left over.  Condition – parlous, location, North Wales so another £100.00 was paid for delivery.  I was somewhat disappointed when it arrived as it was doubtless worth the £100.00 I paid for it, but the delivery charge really made it less than a bargain.  However, too late now and a quick sort out resulted in summary disposal of the fuel tank, seat, one set of crankcases, both wheels, but keeping the hubs and brake assemblies along with a record of the offset…you will need this when you get to the rear wheel stage, a piston, and all of the electrics.  All the chewed up nuts and bolts were immediately discarded.  I kept the studs as these can be recycled into shorter ones with new threads.  The rear wheel was likely to be an expensive item.  One cannot be obtained from the breakers cheaply unless you are extremely lucky, most breakers are very aware of how rare good Bantam wheels are, consequently, how much they can get for them, and to use one from a different machine will involve all sorts of difficulties with chain alignment and size.  In the end, it might be necessary to buy a new 40 hole WM3 (2.15) or WM4 (2.50) rim and have it built onto a hub, several of which are frequently available on Internet auction sites (presumably because their parent rims and spokes have long since rusted into oblivion like mine had).  This rebuild will cost about £150 - £200 depending on the quality of rims.  See, not such a cheap project after all.  Having said that, you might be lucky like I was.  I managed to buy a decent 2.50 X 18  X 40 hole rim for £10.99 from an Internet auction, reclaim the spokes from one of the rusty Bantam rims I had, and rebuilt it having re-plated the spokes myself.  Experts will tell you that wheel building is a craftsmans job for them alone.  My version is that if you have a wheel to copy, you can re-spoke a rim yourself.  It’s quite simply a case of copying the pattern from one to another, and then tweaking the spokes to make the rim concentric with the hub, creating the correct offset and finally truing it up laterally.  If you are confident enough to be taking on this entire bantam project, the wheel rebuild will be within your capabilities.  The alignment of the rear sprocket and engine sprocket are not affected by the wheel building process as the hub position is determined by the clamping within the swinging arm.  Thus, if the offset has been measured correctly in the first place, and replicated, all will be well.  In fact, even if the offset is marginally out, it can be corrected by pulling the wheel one way or the other by tightening and loosing spokes. 

Rear springs and shockers are also available from about £10.00 upwards for a pair of serviceable units.  Take them apart, scrap the covers and paint the rusted chrome springs red…everyone else does, so I did too!

 

Seat and Tank

Fuel tanks are available from same Internet auction site.  I chose to use a Bantam D7 one rather than a pukka trials type one as I think it looks good, is cheap (about £15.00 including postage) and is more like what the riders of yore would have used.  A scruffy old seat can be sourced similarly and modified to suit by cutting off the back half and recovering with a proprietary trials seat cover costing about £20.00. I did something different though.  I made a base from GRP having created a female mould from hardboard and gaffer tape.  Its actually quite easy. The base being flat I cut a piece of hardboard to shape then some narrow strips about 2 inches wide and fastened these at right angles to the top with gaffer tape.  I then filled the inside of the joins with silicone to give a reasonable finish and laid up this female with GRP mat and resin, having polished with release agent.  I bonded in two strips of scrap steel at the front and back so I would have something to screw the fastenings into later.  Two layers of mat are plenty for the base.  For foam, I bought a camping mat from the Pound Shop and cut several layers slightly oversize and glued them to the newly made GRP base.  I then bought some vinyl, not the ordinary sort, but the sort that stretches in all directions and following the instructions covered the foam and riveted the cover at the back.  This last part requires patience and a warm day but the end result is well worth the effort.  This lot cost me about £20.00 all in and there is enough cover material, GRP mat and resin left to make at least another two bases.  Indeed, I made the frame side panels and still have enough left for at least one more seat.  Have a look at the finished item and compare it to one costing four times as much from a dealer which will be of the universal type, described as ‘fits all’ but in reality fits none.   Supplies of cover material and instructions can be had from Saxon Seats .

 

Exhaust

This had to be fabricated although the original Bantam high level version was a good starting point.  A trip to the breakers provided a silencer of dubious ancestry which looks the part and as everything can be sprayed black, chrome is not an issue.  Neither is performance so anything that helps avoid the wrath of the ACU sound inspector will do.  I should know, I am one….!  I obtained a Suzuki rear silencer for £5.00, a Bantam high level pipe for £10.00 and £9.00 for the joining piece again from the on-line auction site.  At first I thought it looked odd but having studied period pictures of the Wassell bantam built for the still-born 175 Trials championship, I am happy that mine fits the bill aesthetically.

 

Engine

Here I had a bit of luck, well maybe, I haven’t run it yet!  I had the offer of near complete D7 engine from close by in Cornwall.  I already had enough parts to build an engine but the offer was too good to miss, and I reasoned that I could flog off what I didn’t need later, hence justifying the purchase.  (Now where have you heard that one before?)  OK, deed done, engine purchased.  I needed a few bits and bobs, generator bush, piston rings, gaskets etc and these came from T & G Motorcycles who were exceedingly helpful on each occasion I displayed my considerable ignorance of things Bantam.  I was reliably informed that the three speed engine in standard form is perfectly OK for trials but the proof of the pudding……!  A real sticking point for me was the kickstart.  It needed to be folding but such items secondhand are very rare and I really was not prepared to pay the price for a new one.  I had a non-folding one from my original purchase so some ingenuity was deployed.  Heard of Pit Bikes?  Well, they are Chinese machines of dubious quality much favoured by paddock kiddies, and scorned by adults.  I bought a new kickstart for one of these for £7.00 (you can judge the quality from the price), cut off the folding parts from it and my original one, and welded the two together with enought amps to light up the street.  Job done and the bonus was the bit left over from the pit bike item fits perfectly on the gearbox splines to make a very fancy chrome gear change lever.

 

Cycle Parts and Controls

Standard 7/8” bars are de rigeur and readily available.  For the classic look, I chose to use chrome with a welded in tie bar but there are plenty of modern ones in the breaker’s yards in every colour of the rainbow.  You pays yer money…..etc.   Similarly control levers.  I like chrome ones, but you can use any really.  Most of the ones in the breakers have switchgear attached which I think look wrong on a classic trials machine, and the wealth of dealers available who sell pattern classic items made the choice obvious, to me, anyway.  Cables were all home made, or adapted from existing ones.  Unsolder the nipple, cut either the outer or inner to size and solder nipple back on.  If you prefer new, all the makings can be readily bought and made to fit.  If you bought a lathe, you can even make your own nipples from old brass screws…. See, told you a lathe would pay for itself.

The rear brake pedal was simplicity itself.  It was made up from bits of scrap steel welded together and pivoted on a machined spindle.  The plates were cut from some scrap 1/4 inch alloy plate and bolted to existing mountings.

 Mudguards 

I nearly sold my soul here.  I wanted period aluminium ones, just like the ones I bought from Pride and Sharks in the sixties for 17/6!  Not a chance.  Such items are unobtainable for anything like the price I was prepared to pay.  A quick flick through the pages of WWW found a compromise in pairs of grey plastic replicas for around £20.00.  I recall seeing these fitted as standard to OSSAs of the seventies so justified them in that way.  In any case, they are much more practical than aluminium which always gets dented and split with vibration.  To fit them, I fabricated (bent) two strips of steel bar to the shape of the forks and welded them on at right angles.  When drilled, they provide ample fixing.  If you choose to do this, be careful with the welder.  If you blow a hole in the fork legs, you will be going back to the breakers for a replacement set.  They rely on being airtight to work!  Hoops and brackets to fit the guards to the forks were easily fabricated from flat bar and alloy tube from the local DIY shop, with end fittings turned down (in the lathe by chance?) and glued in to the tube.  This picture should make it clear.

 

Electrics – A Necessary Evil

I removed all the wiring except for the connections to the points and condenser.  A poster on the Bantam Forum advised me that all I needed was a stator mounted ignition coil, pattern versions of these are available on your favourite Internet Auction site, with an HT lead soldered directly on to it.  This is what I have done but haven’t yet tried it in anger.  There is certainly no spark in evidence from a gentle kicking over whilst out of the frame but with a size 10 welly behind it, who knows?  That’s it for electrics…. Simple or what?  Actually, no.  Every Bantam engine I have seen has had a severely worn olite bush in the stator plate.  Wear here causes the end of the shaft to whip and plays merry hell with timing and spark production.  It needs to be replaced at the grand cost of about £2.50.  Care is needed to drift it out but it will certainly need doing.  Because the bush housing was oversized on my engine, I actually made mine, (cue lathe) from a bit of phosphor bronze obtained from the scrapyard for £5.00.  My £5.00 investment will make about a dozen similar bushes.  Most recycled stator plates are distorted at the edge as a result of overtightening the securing screws.  I bought several, none of which cost more than a fiver and when I received them, I found out why they were so cheap…distortion.  These can almost always be salvaged if you have access to a lathe.  Simply clamp the distorted stator plate to a faceplate, points side towards the face plate, and take a light skim at the edge.  That’s what I did and the fit is perfect.  Another valuable piece of kit salvaged.

 Its Play Time….nearly

Except we need to start all over again…. Almost.  All the bits are there and should amount to a cohesive if unsavoury whole machine.  It all has to come apart at this stage, and I mean apart.  The frame can be salted and peppered to taste.  Powder coating is durable but unattractive (I think).  Hand painting is a messy and unprofessional business unless carried out by a time served professional, leaving a spray job as the option.  I sprayed…using extremely toxic two pack which you can only purchase legitimately if you are qualified to use it and have the correct facilities.  So let’s pretend I satisfied these conditions and assume I have the paint.  Spraying was done outside on a warm day, using the compressor (remember you finally decided it was a worthwhile investment).  I did the frame swinging arm and fork legs as well, all in black and a very nice job it turned out to be.  I suppose a lecture on preparation would be out of place here?  I also two-packed the tank and side panels after three coats of primer filler.  I am assured by the man at the paint suppliers that the standard respirator (mask) they sell for a little over £20 is perfectly OK for spraying two pack as long as the instructions are followed.  I did, so I did, so to speak.

 

Now, for plating.  My pet hate is rusty nuts bolts, screws and the like.  I paid out £50.00 for a home plating kit, again from an Internet auction site.  I had my doubts but these were dispelled at the first attempt.  It worked and I treated all the old rusty and unplated fastenings to a coat of zinc plate and they look like new with just a slight patina of age.  Money well spent.  Of course you can buy new fastenings if it suits you and your budget but £50.00 won’t buy many fastenings, and my plating kit will still be good for hundreds more similar long after the Project Bantam rolls its wheels in anger.

 

Odds and Sods

Now clearly this is just a short version of the build process but I believe it covers the major points.  Many bits and pieces will need to be bought or made to finish the build.  However, most of these  are readily and cheaply available. For example, a suitable 415 size chain was purchased from Trials Bits for around £7.00, brake shoes are standard Bantam items, rear brake lever and mountings were made from bits of scrap steel and aluminium.  Bushes and spacers were made up as required.  Footrests were bought from a seller on Ebay.  A side stand was made from a Jailing one bought from the breaker for a fiver.  The bash plate cost £11.00 and was originally from a Pit- Bike.  Chainguard was from a CG125.  The list goes on.

 

If you need convincing about the availability of bits for such a project, go to the EBay site and type BSA Bantam in the search box…..

  

Final Stages.. at least it's starting to look like a trials bike now.

  And then it was finished.........take a look.

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