Building a comp' Bantam replica

The first motorcycle I was allowed to take the controls of, was an off-road Bantam with alloy mudguards and two-tone paint made up of Fordson blue and mud. It really looked 'the part' to my young eyes. I could not imagine a more purposeful machine. My brother, Chris, who is 7 years my senior, brought the 'bike home and I was allowed to sit on the tank and 'steer' while he sat on the saddle behind me. We sped across a nearby field and another motorcyclist was born. The little Bantam episode spawned many enjoyable years of motorcycling and the memory eventually faded into insignificance, as I sampled the pleasures of all manner of 'bikes from England, Japan and Italy.

The Bantam memory came back to me while I was attempting my first real restoration project. I had 'rebuilt' many motor bikes, and it was while I was suffering a costly rebuild of my Guzzi V50 ( the gearbox had seized ) that I was inspired by the thought of a cheap and cheerful Bantam Restoration.

I had already got the remains of a 1958 Bantam D1 which had lain in my shed for many years. I convinced myself that it would be a cheap therapy after the expense of the Guzzi rebuild. Of course, it was to become an obsession; this bit doesn't go with that. They didn't use those in 1958 did they? It was while searching out all the little detail bits and pieces and scouring the autojumbles for those 'original' bits, that I decided that it would be nice just to construct a fun Bantam from whatever bits and pieces I had left over.

After the '58 D1 was finished, I had plenty of parts to choose from. It's uncanny how the best autojumble finds turn out to be for completely the wrong model. My plan was to use up all the leftovers and produce a machine which I could just enjoy without having to worry about authenticity.

The infant project really received a boost when I stumbled across a pair of 19" trials tyres at Roy Pidcock's shop in Derby. The inventory now consisted of a fully painted tank, ( the filler cap was on the wrong side for a '58 model ) a pair of heavyweight forks, a headlamp, (wrong for '58 ) a D3 engine in pieces swapped for a vintage rear light, a toolbox ( wrong again! ) and a rear wheel hub. A trip to the Classic Bike Show at Stafford left me highly impressed with Chuck Ham's brace of comp' Bantams and I was hooked. My 'fun' project had just turned into another potentially expensive obsession. After spending more money than was sensible on my first Bantam restoration, I determined that this one would be built using ingenuity rather than cash.

A 1954 frame soon turned up, and I was able to start work on deciding what a Competition model Bantam really should look like. Even Roy Bacon's excellent 'BSA Singles Restoration' was a little sketchy on the comp' Bantam front ( the rear as well! ). Obvious differences were the blade mudguards, the decompressor cylinder head, the raised seat and raised footrests.

I advertised in vain for help with parts, but Francis Chamberlain from Norfolk kindly sent me a roll of film showing his own 1949 model. This was the most help I got in my quest as it looked like no original parts would turn up. As is often the case, I bought some plain mudguard blades from Renovation Spares and the next autojumble turned up a brand new, genuine front mudguard still in brown paper wrapping. This saved a great deal of work on my part as I only had to make stays for it. The rear mudguard was modelled on Francis' photographs with stays bent up from 1/2" diameter tubing. The special extended chain guard was made from a road version with a piece of steel filing cabinet welded to it to prevent tyre borne mud from reaching the chain. Things were beginning to take shape.

It was clear that a road model centre stand would not do. Scouring autojumbles with tape measure in hand only revealed ordinary 'short' stands. I reckoned I needed an extra inch of height to cope with the big tyres. Pondering the matter in my workshop one afternoon, my gaze fell on an old Rickman rear carrier. Using the road D1 stand as a pattern, I was able to draw up my lengthened design. After several hours of sawing, turning bending & welding, Derek & Don's Honda carrier had been married with workshop scrap to become a 1954 comp' Bantam centre stand!

The footrests, it transpired, were both left hand ( or was it right? ) 'rests from a BSA C11, mounted on a 7/16" hexagon bar. The bar was prevented from turning by a pair of brackets which fitted between the frame and centre stand. The brackets locked against the already overworked centre stand stop plate. ( yes that bit that wears out, leaving the poor old Bantam listing precariously at the road side! ) These plates, although performing a simple function, had the additional complication of a 7/16" a/f hexagon hole through their centre. I had to resort to some second-form school geometry to mark this hole out and spent an interesting morning with a piercing saw making the holes in two pieces of tough EN8 plate. High tensile hexagon material was used for the footrest bar in the hope that the extra tension achievable would allow the footrests to stay put if knocked about during vigorous posing.

Raised footrests necessitate a higher seating position and this is achieved by mounting two raisers between frame and saddle. The raisers were sized by scaling their dimensions from photographs and were made up by welding as I didn't trust my riveting skills. The saddle mounting looked and felt precarious but combined with the raised footrests and wide B40 handlebars, delivered a regal riding position compared with the low-slung road model.

The whole plot was now beginning to look a bit like the real thing. A suitable rear number plate was turned up for £1 at Newark. A 58 tooth rear sprocket in original paint cost a little more. I built the wheels up with rims and spokes from Central Wheel of Water Orton. Wheelbuilding is one of those rare skills that one can practise without fear of ruining the job. All you waste is time! If the whole thing goes wrong you can take it apart & have another go. If you still can't manage, you can always take the debris back to the professionals to sort out!

Paint work was done with cellulose in my heated outdoor workshop ( the back lawn at the height of summer! ). Colour was dictated by the surplus D1 tank, so not only was this D3 pretending to be a comp model it was also masquerading as a D1, in mist green. I used a small 1/4 litre spraygun attached to a Machine Mart 3.5 cfm compressor. The small gun is ideal for motorbike work, making it easy to spray frames and other awkward parts. Lining was sprayed on after masking up with 3M fine lining tape. This tape is much better than conventional tape, and at only 3.5mm wide it can be guided around quite tight curves. Once applied it can be backed up with ordinary 1/2 inch tape to mask off the areas to be protected.

Unity Equipe made a silencer to order, but were unable to bend up a pipe without a pattern. In the absence of a suitable pipe to work from, I eventually bent (crumpled?) my own pipe from a standard D1 exhaust with a slightly different style from the original. The engine was rebuilt with a new set of gaskets and seals and the remains of a £10 autojumble unit. The head was from a D1 so the combustion chamber was reprofiled, by mounting it precariously in my 1930's lathe, to clear the larger D3 piston. Compression ratio is now nearer 9:1 than the original 6.4 and gives the exhaust a healthy pop when the engine is kicked over.

I had given up hope of finding an original exhaust pipe when one called out to me from under a pile of junk at Cheltenham autojumble. I could hardly contain my glee when the asking price was only 50 pence. Admittedly, it had seen better days, but I now had something for the professionals to work from.

Having been ignored by countless sleepy motorists on much larger machines, I like to make sure that a bike's lighting equipment is up to scratch. On trying the Bantam for the first time, the lights, even with a brand-new flywheel mag, were dismal. The original S55 Mk8 generator is rated at only 30 watts but it is quite difficult to obtain 6v headlamp bulbs that consume less than that on their own. Add in a suitable rear light and the legally required stop lamp and the direct lighting system was in real trouble. I decided to attack the problem with some modern technology by converting to 12v. The main question was; could that little generator provide 12v? It succeeded in lighting a 50w 12v bulb with great enthusiasm, so the earth connection was removed from the S55 mk8 and two wires carrying the a.c. were taken up to a modern solid state rectifier. ( ú2 from the local electronics shop ). A 12v zener diode cost rather more, but both were hidden away on an alloy heatsink under the petrol tank. Battery back up was provided by a small Yuasa sealed lead-acid battery secreted away in the toolbox.

The willing little generator now supplies a 40/50 watt headlamp, 21/5w stop/tail lamp and a small electric horn with no complaints. Just think how much happier we would have been If Joe Lucas had come up with Zener diode voltage control in the 50's.

RIDING THE BEAST (Fowl?)

With its B40 handlebars, big tyres and raised riding position, the comp' Bantam feels more of a man's (?) machine than the low slung standard D1. The 58 tooth rear sprocket allows the bike to run down to a slow walking pace in first gear while top can be engaged at 20 mph or so. With such low gearing the 3 speed gearbox feels less of a handicap. Compared with the road D1, the machine feels almost sprightly. Once top is engaged on the road, there is little need for any other gear. The Unity Equipe replica silencer does little to pacify the neighbours and emits quite a healthy crackle.

Having built the bike, I am now not sure what I want to do with it. The most excitement it has delivered to date was on the way to the MOT test. I arrived at Barrie Rodgers' with the speedo needle trapped under one of the dial mounting screws. Only rapid work with the blunt screwdriver-end of my authentic plug-spanner enabled us to keep our appointment.

After almost 30 years though, the Bantam does nothing to re-kindle that first ride around the field. That was pure magic for a youngster and never to be equalled. Our nostalgia trip has been a mystery tour to nowhere. This machine is a slow, noisy two stroke, just the same, but I can't really get any excitement out of it. It really is no good going back. How about a Matchless G80CS?

Bulbs, Wire & Connectors
Merv Plastics, Nottingham - 01159 9305454

Zener diode
Local Brit bike shop - Mine came from Wilemans in Derby (about £15).

Rectifier and Battery
Maplin Electonics 01702 554161 -
Order code BH48C at £3.95 is a 25 amp bridge rectifier with standard spade connectors

Reference Material
from Amazon.co.uk

Roy Bacon is one of the leading writers on Classic British Machinery. His books are well written and contain masses of information, illustrations and pictures to help with restorations.

Illustrated BSA Buyer's Guide by Roy Bacon

BSA  by Roy H Bacon

BSA Gold Star by R. Bacon

BSA Gold Star and Other Singles by Roy Bacon

BSA Singles Restoration by Roy H. Bacon

BSA Singles Restoration by Roy H. Bacon

BSA Twins and Triples by Roy H Bacon

BSA Twins and Triples by Roy H. Bacon