PUBtalk ...................................................... 102

PUB is in anorak mode over BAPs. Not that sort, but Bur­man BAP gear­boxes…

Real Classic - - Contents -

Speak­ing of gear­boxes, Jac­que­line Bick­er­staff waxes lyri­cal herein about Bur­man’s BAP box

This col­umn is be­ing writ­ten only shortly af­ter last month’s, which means that not very much has hap­pened ei­ther. In­deed, less than one might have thought be­cause ‘the Beast from the East’ hit Great Britain (and that is not an ep­i­thet for Vladimir Putin) tak­ing tem­per­a­tures down below zero in the day­time, and dis­cour­ag­ing any work in un­heated garages or sheds. Some read­ers in un­friendly climes may be unim­pressed, but that is cold for the UK Mid­lands. It is just as well that it didn’t ar­rive a cou­ple of weeks ear­lier or PUB might still be on a for­lorn Welsh hill­side! It did not seem so at the time, but the Dragon weather was ac­tu­ally be­ing kind.

How­ever, smaller jobs can be done in­doors in win­ter, and one such had been to as­sem­ble a gear­box for the pre-war project. This pile of parts (if not pile of poo) in­cluded parts from more than two Bur­man dis­man­tled BAP gear­boxes – save that there was only one out­put sleeve gear be­tween the two. There were also two of the dou­blegears, both of which had a tooth miss­ing, but re­place­ments had re­cently been sourced so a build could be­gin.

Bur­mans are fairly tough boxes, and do not usu­ally need shim­ming or ad­just­ing, so should be fairly easy to as­sem­ble – bar­ring wear. It would ap­pear that those bro­ken teeth were the rea­son for dis­man­tling, for the rest looked gen­er­ally pretty good, al­though PUB did try a lit­tle shim­ming to min­imise end floats as she re-used the old ‘top hat’ bushes, and there was a lit­tle wear of the top gear dogs (even­tu­ally this proved a mostly wasted ef­fort). A new out­put bear­ing was re­quired, as nei­ther orig­i­nal was present, and it is an awk­ward size, be­ing 72mm out­side and 1.5 inches in­side, but th­ese are read­ily avail­able from spe­cial­ists such as Dra­gan­fly.

The ini­tial build-up, how­ever, re­sulted in a very stiff gear­box, even with oil added to the grease as rec­om­mended by Bur­man (Dra­gan­fly can sup­ply a spe­cial liq­uid grease in­stead). Given that there was no guar­an­tee­ing that the var­i­ous parts (even to the case and its cov­ers) came from the same orig­i­nal box, a lot of ex­per­i­ment­ing was called for. Each ex­per­i­ment was both­er­some, be­cause Bur­man use loose 3/16 x 3/16 rollers on the se­lec­tor shaft, and th­ese are tricky to in­sert (and get lost eas­ily if dropped, as in­deed hap­pened to a cou­ple). For some pur­poses the rollers were missed out, as the shaft is a very close fit in the sleeve any­way – but this proved to be a mis­take, as men­tioned below. Note that Bur­man them­selves re­alised the rollers were awk­ward to work with, so some boxes (es­pe­cially WD CP boxes) omit­ted them, by re­plac­ing the roller outer with a fit­ted bronze sleeve in the in­ner cover in­stead.

Even­tu­ally, and with grease ev­ery­where, it be­came ap­par­ent that the gears only tight­ened when the se­lec­tor shaft and those rollers were in place. Eye­ing up an as­sem­bly on the bench, the gear­shaft and se­lec­tor shaft did not ap­pear par­al­lel, con­firmed with a vernier cal­liper. One of the se­lec­tor forks was bent and bound up when the shafts were held par­al­lel in their bear­ings. A bit of work with ‘Son of Thor’ ap­peared to sort that out, and on the next as­sem­bly the whole in­side sec­tion as­sem­bled up and spun freely – hooray. But it was a cel­e­bra­tion too soon.

Next step was to as­sem­ble the outer case and pos­i­tive stop mech­a­nism, but when tried it didn’t work ei­ther. Boo. An in­ves­ti­ga­tion showed that one of the springs in­side the pos­i­tive stop box had col­lapsed and was not do­ing its stuff. A re­place­ment was stolen from the re­main­ing spares – but al­though the pos­i­tive stop was re­stored, the changes were un­duly stiff in the higher gears. Boo again. This was turn­ing into a night­mare, and the whole box was com­pletely dis­man­tled yet again, spread­ing more grease ev­ery­where (bench, tools, over­alls, PUB’s per­son, tow­els, etc.).

Yet more tri­als even­tu­ally re­vealed a bent se­lec­tor shaft too, a sur­pris­ing find­ing as it looks pretty sturdy, but as it stiff­ened up in its bear­ings even with noth­ing else in the box there was no doubt – pre­sum­ably one of those bro­ken teeth caused all this havoc. Once again, a re­place­ment was found in amongst the spares (for­tu­nately with­out rob­bing the sec­ond gear clus­ter) and cleaned up. The straight­ened se­lec­tor fork was also dis­carded at this point, and purely for­tu­itously a NOS out­put sleeve gear had turned up in the mean­time, so it was used and all pre­vi­ous end-float checking had to be re-done! Mean­while, new pos­i­tive stop springs had ar­rived from Dra­gan­fly, who have a good se­lec­tion of the stan­dard parts for BAP and CP gear­boxes. Th­ese new springs were much stronger than the soggy old ones, and were dif­fi­cult to wres­tle into place. In fact one pinged across the garage and proved very hard to find. Even­tu­ally, an ap­par­ently work­ing gear­box was the re­sult – hooray again (and hope­fully for good this time).

Sadly, how­ever, al­though this BAP is quite use­able for the project, pro­vid­ing ra­tios that will be suit­able for rid­ing on the road, it is not what the bike prob­a­bly left the fac­tory with. Rac­ing bikes usu­ally left the works with close ra­tio BAPC boxes – even Vin­cent fac­tory TT en­tries had their spe­cial BAR boxes re­moved and re­placed with th­ese when sold on – un­less a buyer ac­tu­ally spec­i­fied BAPH road ra­tios. So PUB is on the lookout for a set of close ra­tio in­ter­nals to build up the sec­ond box with. Un­like the stan­dard in­ter­nals, which are mostly much the same as or­di­nary Ariels (and Pan­thers), the close ra­tio gears are very dif­fer­ent.

In the early thir­ties, Bur­man ap­pear to have beefed up their boxes by ba­si­cally mak­ing the gears wider, al­though tooth forms did change a lit­tle. Even­tu­ally, this got very crowded in­side, which they got around by re­plac­ing the old face-dogs and cut­ting in­ter­nal ‘gear teeth’ into the pin­ions to work as dogs when the ap­pro­pri­ate pin­ions tele­scoped to­gether. PUB sur­mises that this only worked when

the var­i­ous gears had sig­nif­i­cantly dif­fer­ent num­bers of teeth, and there­fore di­am­e­ters. The close ra­tio gears per­haps did not per­mit this, in any case they re­mained of the older pat­tern with face dogs (as used late-20s, early 30s stan­dard boxes) – whose coarse­ness also made for quicker rac­ing changes. So PUB has been on the lookout for th­ese. In fact she has amassed a few parts, and been promised some more. Un­for­tu­nately she cur­rently only has six out of eight gears, but worse still th­ese are a mix of close and stan­dard ra­tios that do not make a set! Boo. Even more awk­wardly, she has dis­cov­ered that when own­ers have com­mis­sioned new gears to re­place old, worn, ones, they have not repli­cated the ‘slid­ing dog’, but re-used their old ones. This slid­ing dog is dif­fer­ent to the later BAP item (face dogs in­stead of gear-tooth type) and is now very rare. PUB spot­ted some parts on eBay, in­clud­ing such a dog, and snapped them up. She now has a lot of gears, many of which she can­not even iden­tify, and one slid­ing dog … from a smaller pat­tern of Bur­man box. Boo, and boo again. So PUB is now be­com­ing an ex­pert on the BA and BAP boxes, the ‘P’ by the way stand­ing for ‘piv­otal’ which re­flects the mount­ing and ad­just­ment (by piv­ot­ing the gear­box on one of its studs). This re­placed the older 2 and 4 stud top (or some­times bot­tom) vin­tage type mount­ings. Bur­man lit­er­a­ture lists three ba­sic sets of gear ra­tios as fol­lows, and con­tin­ued their vin­tage prac­tice of re­fer­ring to gear sets as H and L (for high and low).

The stan­dard and wide ra­tio sets dif­fer only in their sleeve (out­put) gears and the mat­ing layshaft gears, and th­ese were the ra­tios main­tained through to post-war years. The close ra­tio set uses a third size of those pin­ions, and also changed most of the oth­ers, but as men­tioned above was not con­verted from the early face dog nar­row gears to the gear-tooth dogs and wider gears. The lack of rac­ing gearsets is the rea­son why Vin­cent had to change to Al­bion gear­boxes for their Grey Flash models post-war.

When the old type nar­row gears can be found, it is pos­si­ble to mix and match be­tween the stan­dard and close ra­tio pin­ion pairs. Us­ing the stan­dard 3rd gear pin­ions in a close ra­tio clus­ter raises third gear even closer to top (1.08:1), whilst us­ing the stan­dard 1st gear pin­ions (which in­cludes the dou­ble gear) low­ers first (to 2.3:1) and is prob­a­bly a good idea for a racer-on-the-road. The stan­dard ra­tios could also be jug­gled a bit in the same way. Bur­man lit­er­a­ture does make ref­er­ence to per­haps four dif­fer­ent ‘close ra­tio’ clus­ters, but they may have just been th­ese al­ter­na­tive per­mu­ta­tions of the same few gears. One good re­sult of this is that if PUB keeps col­lect­ing any of th­ese pin­ions she can find it greatly in­creases her chance of be­ing able to make up one of the per­mu­ta­tions. The only prob­lem is that the CR 31 tooth sleeve gear is nec­es­sary, and what she has got is the 33 tooth! Oh well, keep look­ing.

Read­ers with longer mem­o­ries may re­mem­ber that PUB’s sidevalve HRD had a gear­box dis­as­ter some years ago, with a bro­ken low gear pin­ion (22 tooth). She has been look­ing for an­other one (or bet­ter still a 19 tooth and 33 tooth wider ra­tio pair), and turned up noth­ing in the mean­time. If any­one knows the where­abouts of a Bur­man gear mine PUB would dearly like to know its where­abouts!

She did say that it was Bur­man anorak time this month, or per­haps time to take up stamp col­lect­ing again.

Now, just for some­thing a lit­tle dif­fer­ent to fin­ish on, an old univer­sity friend re­cently sent a photo of their fa­ther in a wartime side­car out­fit, which he thought might be Amer­i­can. The bike is barely vis­i­ble, al­though the fork looks like an English girder, and the side­car is on the left. But that side­car is very dis­tinc­tive, and is the side­car wheel drive job fit­ted to WD Big Four Nor­tons. It was also men­tioned that the rider and pas­sen­ger had had a cou­ple of ac­ci­dents – which might just have been down to the trick­i­ness of side­car out­fits in gen­eral, but may also have been down to that side­car wheel drive. If the rider failed to dis­en­gage it on re­turn­ing to a hard sur­face, such as tar­mac, the ma­chine could prove al­most un-steer­able due to the lack of any dif­fer­en­tial. When the Big Four out­fits were re­leased onto the civil­ian mar­ket postWWII the min­istry had the shafts cut and re­moved for safety, and it may have been a wise move.

Left: BAP gear­box near­ing com­ple­tion, with the gears and in­ner case as­sem­bled, but with the outer case and pos­i­tive stop mech­a­nism still to be at­tended to. Whether this was just be­fore suc­cess­ful com­ple­tion, or ear­lier when the outer case had to be...

Below: This sleeve gear is a 33t stan­dard part, and for a close ra­tio box it needs to be 31t – no al­ter­na­tives ac­cept­able

The early pat­tern BA and BAP boxes used nar­rower teeth and coarse pat­tern face dogs as seen here. Ap­par­ently the close ra­tio boxes only used this type, but, un­for­tu­nately, not only are there only 6 out of 8 pin­ions in this clus­ter, but the ‘pairs’ are...

Above: When the ‘Beast from the East’ struck, it was too cold for work in un­heated garage or shed Above: A spare Bur­man BAP gear clus­ter. This is a stan­dard, road-go­ing, set of ra­tios fea­tur­ing wide gear­wheels. Note the ‘slid­ing dog’ in the cen­tre of...

The gear clus­ter, and a ta­ble of the pin­ions, of a Bur­man ‘BAP’ gear­box, as used on Ariels, Vin­cent 500s, Pan­thers, etc. The CP box used by AJS / Match­less is very sim­i­lar in con­struc­tion, but uses dif­fer­ent pin­ions so the ta­ble does not ap­ply to them

The CR gearset needs one of this type of ‘slid­ing dog’, but un­for­tu­nately this one is from a lighter weight gear­box. It is about 35mm di­am­e­ter, whereas the right one is about 45mm. An­other boo then A friend found this photo of his fa­ther in the 40s....

Newspapers in English

Newspapers from UK

© PressReader. All rights reserved.