PUBtalk ...................................................... 102
PUB is in anorak mode over BAPs. Not that sort, but Burman BAP gearboxes…
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....