The BSA A7-A10 Forum

Technical => Clutch, Primary, Gearbox => Topic started by: Rich on 14.03. 2019 19:53

Title: problem with assembling a gearbox
Post by: Rich on 14.03. 2019 19:53
I was asked by a friend to refurbish his gearbox, now this is one he bought 11 years ago with a basket case bike, it was a bit corroded, I took it apart and inspected it, the gears had pitting on some of the teeth, the layshaft was worn both ends and needed grinding, all the bushes were worn as were the roller bearings, so he decided to take a chance and buy another one from EBay, this box was in better condition, so new bushes throughout and new roller bearings and it is all back together and working fine, except for a noisy 2 and 3rd gear which I cannot do much about unless he splashes out on a new gear cluster. However I decided to put the old gearbox back together, but was unable to get the inner cover on as the shafts would not line up, upon inspection the second gear was not meshing so first gear was unable to mesh as well, my first thought was that I had it assembled incorrectly, but you cant really get the gears in the wrong place, so Had I mixed up a gear from the old box, I had kept them apart so unlikely,  so I stripped the refurbished box and checked it, all was correct, in fact the 4th and 3rd gear had a different number of teeth and the  first gear and 2nd gear on the layshaft had a different mesh design, the teeth profile look the same, so what next?
Title: Re: problem with assembling a gearbox
Post by: morris on 14.03. 2019 20:35
I'd say that if the shafts don't line up the gears are wrong?
Maybe the gear chart in this thread/post might help ?
Title: Re: problem with assembling a gearbox
Post by: Swarfcut on 14.03. 2019 22:47
Hi Rich..    As this is a BSA A10 Forum, is your box a standard  Plunger or Swing Arm box, or as you mention roller bearings, a more exotic variant (or even an A65)?   Standard A7/10 boxes have plain bushes on the layshaft and  simple ball races on the mainshaft and sleeve gear.

 First step is to make sure you actually have the correct mainshaft and layshaft for the box, as there are subtle differences in application and year. Same with the actual gears. The number of teeth  can vary, depending on the type of box and whether it is standard, close ratio or even scrambler. The gears also vary with regard to adjacent drive dog design, again depending on year.  The plunger box shares some gears with the S/A box, depending on year. So there is plenty of scope for mis-matched parts.

     There is plenty of information on the Forum, start by following the link above posted by morris.

     For a more detailed overview, try  Draganfly,  who have a good website with exploded diagrams and part numbers to aid identification of what you have.

 Chances are that as a basket case box, some of the gears look OK, but are in fact completely wrong.  Start trial assembly with just the shafts, then add pairs of gears, checking as you go that the inner cover fits. Leave out the camplate and gear selector forks for the time being, sort out the basics first.

Title: Re: problem with assembling a gearbox
Post by: chaterlea25 on 14.03. 2019 23:35
Hi Rich,
If you add the tooth count for each pair of gears together you should get the magic number 43
If they don't add up then a wrong gear is in there
There are also different width gears that look almost right and different engagement dog types to add to the confusion
 *pull hair out*
Title: Re: problem with assembling a gearbox
Post by: muskrat on 15.03. 2019 07:49
G'day Rich.
The question has to be asked. What breed of box is it? Forest Gump "Life is like a box of chocolates".
Title: Re: problem with assembling a gearbox
Post by: Rich on 15.03. 2019 08:19
Hi all, thanks for the replies, it is an A10 swinging arm box, in fact they both are, I was told that if there was no thread in the clutch cable hole on the gearbox cover, then they were both late boxes, both are.What I cant understand is that I took it apart, puts the bits in a container and am positive I have not mixed the two together, in fact as I said, I stripped the completed gearbox down just to check, the gear drive digs are different between the two as are the 3rd and 4th gear tooth count, the completed box runs up )with a drill) ok and all gears work, be it that 2nd and 3rd are a bit on the noisy side, I made a note of the teeth number when I striped the completed box down after I came across my problem, the completed box has 43 teeth on each pair so is correct as a standard box, the old box is as follows mainshaft gear listed first, 4th--25+16  3rd--20+24 2nd--23+19  1st--17+27 so that is  from 4th 41, 44, 42, 44, all the teeth profiles look the same, I will check the link Morris to see what I have, but the mystery still remains as to why the gears will not let the shafts line up through the cases
Title: Re: problem with assembling a gearbox
Post by: Rich on 15.03. 2019 08:38
I have just looked at the gear chart and it looks as if it is a mismatch, with a couple of close ratio gears not matched to the others, how it was bolted together I do not know, I will recount them again, but have done this twice now, I think I will just have to scrap this box which is a shame as someone else could have refurbished it and I could have sold it on even in a poor condition and put the cash towards the Gold flash 4 spring clutch. will throw some outdoor clothes on and go into the workshop, but breakfast first, thanks all
Title: Re: problem with assembling a gearbox
Post by: Swarfcut on 15.03. 2019 08:58
Rich...   Do not simply scrap the box as all the parts have some value and will be useful to someone, somewhere who is looking for the bits you are going to dump.

 Standard ratios are...  Top Gear  26/17  3rd 20/23    2nd 24/19  Bottom Gear 16/27

 At first look only 3 of your gears  (20, 19, 27) are correct for a standard A series box. The 16 tooth layshaft pinion  looks to be misplaced, according to the chart on the above link, plus the 17 tooth mainshaft pinion as neither are listed on the chart in those positions.


Title: Re: problem with assembling a gearbox
Post by: Rich on 15.03. 2019 12:31
Had another go this morning after a nights sleep, now bear with me,
I swapped the 1st and second gear on the mainshaft with the fourth and third gear on the layshaft and all is resolved, the first gear mainshaft and the fourth gear layshaft are the ones that need drifting onto the shafts up to a circlip and I had fitted these to the wrong shafts, so now the magic number of 43 is correct for each pair of gears, the box is now assembled and ready to move on for someone who needs to refurbish a box, many thanks to you guys for your input.
Another question, when I bought the Gold Flash it came with some spares. namely a swinging arm gearbox with a straight mainshaft rather than the tapered one I have been working on, also a plunger box with the same sort of mainshaft, the bike itself is fitted with a 6 spring clutch, which I plan to replace later on with a 4 spring, why are the two swinging arm mainshaft's different?
Title: Re: problem with assembling a gearbox
Post by: Swarfcut on 15.03. 2019 12:59
Rich. Plunger boxes have a splined  mainshaft. The plunger clutch is completely different from any S/A clutch and is not interchangeable. The tapered shaft is for the S/A box, so looks as some previous owner has been playing at gearbox mix'n match.

Title: Re: problem with assembling a gearbox
Post by: JulianS on 15.03. 2019 13:41
The original swing arm mainshaft was tapered.

By changing to the plunger splined shaft a Norton clutch can be fitted.

Back in the 1960s Eddie Dow sold plunger shafts for this conversion.
Title: Re: problem with assembling a gearbox
Post by: Rich on 15.03. 2019 19:04
Thanks once more for your input, the gears are the standard gearbox configuration, I had counted one or two gears wrong so on paper they looked wrong, but this morning I started again and it is definitely a standard cluster.
Thanks JulianS I wonder if a Norton clutch will be better than the 4 spring one and cheaper to buy? I will have to do some research