Gearbox build from scratch

[Jules]

Hi all, the coronavirus lockdown here in Australia has prompted a look at some things to be done at home and one of those is to start my gearbox build. My '56 s/a A10 gearbox has been in bits for donkies years now so maybe a good opportunity to get the bits out and start the build - is there anywhere on the forum that I can pull down a "this is how you build an A10 gearbox" document(s)?? I guess I'm particularly interested in where to start, what to look out for regarding tolerances and fits, which things to do in what order, as well of course where everything goes ????? Perhaps a tall order, but everything helps at this point in time  cheers

[Swarfcut]

Well, here's my take on it.

  Parts books or Draganfly online parts  diagrams etc identify what you should have, so before spending money, see what you have noting what goes where.

   While you wait for other Forum members to add their hard won experiences, study "Home Gynaecology For Beginners" The techniques therin are certainly a requisite for reassembly, along with a third or fourth hand. To paraphrase Haynes once more. " Reassembly is the reversal....."      But we all know this publication is prone to error.

 So, try putting it back together. That way you practice what to do and bits don't get lost while you ponder your way forward. Usual problems are with worn shafts, bearings and bushes, particularly the blind layshaft bush which has a hard life on standard boxes. Worn and pitted gears, although not the epitome of perfection, are well worth trying rather than discarding outright. We don't spend much time in the lower gears, do we?

Plenty of stuff on the Forum about gearboxes, problems and fixes.

 Swarfy.



 

[RichardL]

Though frequently disrespected for various reasons, the Haynes manual guided me through my one gearbox rebuild back around 2005. I had no previous experience with any gearbox rebuild and it has worked well for about 9,000 miles.

The reference to trying to birth a stubborn baby is not far off.

Richard L.

[KiwiGF]

Hi all, the coronavirus lockdown here in Australia has prompted a look at some things to be done at home and one of those is to start my gearbox build. My '56 s/a A10 gearbox has been in bits for donkies years now so maybe a good opportunity to get the bits out and start the build - is there anywhere on the forum that I can pull down a "this is how you build an A10 gearbox" document(s)?? I guess I'm particularly interested in where to start, what to look out for regarding tolerances and fits, which things to do in what order, as well of course where everything goes ????? Perhaps a tall order, but everything helps at this point in time  cheers

I’ve rebuilt a few bsa gearbox’s now (the b31 rigid box just last weekend after 3rd stopped working). Compared to an engine it’s simple, but many people don’t want to even try   

However, if you just look at the inner compartment where the “complicated” gears are and which puts people off, it’s just two shafts both with 4 gears on, one shaft with two selector forks on, a camplate and one or two spacers....the 4 gear pairs all total the same number of teeth (43? From memory).

Replacing layshaft bushes usually requires machining but the mainshaft ball races are easily replaced.

Getting layshaft end float in tolerance can take a bit of messing about, but again is not too tricky.

One “gotcha” is the kickstart mechanism, there is thin wall bronze bush inside the gear that you can mess up by over tightening the mainshaft nut.

Good luck! (But you shouldn’t need it)

[scotty]

I’ve done both my A & B boxes with the help of Haynes and this old article from
a book on pre unit twins
Hope the quality of the pics is readable if you zoom in.

[Jules]

Hi Scotty, thanks for the pics, I couldn't quite read the text but I "googled" the article and found it has been uploaded via this link - its exactly the same but clearer as a .pdf....thanks so much, it seems quite straightforward (we'll see!)
http://www.tracyrball.com/files/Triumph%20Tigress%20Files/Rebuild%20A%20Beeza%20Box.pdf
I remember reading Motorcycle Mechanics back then too, they always had good articles about BSAs and Triumphs etc, enjoyed reading them and trying out some of the ideas. I remember reading about tuning up A10's for example back then and a friend did just that and created an unbeatable (for us mates) bike. If anybody has that old article I'd like to re read it now and see if it still makes sense!
Just reading through the other prompts is good, reinforces the "ain't really hard" principle(!) thanks all. One thing that did strike me as not so easy is the blind (layshaft?) bush, it seems quite worn compared to the others in the box, but replacing it and getting it "right" may be difficult, if I leave it alone will it be troublesome or just a bit noisey (I don't know if everything worked before or not)?
Also, the clutch lever wobbles about in its bush, I think that will need fixing, I seem to remember reading a few fixes for this, is there something that can be done simply at home ie doesn't require expensive machining (last time I tried getting some machining done it was very expensive and I had to keep chasing it, machine shops give this sort of thing very low priority, but high cost), thanks, all ideas welcome, it looks like I'll have plenty of time on my hands currently! cheers

[Slymo]

Really pretty straight forward. I've litterally put mine back in the bike yesterday. There are two ball races that can be obtained (lockdown aside) from your local bearing supply merchant and three bronze bushes. One blind one for the drive side of the layshaft one open one at the inner cover side of the layshaft and one double one in the sleeve gear. The only trap for young players that I came across was putting the spacer that goes on the mainshaft cover end inside the cover rather than outside under the kickstart cog (whoops another floating bronze bush in there). The bronze bushes are by far the most invloved to fit so check that they actually need replacing. Up and down wiggle on the input shaft says the sleeve gear bush is kaput but if thats good and there isn't any noticable play in the others I'd just replace the ball races and suck it and see.

[KiwiGF]

Hi Scotty, thanks for the pics, I couldn't quite read the text but I "googled" the article and found it has been uploaded via this link - its exactly the same but clearer as a .pdf....thanks so much, it seems quite straightforward (we'll see!)
http://www.tracyrball.com/files/Triumph%20Tigress%20Files/Rebuild%20A%20Beeza%20Box.pdf
I remember reading Motorcycle Mechanics back then too, they always had good articles about BSAs and Triumphs etc, enjoyed reading them and trying out some of the ideas. I remember reading about tuning up A10's for example back then and a friend did just that and created an unbeatable (for us mates) bike. If anybody has that old article I'd like to re read it now and see if it still makes sense!
Just reading through the other prompts is good, reinforces the "ain't really hard" principle(!) thanks all. One thing that did strike me as not so easy is the blind (layshaft?) bush, it seems quite worn compared to the others in the box, but replacing it and getting it "right" may be difficult, if I leave it alone will it be troublesome or just a bit noisey (I don't know if everything worked before or not)?
Also, the clutch lever wobbles about in its bush, I think that will need fixing, I seem to remember reading a few fixes for this, is there something that can be done simply at home ie doesn't require expensive machining (last time I tried getting some machining done it was very expensive and I had to keep chasing it, machine shops give this sort of thing very low priority, but high cost), thanks, all ideas welcome, it looks like I'll have plenty of time on my hands currently! cheers

The blind layshaft bush would be a challenge to replace without a good machinest, first thing is to measure the layshaft, if it’s oval or undersize you will need to buy an undersize Bush, from memory  012” is available.

You can then get the layshaft ground to suit the (installed) bush, or just clean up the layshaft to get it round, and get the (installed) bush machined to suit it. I say installed as it will slightly reduce in dia when fitted in the case.

I managed to “machine” sleeve gear bushes to size by using a cheap brake cylinder hone, if enough clearance is not allowed, they seize! (Oil has to be able to get inside the bushes).

[JulianS]

Carefully check the mainshaft fixed "G" gear - wear and rounding to the ends of the teeth where they engage with the sliding "E" gear can cause slipping out of third gear especially when accelerating.

Photo bottom shaft gear is worn, top shaft gear is good condition.

[JulianS]

The factory service sheets are quite useful.

311 below.

[Jules]

thanks Julian and all, great prompts, partic. the wear pics, I'll be sure to look at that much closer....whats the thinking wrt the clutch lever bushing, any ideas for that? cheers

[Swarfcut]

Jules .. Just looking at service sheet 311 Dismantling. It appears the mainshaft, kickstart assembly and inner cover can be removed as a complete sub assembly. While this is probably true with a good bit of manipulation, I would consider this lump to well nigh impossible to replace as is without a great deal of frustration.

 It is easier to remove the mainshaft nut, kickstart ratchet etc and tap the mainshaft gently through the bearing as the inner cover is withdrawn. This leaves all the gears and shafts in place to be excavated, once the selector rod has been removed the whole of the internals has more freedom to aid removal.

  This could be the source of the reputation that rebuilding the box was difficult.

  Reassembly. A few things to consider....Layshaft endfloat is controlled by a hardened steel thrust washer between the big bottom gear layshaft cog, and the end of the layshaft. Inner edge is champhered, which goes towards the clutch side to clear the change of diameter of the layshaft at this point, which has a slight radius to the  profile here.

   Check selector rod for bends and bows, make sure camplate does not bear too tightly against the selector arms, Check by assembling just inner cover, selector arms and rod against the camplate. Typically problem with a NOS camplate which was a factory reject because it was too thick.

  Load the shell with the shafts, gears and selector arms, then refit the selector rod but leave out the retaining grubscrew. Fit the inner cover, moving the rod sideways if required to get it into its hole.  Many gearbox shells have had the casing damaged by driving the cover down onto the mis -aligned rod,  supported by the grubscrew which simply took a chunk from the case.

 It really is quite simple, and with your new found skill (which was appreciated by at least one member who understood my drift)

 As standard that pesky clutch lever runs directly in the outer cover. Remedy is substitution of parts/ worn part, build up if wear on lever shaft, custom bush to fit cleaned up shaft and cover.. In the old days finding a better assembly was the easy, long gone option.


 Cheers.

 Swarfy.

  Additional. As of today serious restrictions have been placed on the UK population. We are all required to stay at home and limit our social contacts. No problem, it's my normal lifestyle. I stick with folks I like.

[JulianS]

Easier to remove the mainshaft/ks assembly whilst still attached to the inner cover - the nut needs to be very tight and often the shaft is quite tight in the bearing.

On reassembly the mainshaft assembled on the inner cover can be gripped in soft vice jaws and the ks nut firmly tightened.

With sleeve gear in place assemble the layshaft, less H gear in the box with the lower selector . assemble to 2 middle mainshaft gears with upper selector then feed selector shaft through and into the case.

The mainshaft is then threaded through the middle gears, slightly rotating as necessary, and aligning the quadrant/inner cover marks. This also avoids tapping the cover over the shaft and having to lock the sprocket to tighten the nut.

Works for me every time.

[Swarfcut]

Julian. Thanks for a different aspect of assembly. I can see who did the course and passed with distinction...and it wasn't me. I struggled to line up the gears as the inner cover closed down, hence my cheat's method.
 
 There you are folks, two different approaches to the same problem, so use whichever works for you.

 Swarfy.

[chaterlea25]

Hi All

the nut needs to be very tight and often the shaft is quite tight in the bearing.

I will have to disagree with the above statement somewhat
Over tightening the nut will compress the bronze bush and lock the ratchet mechanism
I would go with firm tightening

John