The BSA A7-A10 Forum

Technical => Clutch, Primary, Gearbox => Topic started by: Jules on 09.05. 2021 08:36

Title: Geabox casing mismatch s/a
Post by: Jules on 09.05. 2021 08:36
I'm just polishing up my replacement outer gearbox case before assembling, and noticed that the casting boss for the clutch lever is sitting up higher than the casing top - my old (broken) cover sits almost flush. Ha I thought, thats good, a longer boss means better control of the clutch operating rod, wrong, I just measured the boss lengths and they are the same!
The replacement casing is displaced by a few mm downwards, all the screw holes and dowels line up and the two parts fit perfectly together but with this unsightly mismatch.
Anybody come across this before, they are same part nos. and everything looks the same, so I assume its just a different die with an offset ?? I'm a bit anxious now whether there is anything else I need to check before trying to assemble everything together, I'm assuming that the machining/alignment would all match because they would machine it all at once using the same master m/c points, wouldn't they????
Title: Re: Geabox casing mismatch s/a
Post by: JulianS on 09.05. 2021 09:30
Your old case has had a bush fitted, the originals had no bush but sometimes one fitted to rectify wear.

With a change of outer you need to check that the kickstart  and gearchange bushes align and that the speedo drive gears mesh properly.
Title: Re: Geabox casing mismatch s/a
Post by: Jules on 09.05. 2021 11:08
thanks Julian, I guess thats what I was thinking maybe an issue (but hoping not!). Is this type of casting offset "usual" I reckon there's maybe 4 mm step between the (new) outer and the inner case, maybe 1mm on the original....
As far as checking the kickstart and gearchange bush alignment is concerned, is that just a matter of they assemble and work or they dont? The speedometer drive I wont really know until its on the road, unless it jams on assy of course.... I'm hoping that all the holes/boring would have been m/c originally using the same ref. points, regardless of the casting offset  *doubt*
Title: Re: Geabox casing mismatch s/a
Post by: berger on 09.05. 2021 12:04
i have come across these miss matches with some of the ones i have and was more worried about gasket face sealing. having said that i used cases with a similar miss match to yours and it went together ok
Title: Re: Geabox casing mismatch s/a
Post by: RDfella on 09.05. 2021 16:04
The line doesn't quite 'flow'. Maybe it's had a hit at some time? Are the cases the same thickness at this point? Or maybe the linishing guy at the factory got a bit carried away ......  Anyway, best check the face is flat on a known good flat surface.
Title: Re: Geabox casing mismatch s/a
Post by: Jules on 10.05. 2021 01:38
Berger, your experience was just what I was hoping to hear, and I agree with the concern about sealing face/joint integrity too, I guess thats something I'll need to pay attention to for final assy., thanks  *smile*
RD, the case is sound and in good condition, the issue really is just one of offset - if you look at the last pic you can see the amount of metal around the (top) screw hole bosses is quite small, such that the cheese head screw may well "stick out" (unless I use allen heads?)..
Title: Re: Geabox casing mismatch s/a
Post by: berger on 10.05. 2021 09:18
jules, the top screw hole bosses in the last pic? do you mean the holes that the studs go through and have washers and nuts on, if so just put a flat on the washers. use thick washers also.
Title: Re: Geabox casing mismatch s/a
Post by: RDfella on 10.05. 2021 12:27
Jules, if indeed it is an offset issue, best check the kickstart bush and gearchange line up OK. Given the old equipment and practises british manufacturers were using in those days, I doubt the mounting holes / counterbores were done on the same station as the kickstart / gearchange. Maybe not even on the same jig.
Title: Re: Geabox casing mismatch s/a
Post by: Jules on 11.05. 2021 12:19
yep, you are right Berger, I meant the stud holes and yep as long as its "just" that issue and the sealing faces are ok, then a flat side on the washer will suffice, I agree...I am feeling more comfortable now too after your experience, BUT I will check out the gearbox and kickstart alignment between these 2 cases first per RD and Julians comments. Fingers crossed they are ok because if not I cant see how to fix that (readily)!! cheers
Title: Re: Geabox casing mismatch s/a
Post by: Swarfcut on 11.05. 2021 12:47
  I've also come across this problem more with perfectly matching covers and inners fitting together just fine, then a big step to the main case. The holes all line up, but cosmetically and from a gasket face match not so good. The assumption is that the die castings remained  exactly the same from beginning to end. Is this actually possible? In other words  a good chance that castings from a particular period will all match, a mix from different era's may show variations. Add to that variations in the linishing process and the no doubt subjective quality control of the time.

  If truth be known this whole factory operation could  have included a so called selective assembly step for those castings otherwise condemned as off spec.   Bad luck if that used part is the only one to hand, another one has an equal chance of perfection or being even worse.

Title: Re: Geabox casing mismatch s/a
Post by: muskrat on 11.05. 2021 21:22
G'day Fellas.
I once worked in a factory making elevators. My job on the horizontal borer was machining gearbox's and brake systems from raw castings.
Some castings were anything from 1 to 5 mm higher/wider/longer than the last one. They all got set on the same point so some needed more machining than others. So in the end we'd have this situation being discussed. All the shafts would be in the right relationship to one another and work fine but some of the covers would overhang the case.
Jules, if the shafts fit and turn I wouldn't be too fussed on the miss match of the covers.
Title: Re: Geabox casing mismatch s/a
Post by: Jules on 13.05. 2021 11:38
Hi Musky, yep I thought that the machine reference points would have to be the same based on the dowels to locate the covers, but it has been reassuring to hear people's actual experiences. I tried the kick start and g'box shafts today and they seem to line up ok, which is a relief, not sure why the cover didn't sit down fully together yet though, more investigation req'd on that....the offset does look ugly though  *sad2*
Title: Re: Geabox casing mismatch s/a
Post by: Jules on 22.05. 2021 11:42
Hi all, well I've had a further look at the two cases not joining together and its nothing to do with the new case, even the old case wont assemble together, with the kickstart shaft/quadrant installed, weird! It was all assembled before I tore it down, it was never a runner though when I got the bike, so whether it did actually work I dont know. I do know that the case did not "spring apart" when I undid the nuts, so do not believe it was under tension then, but I cannot see how that could possibly have been the case. Its all the same parts going together, yet its impossible to join the cases, the kickstart shaft holds them about 2-3 mm apart!
In the pics you can see a small clearance between the inner case and the kick shaft with the quadrant actually sitting on the stop shoulder, but thats only about 1mm maybe, but the quadrant needs to be at least 1/2 mm off the stop shoulder too, but there's no clearance to the outer casing bush face already????
So it seems to me that the inside distance between the two kick shaft bushes is too small by around 3mm, how on earth can that happen when nothing has been touched??????????am I missing something here???? all ideas welcome, cheers
Title: Re: Geabox casing mismatch s/a
Post by: berger on 22.05. 2021 16:36
have you turned the kicker shaft when fitting the case, you need to turn it for it to engage than the case will go on
Title: Re: Geabox casing mismatch s/a
Post by: Swarfcut on 22.05. 2021 18:08
 The inner cover kickstart shaft bush has a top hat face to bear against the quadrant. The outer cover bush is a plain steel sleeve, inner edge is flush with the outer cover casting boss. A  gearbox here selected at random has a plain shank to the quadrant stop, the one pictured has a shoulder, so some element of difference there. That shoulder looks to be preventing the quadrant reaching the bush face in that position. Easy to check if this is the problem. If it all fits with the stop removed, time for a think.

  Quadrants and pinions come as flat topped or pointy teeth.  Make sure you have matching pair, both the same, not a mix. On assembly the kickstart  shaft has to be rotated against the return spring enough  for the quadrant to clear the stop.* This will allow the quadrant to settle against the top hat bush in the inner cover as the outer slides into place.


*Translation of bergerspeak.
Title: Re: Geabox casing mismatch s/a
Post by: muskrat on 22.05. 2021 20:49
G'day Jules.
I agree with Swarfy as to the stop pin. Should be a straight pin, no top hat.
Also the bare spline should have a shrink on sleeve to stop the quad walking on the shaft. The repros are one piece (shaft & quad).
Title: Re: Geabox casing mismatch s/a
Post by: chaterlea25 on 23.05. 2021 00:11
Hi All,
It looks from the photos that the quadrant is not pressed fully onto the shaft?
It's also the other end of the quadrant  that meets the stop, the spring end is shown?
I don't know if that makes a difference?
I put up a post a long time ago showing a flanged stop pin as part of a repair process
for damaged cases, i have done quite a number of them and have not had an issue
Maybe whoever did this one made the flange a little thicker??

Title: Re: Geabox casing mismatch s/a
Post by: Jules on 23.05. 2021 08:14
thanks for the feedback and focus on the kickshaft, I can understand why that is, having read your notes, so let me try and summarise:
* the first thing is, that all these bits were already assembled when I got the bike (engine was blown up, so no go, plus miriad other issues with the frame etc!), but the bike was "whole" and theoretically driveable "just" with a blown up engine, so presumably it went together ok before, so why not now???
* assuming it wasn't assembled properly before (somehow??) then I clearly have to change something to make this go together and it seems that the quadrant is out of position to start with. It looks to have been pressed onto the "spline", but not far enough? should the quadrant align with the bottom of the shaft or just press all the way up to the shoulder/stop on the shaft? Looking at Musky's pic, it seems that it shouldn't go all the way up and there should be a "spacer" (?) there, so how do I get this quadrant positioned correctly please?
* AND Musky, the quadrant looks like its awfully tight on the "spline" when its been pressed into position, I cant see how another spacer behind it sitting over the splines would really make any difference to its holding location, thoughts?
* now the shouldered stop, John's comment seems to suggest that the gearbox has been repaired at some stage and I believe thats the case, the bushes are clearly not original through the box, and seem to still be in reasonable condition. I think the shouldered stop is probably a good thing wrt its function too per John's past idea, so if I (can!) push the quadrant further on such that it aligns with the bottom of the spline, it will clear the shoulder, but will that misalign the pinion?? (I'm not in a position to fully assemble the box yet, so can't check that, what are your thoughts on this alignment please?)
* Finally, Swarfy's ideas about shaft location between the 2 steel bushes makes perfect sense, I have a top hat bush in the inner case and a plain sleeve in the outer, the outer sleeves for both the gearshift shaft and the kicker shaft are "almost" aligned to the bosses in the case maybe just a slight protrusion (to take the thrust away from the aluminium boss?), are they correctely located? If I (can!) move the quadrant on the shaft further up so that the quadrant and bottom of the spline align, then I suspect it will need end float adjustment/shimming....
Soooooooo, whats your thinking with all this please? thanks for your help as's couple pics of the quadrant/shaft
Title: Re: Geabox casing mismatch s/a
Post by: Swarfcut on 23.05. 2021 09:18
 Jules. That last picture is worth 1000 words, the quadrant is the problem.  The face of the quadrant and end of the splines should be level to give the most area of contact against the top hat of the inner cover bush. You should then find the outer cover fits and with the gasket in place the kickstart shaft has a small amount of end float and turns easily. The collar on the stop pin is of no consequence providing it is clear of the quadrant and does not obstruct it. If the bush in the outer cover needs repositioning, heat up the cover before applying any force to the bush.

  Early gearboxes have a flat return spring. This engages on the exposed shaft splines, a relatively poor set up. Later design is for a conventional coil spring, hooked over the quadrant.  The spacer mentioned  (Part 67 3173 Spindle Sleeve) fits on the shaft over the splines and helps to support the coils of the spring.  This is shown in place in Musky's picture. Obviously not used with  the earlier flat spring variants. Later quadrants have this spacer incorporated into the design as a one piece unit, but  fortunately for the coil spring design  of box they are all mix'n match. Early quadrants can be used with late boxes as long as a matching tooth type pinion is used. You can see that in this case the exposed splines serve no purpose and are a leftover from the early  flat spring design, adapted with the use of the sleeve to suit a later application at minimum cost. Later variants  of quadrant are a brazed up one piece part.

  Moving the quadrant on the shaft splines should require a fair amount of force.  If it's a sliding fit that could also answer why it all fitted to start with.  A press would be handy, a big vice may do it. Don't go smacking the shaft, that's the hooligan's way.

 The mystery of how it all went together remains. Tell us what you find.

 In use, never let the kickstart pedal return with a bang. That is how the stop and its location suffer, comes loose and frets the mounting hole in the inner cover.

Title: Re: Geabox casing mismatch s/a
Post by: Jules on 24.05. 2021 00:53
thanks Swarfy, to confirm, I need to have the quadrant aligned "just" to the end of the splines, NOT pushed all the way up to the top of the splines and, I guess that "spacer" is needed to support the spring, I dont remember seeing that on teardown either, particularly as Musky mentioned its pressed into place too....
I still cannot understand how it was ever assembled before  *dunno* *cry*, cheers
Title: Re: Geabox casing mismatch s/a
Post by: Swarfcut on 24.05. 2021 07:17
 Jules. Just to the end of the splines is right. In practice such a feat of precision may be difficult to achieve, Quadrant much above the splines.... too big to fit, as now. Quadrant below....should fit fine, but only the splines bear against the top hat. Dead level, best of both worlds. Then of course consider any end float and sod all that and position the quadrant to give the best free rotation with no appreciable axial movement. It will all depend on what you actually have regarding manufacturing tolerances, wear, castings, bush thickness, gasket thickness etc.

  A similar situation can be seen with the position of the layshaft fixed pinion on the layshaft. Here the design uses a circlip to act as a stop when the pinion is pressed onto the layshaft.  Pinion ends up marginally proud of the splines and takes the thrust against the blind bush. So here, above the splines slightly, no float, should be fine if that's how it ends up.

 Out of interest, your quadrant has so called pointy teeth. For comparision Musky's shows what looks like the  flat topped version.

Title: Re: Geabox casing mismatch s/a
Post by: Jules on 24.05. 2021 08:13
Hi Swarfy, thanks for the follow through, appreciated....I did a thread on my quadrant and the new pinion that was sent to me from C&S(?)earlier and you guys did a great job then explaining pointy teeth vs flat teeth and also identified that the new pinion wasn't right either!! so from that I decided to reuse what I have which is still serviceable abeit not as good as I wanted for full rebuild.
Which leads nicely into what I have done today on the assy issue.....
I found the spacer that Musky identified in his pic, but its a sliding fit not press on Musky??
I managed to press the quadrant on until it bottomed on the spline shoulder Swarfy, which gave a perfect alignment to the bottom face of the shaft bearing  *smile*, it actually moved relatively easily, which surprised me.
The quadrant still contacted the flange on the quadrant stop though because the stop flange was 3mm while the flange on the top hat bush was only 2.5mm. The flange on the stop I m/c 'ed down to 2mm and all clear, aaaaaaannnnnnnnnndddddddddd the casings fit together  *smile*, just the bearings and endfloat to sort now, thanks all  *beer*
PS I still have absolutely no idea how it could possibly have gone together before!! but then my memory is not as good as it used to be and I did tear this down years ago lol  *conf*
Title: Re: Geabox casing mismatch s/a
Post by: Jules on 26.05. 2021 13:24
PS just to close out this thread and info. for others who have to get another case like I did....I think this case must have been in the rejected pile and then used up later in life, because apart from the joint face mismatch I also found the gear selector shaft fouled on an internal boss! The boss that the selector shaft fork straddles had a greater draft angle on it such that at the bottom closest to the case outer, the fork fouled as the shaft rotated...anyway, here's some pics to close out, I'm hoping that the sealing surfaces will be sufficient to seal up on final assy. you can see the reduced seal from the texta line...thanks for your guidance on all this too  *good3*