Author Topic: Geabox casing mismatch s/a  (Read 500 times)

Offline Jules

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Geabox casing mismatch s/a
« 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????

Online JulianS

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Re: Geabox casing mismatch s/a
« Reply #1 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.

Offline Jules

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Re: Geabox casing mismatch s/a
« Reply #2 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*

Online berger

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Re: Geabox casing mismatch s/a
« Reply #3 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

Online RDfella

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Re: Geabox casing mismatch s/a
« Reply #4 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.
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Offline Jules

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Re: Geabox casing mismatch s/a
« Reply #5 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?)..

Online berger

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Re: Geabox casing mismatch s/a
« Reply #6 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.

Online RDfella

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Re: Geabox casing mismatch s/a
« Reply #7 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.
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Offline Jules

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Re: Geabox casing mismatch s/a
« Reply #8 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

Offline Swarfcut

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Re: Geabox casing mismatch s/a
« Reply #9 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.

Swarfy

Online muskrat

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Re: Geabox casing mismatch s/a
« Reply #10 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.
Cheers
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Offline Jules

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Re: Geabox casing mismatch s/a
« Reply #11 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*

Offline Jules

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Re: Geabox casing mismatch s/a
« Reply #12 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

Online berger

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Re: Geabox casing mismatch s/a
« Reply #13 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

Offline Swarfcut

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Re: Geabox casing mismatch s/a
« Reply #14 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.

 Swarfy

*Translation of bergerspeak.