Author Topic: Replacing bushes on gearbox mainshaft  (Read 622 times)

Offline chotus52

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Replacing bushes on gearbox mainshaft
« on: 05.02. 2018 02:35 »
Hi all,
On my 1955 Shooting Star, the bushing between the gearbox main shaft & sleeve pinion is worn excessively, allowing the whole clutch basket to move. If I’m correct, to change this I need to remove the gearbox outer case leaving kickstarter & gear lever in place, remove kickstarter ratchet pinion, remove inner gearbox cover & finally the mainshaft will slide out, leaving the lay shaft in place. Is this all correct? Do the two bushes on the main shaft just slide off? Thanks in advance for any advice. Regards
55 GF s/a

Online duTch

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Re: Replacing bushes on gearbox mainshaft
« Reply #1 on: 05.02. 2018 03:41 »
 yo're getting there, but after you've removed the outer case and inner 'sandwich/biscuit' case and clutch, then you need to remove the 1/4" grub screw behind the sprocket (it's vertically accessed from underneath with a smallish screwdiver) that retains the 'selector shaft', and then remove the selector shaft, the selector forks and associated gears...all 'em really....not hard but a bit fiddly...and then you need to remove the primary inner case and then the sprocket (if it's a swing arm model, otherwise if it's a Plunger model, and you haven't modified it like I did you'll need to remove the whole shebang, and split the engine/tranny to get at it  *eek*), so the sleeve gear can be removed, as the bushes are part of that...not hard, just fiddly

 I don't think I missed much...
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
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Offline chotus52

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Re: Replacing bushes on gearbox mainshaft
« Reply #2 on: 05.02. 2018 06:21 »
Tks DuTch.
It’s a 55 swinging arm model. Just to confirm, the bush is part of the sleeve gear. Will this tap out of the main bearing with ease? The gearbox is still in the bike of course. Then I need to remove the actual bush from the sleeve gear which I assume should come out quite easily with a bit of heat. Cheers

55 GF s/a

Online JulianS

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Re: Replacing bushes on gearbox mainshaft
« Reply #3 on: 05.02. 2018 09:39 »
I remove sleeve gear by stripping primary drive/clutch/primary case, then remove gearbox sprocket. At this stage you can see if it is the bushes or the main ball bearing.

Assuming the bushes then;

Remove gearbox outer cover. Remove single screw fixing inner cover then inner complete with mainshaft can be removed,leaving the inner 3 mainshaft pinions and layshaft in box. You can then remove selector shaft,layshaft, pinions and selectors leaving just camplate and sleeve gear in place.

Remove camplate. With gearbox sprocket having been already removed the sleeve gear can be tapped through the main bearing into the main gearcase and removed. The bush will either be one long single bush (like my spare pinion) or 2 separate ones (most likely) the inner bush being drilled with oilways to coincide with the drillings in the pinion.

The bushes are pressed in they should not come out that easily. You may be able to drift them or you may need to slit them lengthways first.

Having pressed in the new ones they will very likely need to be reamed or honed to fit your mainshaft.

If it is the ball bearing then the gearcase will need removing to replace.

In any case replace the oil seal.

Online berger

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Re: Replacing bushes on gearbox mainshaft
« Reply #4 on: 05.02. 2018 13:52 »
you might find that if the bushes are really worn the mainshaft will also be worn so to do a good job the shaft could be ground and new bushes made , a friend had this done but the downside was £120 at engineers shop the only problem you might have is the unworn part of the mainshaft and trying to get a good fit on the inner bush once its passed the high spot on the mainshaft

Offline chaterlea25

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Re: Replacing bushes on gearbox mainshaft
« Reply #5 on: 05.02. 2018 17:25 »
Hi All
If a one piece bush is fitted it needs to be bored oversize where the gap was between the original bushes
I once sized a one piece bush one size the entire length It tightened up after a mile or two *problem*
My theory is that the gap/ relief holds a drop of oil that helps lube the outside bush

A stepped piece of round steel bar turned to fit inside the bush and just under the bush O/D is best to use to press out the old and in the new bushes, a press is useful for this
Its easy to damage the new bushes *sad2*

John
1961 Super Rocket
1963 RGS (ongoing)

Online KiwiGF

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Re: Replacing bushes on gearbox mainshaft
« Reply #6 on: 05.02. 2018 22:58 »
Here is a long thread with lots of info on sleeve gears, including some pitfalls, I had to re do the job, I think due to being supplied duff bushes first time around *problem*

https://www.a7a10.net/forum/index.php?topic=5202.0
New Zealand

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Offline Slymo

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Re: Replacing bushes on gearbox mainshaft
« Reply #7 on: 28.01. 2019 02:19 »
Ok so in the same position with my 58SR. Clutch was lifting up and down so stripped the box to discover the oil holes in the pinion were blocked and the bush had been running dry. They appear to be two steel backed bronze bushes pressed in either side of a land. Either that or there is a steel spacer in the middle of the two bushes. Two questions :
1. Is it a land and part of the pinion or is it a spacer?
2. Can I replace it with a stock phosphor bronze bush from the local bearing suplliermor does it neednto be a steel sleeved oem part?
Cheers Simon
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Offline Slymo

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Re: Replacing bushes on gearbox mainshaft
« Reply #8 on: 28.01. 2019 04:12 »
Question 1 is answered. It is clear through now thanks to the mighty Myford.
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Online morris

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Re: Replacing bushes on gearbox mainshaft
« Reply #9 on: 28.01. 2019 12:33 »
2. Can I replace it with a stock phosphor bronze bush from the local bearing suplliermor does it neednto be a steel sleeved oem part?
Cheers Simon
Yes you can but they may/will need reaming to size ( about .003in should be ok).
Leave a space between both. This will hold some oil for start up.
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Offline Slymo

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Re: Replacing bushes on gearbox mainshaft
« Reply #10 on: 13.02. 2019 08:37 »
Job all done. Very satisfactory thanks for the advice. :)
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