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+--- Thread: Gearbox intershaft bush (/showthread.php?tid=2010)
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Gearbox intershaft bush - jansens - 13-11-2018
I am busy rebuilding my gearbox (with close ratio gears) and have replaced the inter shaft roller bearing which is fairly worn with the plain bush. It slide over the shaft when I tested it out of the shaft and it pressed into the first motion gear fine.
But now I find the shaft won't slide all the way in. It seems to bind up on the last few mms. Even though I can't measure any difference in the shaft diameter you can see where the rollers have polished it a little and a bit of engineers blue wiped on the shaft showed that it is rubbing at that point.
It must be very close to fitting. What is the best way to fix this?
Also how is the best way to separate the two halves of the lay gear cluster once the clip is removed?
Simon
RE: Gearbox intershaft bush - squeak - 13-11-2018
Hello Simon, is there an hydraulic lock that could be sorted with an escape groove filed in the bush ? regards Russell
RE: Gearbox intershaft bush - jansens - 13-11-2018
Hi Russell, it actually comes with grooves in it for lubrication I guess so it's not that. You can hear the air escaping as it slides home. As the shaft goes into the bush you can feel it start to bind a bit like you feel with a taper in a lathe or drill if that makes sense.
Simon
RE: Gearbox intershaft bush - Steve Hainsworth - 14-11-2018
(13-11-2018, 11:59 PM)jansens Wrote: Hi Russell, it actually comes with grooves in it for lubrication I guess so it's not that. You can hear the air escaping as it slides home. As the shaft goes into the bush you can feel it start to bind a bit like you feel with a taper in a lathe or drill if that makes sense.
Simon
Hi Simon
the bush may have pinched a little at the far end of the hole. if you have a parallel reamer the right size you could relieve it. I can help you with this if you call round.
I have used dowel pins with a groove ground lengthwise to make a reamer before to do this sort of job. if its only slightly tight- lapping with "Brasso" will often suffice. Cheers Steve H
Hi Simon I have just reread your first post. I seem to remember the Retro-fit Bush has external oil grooves as well as internal, which means that it rotates within the first motion (input) shaft as well as turning on the third motion shaft (output) so it has twice the bearing surface and acts in the same way as the roller race it replaces. Is your Bush made this way ? if not I think it should if it is to last.
Have you a photo to share?
Cheers Steve H (again)
RE: Gearbox intershaft bush - Chris KC - 14-11-2018
I'm struggling a little to know what to make of this. The bush should be a (small) running clearance on both shaft and bore, so if it will assemble freely to both in the 'dis-assembled' condition it suggests something is awry on assembly.
RE: Gearbox intershaft bush - Hedd_Jones - 14-11-2018
Sounds like some timesaver and a little lapping is required
RE: Gearbox intershaft bush - Hugh Barnes - 14-11-2018
And for those who haven't heard of it, Timesaver is a lapping compound that works very well. I have used it in various places, I think having first picked up on it after an earlier post by Hedd. Craftmaster Paints supply it...
RE: Gearbox intershaft bush - jansens - 14-11-2018
I've always been told bushes that are a push fit will close up slightly once pushed in place. This one I definitely had to push into the first motion shaft (using a vice and a socket as a pusher on the face) but it wasn't hard to do. When I checked it on the shaft I might not have made sure it went all the way down. I've been caught out with that before with a spigot bush on an MGB which prevented me from getting the gearbox to mount as the gearbox input shaft wouldn't fit into the bush in the crank. I ended up having to remove the bush with the toilet paper and wooden plug and BFH method!
It definitely doesn't turn as you mention Steve. Turbocharger bushes work that way and have quite a bit of play but then they run lots of oil pressure too. This is definitely a tight fit in the first motion shaft. I will try the Brasso method as it feels only just tight. I suspect the problem is the shaft and where it is worn not the bush.
Never heard of that Timesaver stuff so looked it up. Seems like one of those things that's been around for ever (longer that Austin 7s even!) and does work for certain things very well. If I could get it I would definitely try it but of course not available locally and once you find someone who will send overseas it costs so much not to be worth while.
Even if I have to lap it in it will still be far tighter than the worn bearing that came out so I think it will work fine. The other thing I considered was polishing the gear shaft but only where it isn't worn by the old roller bearing. I would have thought the bush was made to fit based on an unworn size though.
Simon
RE: Gearbox intershaft bush - Terrytuned - 14-11-2018
Hi Simon this is not a problem you find this with most of these bushes, check for any machining burrs polish out the bore of the 1st motion
shaft and the outer side of the bush the fit is not critical it just has to freely slide on both surfaces. If you as fitting a set of c/ratio
gears you usually find the bore of the 1st motion shaft has shrunk and needs polishing out with a small emery drum.Parting the
layshaft depends on the fit some you can knock apart with a shouldered brass punch or you may need to press it apart.
Terry.
RE: Gearbox intershaft bush - jansens - 14-11-2018
Thanks Terry, the bush I have looks exactly like that. I'll figure out some kind of press to get the layshaft apart. Knocking it with a drift got it a mm or so. I just wanted to make sure there was no trick like with the king pins!
Simon