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Gearbox: Loose Main Roller Bearings


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#1 Projectmini_kwt

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Posted 19 March 2019 - 08:23 PM

I have come across a little concern which either means i have to throw 3 gearboxes out if concern is legit. I was checking the bores for the double main roller bearing and testing for fitment i found the bearing actually has a loose side play left to right, I can push the bearing through my with hand pressure and nothing more. Now i know the horse shoe and shims hold it in place but i still dont think it should move that easily. Both boxes are exactly the same and thats why i am asking it is strange all three are exactly the same. I have tried 2 new roller bearings and the old ones from the respect boxes and all seem to be more or less the same. Does it mean the bore has been shaved too much by lack of maintenance? These are second hand boxes

Thanks!!

#2 Moke Spider

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Posted 20 March 2019 - 07:44 AM

The Bearing should be a 0.002 to 0.0025" interference fit in that tunnel.

 

I have found some of the late Gearbox Cases though have less to the point where the Bearing floats, as you've found.

 

It's critical that this Bearing be firmly anchored in the Case, if it's not, it can lead to the Gearbox jumping out of gear and eventually, broken teeth off the Crown Wheel and / or Pinion.



#3 Projectmini_kwt

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Posted 20 March 2019 - 12:06 PM

Hi chris

As always you are a great help! So it seems to be a thing with the later boxes! I can confidently anchor it in left to right movement due to the fact the shims, cir clip and horse shoe will do that work, but my concern is due to the lack of interference and ability to float with my hand the is a risk of the outer sleeve spinning inside the bore and causing even more damage, so i guess 3 boxes are no good!!

#4 Moke Spider

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Posted 20 March 2019 - 05:56 PM

No worries :proud:

 

Yes, the bearing may also spin. The 'C' Plate is not at all an effective way of anchoring the Bearing as the Bearing does not have a flange not does it fit up against a machined register in the case, but only has a thin circlip, which in itself is not positively locked to the Bearing.

 

The only suitable fix I can see for this is to have the Bearing Tunnel built up with some weld and machined back to size.



#5 DeadSquare

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Posted 20 March 2019 - 06:58 PM

This is crying out for a good bodge !

 

Have you got any way of very accurately measuring the bearing outside diameter and the oversize hole.

 

If so, divide the difference by two and buy the nearest thicker shim. 

 

Roll the shim into a tapered tube, insert it in the hole and trim it to the appropriate diameter.

 

Put the bearing in the tapered tube and press it into the shim filled hole.

 

Trim excess shim with a sharp object.



#6 Projectmini_kwt

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Posted 22 March 2019 - 06:12 PM

Cheers dead square i have a couple of telescopic micrometres coming in so once arrive i will check the diameter. The bear have a slight difference between them but even with the bigger one it is still floating so will need to add a bit of shimming!

#7 Projectmini_kwt

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Posted 22 March 2019 - 06:14 PM

Chris sorry for sounding silly but you mean 0.002 milimeter or 2 thou. Measuring In milimiter makes more sense as 2 thou would make it a very tight squeen

#8 carbon

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Posted 24 March 2019 - 05:48 PM

This is crying out for a good bodge !

 

Have you got any way of very accurately measuring the bearing outside diameter and the oversize hole.

 

If so, divide the difference by two and buy the nearest thicker shim. 

 

Roll the shim into a tapered tube, insert it in the hole and trim it to the appropriate diameter.

 

Put the bearing in the tapered tube and press it into the shim filled hole.

 

Trim excess shim with a sharp object.

Would Loctite 'bearing fit' or similar also be an option here to taking up the slack and preventing bearing-to-casing movement?



#9 Shooter63

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Posted 24 March 2019 - 06:17 PM

Or just centre punch the hole at equal spacing,that will raise the surface then use bearing fit

Shooter

#10 Moke Spider

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Posted 24 March 2019 - 07:05 PM

Chris sorry for sounding silly but you mean 0.002 milimeter or 2 thou. Measuring In milimiter makes more sense as 2 thou would make it a very tight squeen

 

0,002" (imperial). Being an Aluminum Casing it will expand at a greater rate than the Steel Bearing. Some tables actually suggest a tighter fit but this could result in cracking of the web.

 

 

 

This is crying out for a good bodge !

 

Have you got any way of very accurately measuring the bearing outside diameter and the oversize hole.

 

If so, divide the difference by two and buy the nearest thicker shim. 

 

Roll the shim into a tapered tube, insert it in the hole and trim it to the appropriate diameter.

 

Put the bearing in the tapered tube and press it into the shim filled hole.

 

Trim excess shim with a sharp object.

Would Loctite 'bearing fit' or similar also be an option here to taking up the slack and preventing bearing-to-casing movement?

 

 

Some of the Lower Strength Loctites will gap fill to a point, but also keep in mind that, as mentioned, the Bore in the Casing will get bigger as the Oil heats up, so any gap will increase.

 

Dead Square's suggested 'bodge' may have some merit, not one I've tried, but I know 'speedy sleeves' are available for field repairs of worn Bearing Housings, which really are a formed shim.

 

 

Or just centre punch the hole at equal spacing,that will raise the surface then use bearing fit

Shooter

 

My experience with doing this (not in a Gearbox but on hubs) is that while the Bearing feels tight going in, in Service and in short time, the raised pips from the centre popping only get pressed back in.



#11 Projectmini_kwt

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Posted 24 March 2019 - 09:21 PM

Thanks for all the suggestions, it will be good to keep this post going as finding info on specific areas is difficult and most repair/rebuild manuals/videos assume all is going hunky dory! I just recieve my bore micrometres today i ll get measuring and post the progress.

Will the interference be the same for both 3rd motion and 1st as well as the cruch on the diff bearings? So 2 thou?

To be continued ....




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