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Enjoy The Ride
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Discussion Starter #1
I took my original FD off a few weeks ago with 88,000 miles on it. I have a new spare that I put on. I made what I think is a universal fixture to hold it (it should fit other model bikes as well). The preload spec. for the LT is .002 to .0039. My original FD had .0035 from the factory. The new bearing with the same shim has .0027 preload.

I took the old bearing apart and viewed it through my 8 diopter lens. Both bearing races & all the balls look perfect not a single mark on them. Over the next few days I'll look at everything with our microscope at work.

The method I used to check the preload is the same way CharlieVT does it in his video. When I install my original FD I'll check the preload on my spare. I have misplaced my camera & hopefully I'll have some pictures when I check my spare.

I do think this is the best way to check preload using all the exact parts that will be used in the FD.
 

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Hiya Dave,

Read your post with great interest. :thumb:
Curious, were the old bearing and the new bearing the same manufacturer? I suspect both were the German FAG 61917.C3 bearings, correct?

I am interested in a pic of your rebuild fixture.

Interested in all your observations, thanks.
 

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I too will be interested in the photos. And just curious: did you change it out just as a pre-emptive measure, or were you showing any signs of wear?
Also wondered for a while, given the span of acceptable preload measurements, is it best to move toward the high or low side?
 

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Discussion Starter #4
Hi Curtis: Yes they were both the same quer er I mean Fag 61917.c3 bearings. Even though my bearing was in perfect condition I'm still glad I rebuilt it so I could check it all before it actually needed it.

BTW the gas grill worked fine. ;)
 

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Discussion Starter #5
fpmlt said:
I too will be interested in the photos. And just curious: did you change it out just as a pre-emptive measure, or were you showing any signs of wear?
Also wondered for a while, given the span of acceptable preload measurements, is it best to move toward the high or low side?
It was pre-emptive. I wanted to be able to rebuild it while it was still in good condition so I could measure the factory preload. As far as the high or low side of the preload all I know is that after looking at all of CharlieVTs shims & mine there is quite a bit of movement shown on the shim.

Based on that I would probably try to make it on the high side but not over the limit at all.
 

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saddleman said:
It was pre-emptive. I wanted to be able to rebuild it while it was still in good condition so I could measure the factory preload. As far as the high or low side of the preload all I know is that after looking at all of CharlieVTs shims & mine there is quite a bit of movement shown on the shim.

Based on that I would probably try to make it on the high side but not over the limit at all.
Dave, did your shim show signs of having spun? I have seen that on failed drives I have opend and the scoring of the shim was usually assocated with scoring of the bearing seat in the FD cover. I've seen lots of that in the failed drives I've opened but would be surprised to see it in a drive that was opened preemptively.

With respect to preloading on the high side or low side, I think that is anybody's guess. BMW specifices a preload from 0.05 to 0.10mm. I suspect that if you are accurately within this range, it probably won't matter if you are at the high end or low end of the range, but that's just an opinion. My guess is that being a little overshimmed is probably going to be worse that being a little undershimmed. (IIRC this was suggested by one of the mechanical engineers on this site some time ago.) Like so many things about this issue, we'll probably never know.
 

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Charlie, I've watched the video and was wondering if there is any reason you can't just use a feeler gauge to measure the space between the bearing and the housing, add the desired preload to the gap and shim accordingly instead of using the dial indicator.

Ii bought a 2000 LT with 44k on it back in July and have put another 10k on it. I was thinking of doing a pre-emptive rebuild over the winter since I have no maintenance history on the bike. I sure wish I could have made your tech session.
 

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Discussion Starter #8
CharlieVT said:
Dave, did your shim show signs of having spun? I have seen that on failed drives I have opend and the scoring of the shim was usually assocated with scoring of the bearing seat in the FD cover. I've seen lots of that in the failed drives I've opened but would be surprised to see it in a drive that was opened preemptively.

With respect to preloading on the high side or low side, I think that is anybody's guess. BMW specifices a preload from 0.05 to 0.10mm. I suspect that if you are accurately within this range, it probably won't matter if you are at the high end or low end of the range, but that's just an opinion. My guess is that being a little overshimmed is probably going to be worse that being a little undershimmed. (IIRC this was suggested by one of the mechanical engineers on this site some time ago.) Like so many things about this issue, we'll probably never know.
My shim looked just like all of yours. It even had the little lip you could feel on the inside. I don't think its from getting spun but rather getting a small normal movement it goes thru between the heat cycles & high side loads. Your right on never knowing other than setting one up on the low side & one on the high side of the preload. Even then it would have to be run on the same exact conditions to tell anything.
 

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rcoolbaugh said:
I've watched the video and was wondering if there is any reason you can't just use a feeler gauge to measure the space between the bearing and the housing, add the desired preload to the gap and shim accordingly instead of using the dial indicator.........
To do a direct measurement with feeler gauges the drive would need to be assembled. When the drive is assembled, even with the oil seal not installed, access to the outer race of the crownwheel bearing is extremely limited. I don't see how you could get an accurate measurement with a feeler gauge.
 

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Thanks. I just went and watched the video again and see what you mean.
 

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FYI Dial indicators are cheap - especially inch ones. They are widely available at surplus stores etc. Harbor Freight has them new for $15 although dial indicators are a little bulky.

A dial test indicator might be a little more accurate and has the advantage that it can also be used with a cobbled up fixture to measure engine-transmission alignment when diagnosing clutch spline problems (does this mean it should be part of every BMW tool kit!). Harbor Freight doesn't seem to handle them anymore, but others should have them for 30-40 dollars.

An example is at:

http://www.mini-lathe.com/Measurement/Dial_indicators/Dial_indicators.htm#DTI
 

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Yep, I already have a couple of dial indicators, I'm just always looking for easier methods of doing things.
 

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Discussion Starter #13
When I got home from work today my camera was next to my laptop & nobody knows how it got there :wow: Anyway my flash doesn't work so I have to hold it as steady as I can. The only things I bought were 5 bolts & one nut. the rest I had gathering dust in the garage. I used wood under the FD so as not to scratch the paint.
 

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Wow! Dave,

What a neat, professional setup! Very nice looking jig. :thumb:
Some good additions to the technique with the center bolt for the dial indicator reference point, the washers under the bolts for levering the crownwheel hub up, the base plate bolted to the drive housing for the dial indicator, the fixed fulcrums for the levers.

And what a clean bench! Compare that to my work environment.....:histerica

Thanks for the photos and taking the time to share you approach to the technique. Really good stuff. I am continuing to study your pictures to try and grasp all the hints suggested by them.

Question: what is the function of the two vertical posts in place of two of the cover fasteners?

Warm regards from the deep south of Vermont.



saddleman said:
When I got home from work today my camera was next to my laptop & nobody knows how it got there :wow: Anyway my flash doesn't work so I have to hold it as steady as I can. The only things I bought were 5 bolts & one nut. the rest I had gathering dust in the garage. I used wood under the FD so as not to scratch the paint.
 

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I would guess that those two pins are for aligning the cover when assembling it Curt, but could be wrong.

John
CharlieVT said:
Wow! Dave,

What a neat, professional setup! Very nice looking jig. :thumb:
Some good additions to the technique with the center bolt for the dial indicator reference point, the washers under the bolts for levering the crownwheel hub up, the base plate bolted to the drive housing for the dial indicator, the fixed fulcrums for the levers.

And what a clean bench! Compare that to my work environment.....:histerica

Thanks for the photos and taking the time to share you approach to the technique. Really good stuff. I am continuing to study your pictures to try and grasp all the hints suggested by them.

Question: what is the function of the two vertical posts in place of two of the cover fasteners?

Warm regards from the deep south of Vermont.
 

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Discussion Starter #16
The two vertical guide pins help when I take it apart so it can't fall anywhere & it helps to align the seal & bolt holes on reassembly. I did have to run the bottom piece of wood thru my planer to get the FD to tighten down just right.
 

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Discussion Starter #17
I have looked at all of the ball bearings and the inner bearing race of the crown bearing under the microscope at work and there isn't so much as a scratch on anything. I've tried to look at the outer bearing race but I can't get it in focus. I'm going to have to cut it in half to inspect it.

I probably have spent about three hours looking in the microscope so far. The ball bearings take a long time to inspect.

If anybody has a non failed bearing I could look at I would be more than happy to look at it. I don't know what knowledge I would gain by looking at a failed bearing..
 

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saddleman said:
I have looked at all of the ball bearings and the inner bearing race of the crown bearing under the microscope at work and there isn't so much as a scratch on anything. I've tried to look at the outer bearing race but I can't get it in focus. I'm going to have to cut it in half to inspect it.

I probably have spent about three hours looking in the microscope so far. The ball bearings take a long time to inspect.

If anybody has a non failed bearing I could look at I would be more than happy to look at it. I don't know what knowledge I would gain by looking at a failed bearing..

Well at least this proves one thing...You should have left that bearing intact! :histerica You know I love ya man..... ;)
 

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Discussion Starter #19
cccpastorjack said:
Well at least this proves one thing...You should have left that bearing intact! :histerica You know I love ya man..... ;)
I expected no less from ya Jack :D God bless you & your worshippers for a good holiday season.
 
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