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Discussion Starter #1
More Final Drive fun:

This is from a 2000 K1200LT with 55K miles on it. I don't know any other history other than it started grinding. Here's what L.D. who owns the bike said about it: "Just started making a grinding noise with a varying frequency. Grind stop, grind, stop, etc.
Hear and feel it best at low speeds. Does it whether under load or free wheeling."

Classic crownwheel bearing failure. I've done upwards of 30 of these now and I have come to expect that the existing shim is a thick one. Yup, the original shim was 0.80mm in this case. I now have a collection of about 20 shims ranging from 0.60mm to 1.00mm which I don't seem to have a use for as I usually need a preload thickness less than 0.60mm.

My calculations for the new bearing in this case indicates a 0.50mm shim. Again, I find that drives with failed crownwheel bearings have been shimmed with too much preload. I believe with increasing conviction that the cause of many (most or all?) crownwheel bearing failures is improper (exessive) preload setup at the factory. And I believe that anyone who replaces a failed crownwheel bearing without recalculating for preload shim thickness is inviting another failure.

Attached are pics of the trashed crownwheel bearing and of the drain plug.
Also attached is a MS Exel spreadsheet of calculations used in rebuilding this drive.
 

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I'm in the middle of rebuilding my FD, and the shim I removed was 0.75 to 0.80 mm, best I can tell (0.033 inch is what I measured, with dial indicator). I am noticing burrs on the shim, possibly from the punch that was used in manufacture. With the shim laying flat on my table, the inner edge has a burr pointing down, and the outer edge has a burr pointing up. Also the outer edge is not flat on the table, whereas the inner edge is. I measured 0.038 inch thickness this way, and 0.042 inch when I flipped it over (that's how I first noticed the lack of planarity. Compensating for the angle, I measured the 0.033 inch minimum thickness. Using a digital caliper, I measured 0.78 mm, but not sure if the burrs are included in that measurement or not. The burr is enough to explain the mysterious cut I found on my fingertip after dismantling the drive.

Since you have a large collection of similar size shims, Curtis, do any of those exhibit a burr, or the non-planarity I'm describing?
 

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Discussion Starter #3 (Edited)
I have seen the burr you describe in some cases. I'm curious is your drive a failed drive or a preemptive rebuild?
For purposes of visualizing the shim having an "up" and a "down" side, imagine the FD cover sitting on your bench with the inside of the cover facing up. The shim sits in the recess the is the seat for the crownwheel bearing. When the shim is sitting in this recess the "up" side is the side you are looking at and the "down" side of the shim is facing down against the FD bearing seat.
The shim is loaded when the cover is bolted onto the FD housing. This pressure can cause the outer edge of the shim to be bent up a little inside the cover and the inner edge bent down by the bearing race into the opening of the FD cover. This is what creates the burrs you are describing.
However, I have noticed this mostly on the thinner shims, and on FD where the bearing has failed and the rider continued to ride for a while. This can result in a spun bearing. When the outer race spins in the cover, the shims can become quite distorted.
In the case of the thinnest shim (0.15mm) which is used in combination with other shims to get a 0.05mm thickness, there can be some interesting distortions. Attached it a pic of a 0.15mm shim from a drive in which the outer bearing race spun in its seat. There is an oil channel in the FD cover which "catches" the shim as it is spinning, and crumples the shim as shown here.
Any shim that has had this kind of event may have burrs which, as you have noted interfere with accurate mic'ing of the shim thickness. As far as lying flat in one plane, even new shims don't; this is much more noticable with the thinner shims as they bend very easily, the thicker ones resist bending more. No matter, once the shim is in place and the FD cover it torqued into place, the shim will be flattened out.
I imagine it is a little difficult to measure shim thickness with a dial indicator, a caliper micrometer would be easier. Using a micrometer I have found that shims often vary in thickness at different locations around its circumference; the variation can be as much as 0.03mm.
HTH



sparky_k1200lt said:
I'm in the middle of rebuilding my FD, and the shim I removed was 0.75 to 0.80 mm, best I can tell (0.033 inch is what I measured, with dial indicator). I am noticing burrs on the shim, possibly from the punch that was used in manufacture. With the shim laying flat on my table, the inner edge has a burr pointing down, and the outer edge has a burr pointing up. Also the outer edge is not flat on the table, whereas the inner edge is. I measured 0.038 inch thickness this way, and 0.042 inch when I flipped it over (that's how I first noticed the lack of planarity. Compensating for the angle, I measured the 0.033 inch minimum thickness. Using a digital caliper, I measured 0.78 mm, but not sure if the burrs are included in that measurement or not. The burr is enough to explain the mysterious cut I found on my fingertip after dismantling the drive.

Since you have a large collection of similar size shims, Curtis, do any of those exhibit a burr, or the non-planarity I'm describing?
 

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Hi Curtis,

Great thesis work in final driveology! Now I, and I'm sure others, are wondering what's the thickness of their shims?!?!?!?

Thanks again,
Jer
 

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They may not be owning up to it, but I'll bet they've got a guy watching Curtis like a hawk!
You can bet someone's taking note of his work and findings and testing his theory. I would suggest strongly that we all owe a great deal of thanks for his work.
 

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Hey, Curtis - talking with a coupla folks this morning at *$$, the question came up as to whether you have rebuilt a failed FD from an '05 or newer LT? I couldn't remember, and didn't take the initiative to search - thus the question. Have ya??
 

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Mine was a full fail. 1500 miles ago (at 90K miles), changed oil, no indication of metal in oil other than the usual tiny collection of dust on magnet . No play in wheel.

Noticed slight noise, as if riding over gravel, or the rear brake disk dragging. Within a mile, it changed to a grind-stop-grind-stop...as if I was riding in and out of the rumble strips they carve into the shoulders of highways. I took chance and rode it the remaining 2 miles home. Right turn, 2 lefts, and one right into driveway. (it seemed to make less noise during the turns). Up on the center stand, it was obvious to me that the bearing was shot. No sign of seal breach. Next morning, found about a teaspoon of oil had leaked out, down tire, and onto ground. Drained oil to find it very dark, and with a burnt smell. Lots of mud on drain plug magnet, nothing gritty, but did look shiny when I wiped it on a rag.

Found a great video on this site showing the rebuild ( Thanks Curtis! ), and after a viewing or 3, felt I could tackle this job. Got the drive open, and found much less shrapnel than seen in the video, less than L.D.'s, and less than most of the others I've seen posted on this site. Maybe a pea-sized collection of flakes/mud also found spread out inside. Disassembly seemed easier than was shown in the video. Did a first round of parts washing, and everything else looks good. Bearing is off now, and my schedule has been so busy, I haven't had time to even attempt to procure parts.
 

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Discussion Starter #9 (Edited)
fpmlt said:
They may not be owning up to it, but I'll bet they've got a guy watching Curtis like a hawk!
You can bet someone's taking note of his work and findings and testing his theory. I would suggest strongly that we all owe a great deal of thanks for his work.
Nah, BMW knows way more about what's going on with these drives than I do.
They just made a marketing decision not to openly acknowledge the problem.
Whatever the problem was they've evidently fixed it.
Let's face it, there was no way they were going to recall every LT and rebuild or replace the FDs, unless some Gov't agency really held their feet to the fire.

I happen to think they'd have been smart to just put out an extended warranty on all the FDs out there, rather than take the approach that they did. I read reports of a few FD fixed that were slightly out of original warranty, but for the most part they seemed to deny the issue; if you had a FD failure out of warranty, well... that was your problem. That approach might have been good "damage control" for a company's reputation years ago, but in this age of internet information sharing I think they just hurt their own reputation.
How much would putting an extended warranty on final drives, say to 100,000 miles have cost them versus how much did denying they had a bad batch of drives cost them in sales? But hey, I'm sure they've analyzed that too.
 

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Discussion Starter #10
Dick said:
Hey, Curtis - talking with a coupla folks this morning at *$$, the question came up as to whether you have rebuilt a failed FD from an '05 or newer LT? I couldn't remember, and didn't take the initiative to search - thus the question. Have ya??
Hiya Dick,
You know, my records are getting better but aren't that good. Going from memory, I'd say I've had a 2005 drive here, but it might have been a preemptive rebuild on a drive that someone bought as a spare.

I'm pretty darn sure that I haven't seen a crownwheel bearing failure on a 2006 or newer. Most of 'em are the early 99-02 years. Sad thing is, some of the failures are drives that failed more than once, having been repaired by just replacing the bearing, only to fail again. I wonder how many of those there are.... I know of a few.

If the motive behind the question is "how reliable is the final drive on my 05 or newer bike?" the answer it is probably a very reliable drive. Much better odds than the earlier ones IMO. Remember that there were a few drives in the 05 period which had a tapered roller bearing problem which is very different from the crownwheel bearing problem of the earlier bikes.

BUT... I'm sticking my neck out here. Most of what I just said is opinion based on reading posts on this site, not based on what I have seen in failed drives.
 

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CharlieVT said:
Hiya Dick,
You know, my records are getting better but aren't that good. Going from memory, I'd say I've had a 2005 drive here, but it might have been a preemptive rebuild on a drive that someone bought as a spare.

I'm pretty darn sure that I haven't seen a crownwheel bearing failure on a 2006 or newer. Most of 'em are the early 99-02 years. Sad thing is, some of the failures are drives that failed more than once, having been repaired by just replacing the bearing, only to fail again. I wonder how many of those there are.... I know of a few.

If the motive behind the question is "how reliable is the final drive on my 05 or newer bike?" the answer it is probably a very reliable drive. Much better odds than the earlier ones IMO. Remember that there were a few drives in the 05 period which had a tapered roller bearing problem which is very different from the crownwheel bearing problem of the earlier bikes.

BUT... I'm sticking my neck out here. Most of what I just said is opinion based on reading posts on this site, not based on what I have seen in failed drives.
Thanks, Curtis. Just making conversation wuz the motive behind the question. Came up during a discussion of how confident I am now that ole Toad has benefitted from your 'overhaul technique' and the many threads that definitely should be filtered back to the leather chair users at the factory. ;) Your thoughts on the belief that the original shimming (process) is suspect in FD failures that you have done remedial work on. That prompted the question about the '05s that you may have handled. Thanks again for your thoughts. ;)
 
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