F.D. Failure Caught Early - BMW Luxury Touring Community
 
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post #1 of 9 Old Aug 14th, 2011, 4:32 pm Thread Starter
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F.D. Bearing Failure Caught Early

Performed the 60K scheduled service on my 2000 LT and the final drive drain plug was clean except for the usual "paste" thats been found at every 12K service since I bought the bike at 19K miles.

Hard to say when I started sensing a very subtle vibration from the rear (maybe well before the 60K service) but it was enough to make me pull the drain plug 300 miles after the 60k service and I found just a few very small, very shiny metallic flakes. Refilled the final drive and did another 300 miles. Checked it again and sure enough, a few more flakes. That was all I needed to see. Wheel play was present.

Drop check on the new bearing showed .28mm clearance. Replaced the .61mm factory installed shims with .35mm shims.

I cut the suspect brg apart and sure enough....see pics. Classic case of flaking/spalling in just one spot in the center of the raceway. This case does not indicated a preload issue to me as much as perhaps a brg quality issue (I believe that is BMW's position on the early model failures).

Good reading if interested... http://www.vibanalysis.co.uk/technical/contents.html

Anyway, I'm back on the road and the bike is noticeably smoother....
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Last edited by giarcg; Aug 14th, 2011 at 5:17 pm.
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post #2 of 9 Old Aug 14th, 2011, 10:59 pm
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Re: F.D. Failure Caught Early

Good catch and thanks for the picture. Yes, it does look like a quality issue.

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post #3 of 9 Old Aug 15th, 2011, 1:15 am
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Re: F.D. Failure Caught Early

While the large spot looks close to center, I believe I see offset damage leading up to or away from the large spot consistent with excessive pre-load. Maybe a little of both issues going on there. Good catch.


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post #4 of 9 Old Aug 15th, 2011, 7:01 am
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Re: F.D. Bearing Failure Caught Early

Thanks for posting this. Your sensing a "very subtle vibration" which led you to check the drain plug and find "a few very small, very shiny metallic flakes" is probably the best early detection method available to us short of final drive disassembly or very frequent lube changes.

Also, thanks for the link to bearing failure analysis. I've read that and similar descriptions with interest before. I think our final drive is best represented by figure #10 showing both axial and radial loading. However, the loading of our final drives, being on a motorcycle, is going to be much more dynamic than would be a similar axial and radial loaded setup in a static machine. I have tried to correlate the spalling pattern with the final drive setup with limited success. Spalling of the both the inner (the rotating race in the FD) and the outer race (the non-rotating race in the FD) has always seemed to be randomly located. There is just more of it as the bearing degrades. I suspect that once the pitting process starts, and metal flakes are being generated, the spalling will continue randomly, where ever the metal flakes happen to get caught between the balls and races. I think that's why the neat diagrams of bearing analysis shown in the document you linked to don't correlate well with failed bearings from failed drives that I have seen.

I've cut open quite a few of these bearings in all stages of failure and your speculation that bearing quality is a factor stands to reason. More recently I have seen bearings where the races were severely worn with out pitting. In these cases there is an increase of fine metal particles (grey fuzz) on the drain magnet but not the shiny metal flakes. These bearings also had excess preload, and the excess wear of the groove was the side which correlated with the axial loading. I have speculated that these bearing that are showing severe wear in the grooves but no pitting were made of better quality metal and were standing up to the stress of excess preload better than earlier bearings.

Consequent to these observations, I agree with you that bearing quality may be a factor in these failures, but I still maintain that excess preload is a significant factor. Among other arguments, perhaps the most salient fact is that if it were purely a bearing quality issue the 90% or more of bikes that have not failed would have failed. Many of those bikes have gone 100K miles without problems and they are running the same bearings as those that failed.

No doubt BMW went to their bearing manufacturer and talked about the issue, and very likely the bearing manufacturer looked at their metallurgy and maybe improved the metal going into the bearings. If we are getting better bearings now, that's really good news. Maybe we are. But unless properly setup they are going to fail.

Based on my observations, I think your statement: "This case does not indicated [sic] a preload issue to me as much as perhaps a brg quality issue ...." reaches the wrong conclusion. I think the evidence shows that it is more a preload issue than a bearing quality issue, although I agree bearing quality may play a role.

This has been much discussed over the years on this site by members who have training in mechanical engineering and this post is a revisitation of an old discussion.

Anyone who has a failed final drive should be cautioned not to just rebuild their drive with a new bearing, thinking that the new bearing will be of better quality. Proper assembly is required.


Quote:
Originally Posted by giarcg
Performed the 60K scheduled service on my 2000 LT and the final drive drain plug was clean except for the usual "paste" thats been found at every 12K service since I bought the bike at 19K miles.

Hard to say when I started sensing a very subtle vibration from the rear (maybe well before the 60K service) but it was enough to make me pull the drain plug 300 miles after the 60k service and I found just a few very small, very shiny metallic flakes. Refilled the final drive and did another 300 miles. Checked it again and sure enough, a few more flakes. That was all I needed to see. Wheel play was present.

Drop check on the new bearing showed .28mm clearance. Replaced the .61mm factory installed shims with .35mm shims.

I cut the suspect brg apart and sure enough....see pics. Classic case of flaking/spalling in just one spot in the center of the raceway. This case does not indicated a preload issue to me as much as perhaps a brg quality issue (I believe that is BMW's position on the early model failures).

Good reading if interested... http://www.vibanalysis.co.uk/technical/contents.html

Anyway, I'm back on the road and the bike is noticeably smoother....
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Last edited by CharlieVT; Aug 15th, 2011 at 9:58 am.
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post #5 of 9 Old Aug 15th, 2011, 9:18 am
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Re: F.D. Failure Caught Early

If there is only one "wart" on the inner race, it may have been caused by a single particle of contamination on initial assembly being rolled thru the bearing. The other minor scuffs are from the more recent generated contamination.
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post #6 of 9 Old Aug 15th, 2011, 11:29 am Thread Starter
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Re: F.D. Failure Caught Early

Greetings CharlieVT, I have followed your posts and others regarding this subject over the last few years and am well aware of your interest in this subject. In a weird way I've been anxiously awaiting the day I had a reason to tear into this final drive so I could see what everyones been talking about. I'm just glad I could deal with it in my shop as opposed to the side of the road in Moosebutt, wherever (grin).

I felt compelled to share my findings due to the fact that the failure was caught early enough to see where the initial spalling occurred. I'll leave it up to interested readers to come to their own conclusions regarding radial and axial loads based on the location of the spalling (dead center of the raceway) as I have.

I'm glad you acknowledged the possibility of quality playing a role in this case. My professional background is primarily with a large domestic manufacturer of turbine engines. Most of my time has been spent in assembly and testing of the large high-bypass turbo fan engines you would find on 737 thru 777 aircraft. Obviously bearings are a key component in these engines. I can't tell you how many times over the years bearing quality issues have caused increased inspections or fleet removals due to suspect quality issues. One failure can result in dozens of removals in a serial number range, just because they could be suspect.

Regarding your statement -

"Among other arguments, perhaps the most salient fact is that if it were purely a bearing quality issue the 90% or more of bikes that have not failed would have failed. Many of those bikes have gone 100K miles without problems and they are running the same bearings as those that failed."

A quality issue doesn't have to affect a whole part number's production. A design issue might but not a quality issue. It could be a certain percentage or just one. A good example is the bearing failure that caused the Sioux City DC-10 crash... believed to be a one-off bearing defect.

As I understand it BMW purged the supply chain of the original 19 ball bearing while introducing the 17 ball bearing. Quality concerns drove this and after some time they reintroduced the 19 ball bearing (quality concerns addressed) with the same P/N as the original one. The 19 ball design was preferable to the 17 for load reasons. All this seems consistent with what I've seen in the aviation world.

Regarding this -

"I think your statement: "This case does not indicated [sic] a preload issue to me as much as perhaps a brg quality issue ...." reaches the wrong conclusion. I think the evidence shows that it is more a preload issue than a bearing quality issue, although I agree bearing quality may play a role."

I know that excessive pre-load is a popular failure mode and may very well be the source of most issues. It's good that you once again recognize a potential quality issue. Its important to point out that my opinion is based on this specific case...my case. The only one I have first hand knowledge of. I'm not generalizing here.

And finally -

"Anyone who has a failed final drive should be cautioned not to just rebuild their drive with a new bearing, thinking that the new bearing will be of better quality. Proper assembly is required."

Well, never mind.

Once again I hope these early failure pics are of some value to those interested.

Last edited by giarcg; Aug 15th, 2011 at 11:54 am.
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post #7 of 9 Old Aug 15th, 2011, 11:52 am
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Re: F.D. Failure Caught Early

Greetings giarcg,

Thank you for a thoughtful post on the subject. Much of what I think I know about K1200LT FD failures has come from experienced professional mechanics (technicians), mechanical engineers, and others who have taken the time to write on the subject. Your contribution from your professional perspective is much appreciated. My contribution has been primarily to take apart a bunch of these failed FDs, try to observe what things looked like inside the drive and relate those findings to what the rider reported regarding symptoms and history of the failure.

One consistent finding of failed bearings that were spalled in a range of severity and distribution around the races and roller balls has been preload shim thickness that was well in excess of the specification in the BMW Service Manual. I noted with interest that your orginal post in this thread stated: "Drop check on the new bearing showed .28mm clearance. Replaced the .61mm factory installed shims with .35mm shims. "

I'm curious what method you used to calcuate your shim thickness. I don't know what "drop check" means. I wonder if you would explain what measurement method you used?

Your post indicates that you had a bearing that went 60K miles. And when you rebuilt it your measurments indicated your shim should be 0.26mm less than what was in there.
That is consistent with the majority of failed bearings I have seen, i.e. the ones that fail have more preload originally than the rebuild called for.

Again, thanks for taking the time to post a thoughful reply.

Warm Regards,
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post #8 of 9 Old Aug 15th, 2011, 12:52 pm Thread Starter
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Re: F.D. Failure Caught Early

Charlie,

"Drop check" is kind of an industrial term used in the measurement of vertical assemblies. It's a measurement that usually verifies if two or more components are seated or joined together correctly. While I've been out of engine assembly for some time old habits, and terminology, persist.

I include the clearance and shim data for people such as you to use for comparative reasons. I know there are perhaps more that a few folks here that have, or will be, replacing this bearing and might find it useful.

Without access to BMW tooling and fixtures I measured the clearance between the installed new bearing outer race and the bearing seat in the cover as an assembly. Then simply added the prescribed preload. I would have liked to compare that result with what the BMW procedure would have produced but again, without their fixtures I couldn't. Curious to know if the circular fixture that supports the crown gear assembly simply keeps it centered or also seats the roller bearing. Obviously this would have great implications for the comparison.

Good to know my results are consistent with what you have seen. I wish I had the presence of mind to measure the clearance of the old bearing prior to disassembly. Although it would ultimately be of no use due to the wear or "slop" in the bearing.
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post #9 of 9 Old Aug 15th, 2011, 7:51 pm Thread Starter
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Re: F.D. Failure Caught Early

Quote:
Originally Posted by giarcg
A good example is the bearing failure that caused the Sioux City DC-10 crash... believed to be a one-off bearing defect.
The failure that caused the crash was actually a defect in the stage 1 fan disk, not a bearing. My error... I had bearings on my mind at the time.
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