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Discussion Starter #1
This is so interesting, I decided to start a new thread.
(And I'll be serious, I promise....)

Bearing history:
Rebuild by BMW dealer at 36K (my understanding is that this was a preemptive rebuild, not a failed drive, but I don't know for sure).

Then new owner noticed roughness at 68K and opens the drive. Bearing retainer is broken with loose parts of retainer evident.

Bearing sent to me for forensics.

The retainer (cage) is broken in multiple places.

I cut open the outer race and take pics of the innner and outer race grooves. Very unusual, not seen by me before. Previously I have seen significant pitting of the races. In this case there are pits in the races, both innner and outer, but the pits are axial in orientation. Like I'd expect from excess pressures in pressing the bearing onto its seat. Not the kind of pitting I've seen in the past where pitting runs radially around the races.
I hope the pics show what I am talking about. The transverse lines seen in the pics are actually pitting of the races in an axial direction. These are not defects in the races that would result from wear during rotation of the bearing. They are consistent with what might happen if someone pressed the bearing onto its seat with forces directed through the outer race, through the balls, and onto the inner race. Or.... what? I don't know.....
your comments please.
RealWing
DavidS
Niel
Please comment.
This is different to me and rather strange.
Thanks and best regards from the Deep South of Vermont,
C.
 

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CharlieVT said:
This is so interesting, I decided to start a new thread.
(And I'll be serious, I promise....)

Bearing history:
Rebuild by BMW dealer at 36K (my understanding is that this was a preemptive rebuild, not a failed drive, but I don't know for sure).

Then new owner noticed roughness at 68K and opens the drive. Bearing retainer is broken with loose parts of retainer evident.

Bearing sent to me for forensics.

The retainer (cage) is broken in multiple places.

I cut open the outer race and take pics of the innner and outer race grooves. Very unusual, not seen by me before. Previously I have seen significant pitting of the races. In this case there are pits in the races, both innner and outer, but the pits are axial in orientation. Like I'd expect from excess pressures in pressing the bearing onto its seat. Not the kind of pitting I've seen in the past where pitting runs radially around the races.
I hope the pics show what I am talking about. The transverse lines seen in the pics are actually pitting of the races in an axial direction. These are not defects in the races that would result from wear during rotation of the bearing. They are consistent with what might happen if someone pressed the bearing onto its seat with forces directed through the outer race, through the balls, and onto the inner race. Or.... what? I don't know.....
your comments please.
RealWing
DavidS
Niel
Please comment.
This is different to me and rather strange.
Thanks and best regards from the Deep South of Vermont,
C.
Curtis - is there ANY possibility that the balls/retainer ring got locked/jammed in lockstep to the inner race while the outer race continued spinning the balls in place and 'scored' the inner race. Then maybe, at another outing, the reverse happened (outer race and balls/retainer ring lockstepped together)? With a broken retainer, might it be possible that pieces jammed and prevented it's movement around and around? I don't know nuttin' from nuttin' about this kind of stuff. Just blue skyin'!!!
 

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Curtis, could those have been caused when the bearing was pulled? I didn't see the process when that was done, so don't know how they did it, other than knowing that they used a torch. I tried to get it off my self, but broke my puller trying. No pounding by me, just an air impact, and the puller snapped during that.
 

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Far from being an expert, I would wonder if this might be evidence of under shimming, not enough or no preload? :confused:
 

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Discussion Starter #5
Undershimming or lack of preload did occur to me. Still wondering about that.
That the damage was caused during attempts to pull the bearing also make sense, but if correct raise a whole bunch of other questions.
 

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Very odd,
This a guess from being a mechanic for 30+ years ...
That wear pattern we would see in engine bearings where a piece of crud has lodged in the bearing preventing ball/retainer rotation, One race still is driving the balls and spinning them while contact with other race has ball spinning in place and not rolling along the surface. Basically causing the ball too do a burnout at one location.
The retainer being stalled from rotation by one area of loaded bearing causes the parts of the bearing that want to rotate normally to rip the retainer in half by fracturing or popping the rivets between segments.

This just an educated guess ...

Scott

CharlieVT said:
This is so interesting, I decided to start a new thread.
(And I'll be serious, I promise....)

Bearing history:
Rebuild by BMW dealer at 36K (my understanding is that this was a preemptive rebuild, not a failed drive, but I don't know for sure).

Then new owner noticed roughness at 68K and opens the drive. Bearing retainer is broken with loose parts of retainer evident.

Bearing sent to me for forensics.

The retainer (cage) is broken in multiple places.

I cut open the outer race and take pics of the innner and outer race grooves. Very unusual, not seen by me before. Previously I have seen significant pitting of the races. In this case there are pits in the races, both innner and outer, but the pits are axial in orientation. Like I'd expect from excess pressures in pressing the bearing onto its seat. Not the kind of pitting I've seen in the past where pitting runs radially around the races.
I hope the pics show what I am talking about. The transverse lines seen in the pics are actually pitting of the races in an axial direction. These are not defects in the races that would result from wear during rotation of the bearing. They are consistent with what might happen if someone pressed the bearing onto its seat with forces directed through the outer race, through the balls, and onto the inner race. Or.... what? I don't know.....
your comments please.
RealWing
DavidS
Niel
Please comment.
This is different to me and rather strange.
Thanks and best regards from the Deep South of Vermont,
C.
 

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Discussion Starter #7
fpmlt said:
Curtis, could those have been caused when the bearing was pulled? I didn't see the process when that was done, so don't know how they did it, other than knowing that they used a torch. I tried to get it off my self, but broke my puller trying. No pounding by me, just an air impact, and the puller snapped during that.
this is interesting info also. It had been suggested by some that the crownwheel hub might be machined too big for the bearing resulting it "stretching" of the inner race when pressed onto the seat.
It wouldn't be the first example of improper machining of the crownwheel hub, witness the spun tapered roller bearings in the 2005s.
Also, I've never had a bearing that wouldn't just drop onto the hub when heated to 250degrees F and the hub was cooled in a freezer. Your report of the bearing hanging up and not going to seat makes me wonder. Maybe the bearing wasn't quite hot enough, or maybe the hub is machined just a little too big?

Some data will never be known to us, but this sure is an interesting drive.
 

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Discussion Starter #8
Scott,
Very interesting insight, thanks for posting this. Something to consider. I wouldn't have thought of this and now that you suggest it, it seems plausible.

I also like the suggestion that damage to the races could have occured during bearing removal, but I have to reconcile that with my current belief that race and ball damage preceeds retainer failure.
Sometimes the answer is "both" or "all of the above"....

C.

motorhead said:
Very odd,
This a guess from being a mechanic for 30+ years ...
That wear pattern we would see in engine bearings where a piece of crud has lodged in the bearing preventing ball/retainer rotation, One race still is driving the balls and spinning them while contact with other race has ball spinning in place and not rolling along the surface. Basically causing the ball too do a burnout at one location.
The retainer being stalled from rotation by one area of loaded bearing causes the parts of the bearing that want to rotate normally to rip the retainer in half by fracturing or popping the rivets between segments.

This just an educated guess ...

Scott
 

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Curtis,
If you noticed, I also put in the original shim. I thought I could see circumferential scarring on both sides of that shim. Take a close look, and see if you find them. Don't know what would have caused those: perhaps light spinning during installation or removal, maybe it's normal, maybe something else?
And you're welcome (new avatar). Hate to think I insulted your sensitivities ;) or you're just an envious old phart.
 

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Discussion Starter #10 (Edited)
Hey Frank!

I got the shim, nothing particularly unusual there, seen that kind of marking before.
It is the races that really interest me.
And your avatar, that really interest me too.... not ;).
Interesting, this site.... change you avatar and all you past posts change too. Yeah, my sensitivities.

Attached is a high res pic of the outer race. Note that there is scoring from the middle of the groove to one side, and scoring from the middle of the groove to the other side.
I wondering if the bearing was abused during installation causing damage that led to retainer failure, and then damaged again during bearing removal. That would explain the scoring of the groove in different directions. My pic isn't the only example of this on the race, there are other areas that look the same. I just don't see how this could have occured during spinning of the bearing under load. Weird.....



fpmlt said:
Curtis,
If you noticed, I also put in the original shim. I thought I could see circumferential scarring on both sides of that shim. Take a close look, and see if you find them. Don't know what would have caused those: perhaps light spinning during installation or removal, maybe it's normal, maybe something else?
And you're welcome (new avatar). Hate to think I insulted your sensitivities ;) or you're just an envious old phart.
 

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What does the outer race look like?

The fact that the marking seems to be on the same pitch as the ball spacing points to initial damage during installation, not during bearing rotation. That pretty much jives with the spalling seen on my failed bearing, which a bearing engineer at SKF felt was started by light brinnelling at assembly by too much or shock forces applied.

Strange that the marking seems to be all across the race though, normal brinnelling from improper installation would cause marks on one side of the inner race, opposite side of the outer race.
 

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Discussion Starter #12 (Edited)
Thanks for this reply, David.
See my post just above with a pic of the outer race.
I think it is consistent with your suggestion of damage during installation.
And then subsequent damage during removal.
Frank reports that he broke a bearing puller trying to get the bearing off, and then a shop heated the bearing to facilitate removal.

Addendum: there is a definite "sided-ness" to the marks on the outer race. Many marks start in the center of the groove and go up the groove only to one side. There are some marks that are fairly symmetrical across the center of the groove, but there are several others that start in the center and go up one side or the other.

Thanks again,
Curtis


dshealey said:
What does the outer race look like?

The fact that the marking seems to be on the same pitch as the ball spacing points to initial damage during installation, not during bearing rotation. That pretty much jives with the spalling seen on my failed bearing, which a bearing engineer at SKF felt was started by light brinnelling at assembly by too much or shock forces applied.

Strange that the marking seems to be all across the race though, normal brinnelling from improper installation would cause marks on one side of the inner race, opposite side of the outer race.
 

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I didn't take the class on bearing failures, but the closest thing I found from googling bearing failures is referred to as false brinneling.

Caused by vibrations when the bearing is not rotating. One site stated it used to be common problem on cars shipped by rail.

Begs the question whether the PO was a trailer and ride type.

http://www.tec.nsk.com/Troubleshooting/DamageTypesAndCauses/BigPic.html?pic=phbp1201a

http://www.tec.nsk.com/Troubleshooting.asp?menu=2,0,0,0&PageID=/DamageTypesAndCauses/FalseBrinelling.html
 

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Discussion Starter #14
This is interesting too.
Consider the bike on its side stand, on a trailer, pounding along for hundreds of miles. Could such asymmetric bearing damage be caused by that kind of trailer ride?
Seems reasonable to me.
Having removed and installed many of this bearings, I can see how someone might just press a new bearing onto its seat by using a hydralic press on the outer race causing damage. Or even just hammering on the bearing to get it to seat. That is the most likely explaination to me.
Atraumatic bearing installation and proper preload yields a good final drive.
Installation stress or preload stress both can set the stage for failure.
Lots of riding over potholes or long, hard trailering might cause problems too.

Interesting insights from all who post thoughtful comments.... keep 'em coming.
Thanks,
C.


jrh2020 said:
I didn't take the class on bearing failures, but the closest thing I found from googling bearing failures is referred to as false brinneling.

Caused by vibrations when the bearing is not rotating. One site stated it used to be common problem on cars shipped by rail.

Begs the question whether the PO was a trailer and ride type.

http://www.tec.nsk.com/Troubleshooting/DamageTypesAndCauses/BigPic.html?pic=phbp1201a

http://www.tec.nsk.com/Troubleshooting.asp?menu=2,0,0,0&PageID=/DamageTypesAndCauses/FalseBrinelling.html
 

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Hoping I can shed more light. The PO of this bike was/is a rider - GoldenDragon. Best of my knowledge, he didn't trailer it anywhere.
Could false brinneling occur on a bearing shimmed properly, as should our crown wheel bearings? I'm just trying to think this through, and it seems like there should be enough side pressure, outer to inner race, by the shimming, to prevent the damage. I certainly don't know that though.
I believe that two of us correctly measured the pre-load of the failed bearing, and determined that it was over-shimmed. After seating the new bearing, I found that the pre-load was considerably different (more) than the failed bearing. That was what caused me to wonder if the failed bearing wasn't properly seated on the hub. Guess I should have either photographed the failed bearing, prior to removal, or just sent it to Curtis. My bad.
 

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Also keep in mind with my guess the mechanical dynamics of a radial ball bearing in regards too surface distance differences between inner and outer races ?
The inner race has LESS distance than the outer race having the ball between them be in a slight skid at all times. This skidding is negated by allowing retainer rotation. But it is happening never the less. Stop the rotation of the retainer and the balls will spin greater on the inner race having the shorter distance to make the 360*
Contact angle of the races dictate the outside race having a concave shape contacts each ball with greater area than the convex surface of the inner race. So the outside race is the primary ball driver generally with the inner race absorbing the skid.

We making sense here ?

Scott
 

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Jim, thanks for posting the link. Very interesting reading/pictures.

For most of us non bearing-guru types bearings are the things on your boat trailer that you keep lubed so you aren't left stranded beside the road. There are also a few of them inside components under the hood of your car. Water pump, alternator, etc.

It's comforting to know there are folks on this forum who are smart enough to read the bearing "tea leaves" and theorize as to the cause of failure.

Thanks for being there guys!

Loren

jrh2020 said:
The false brinelling appears to be limited to stationary vibration environments. Found a little more reputable site, page 12 & 13 of the pdf.

http://www.alliedbearings.com/downloads/skf_bearing_failureandcauses.pdf

The cage damage wouldn't appear to fit very well with this theory either.

I'm out of ideas, but the installation stress fits as well.
 

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Discussion Starter #19
jrh2020 said:
The false brinelling appears to be limited to stationary vibration environments. Found a little more reputable site, page 12 & 13 of the pdf.

http://www.alliedbearings.com/downloads/skf_bearing_failureandcauses.pdf

The cage damage wouldn't appear to fit very well with this theory either.

I'm out of ideas, but the installation stress fits as well.
This is a really great link! Thanks.
I think I am seeing primarily two things contributing to the failure of these bearings:
The section on Flaking Caused by Preload fits many of the failed bearings I have seen. The section on Surface Distress also applies because surface distress will occur secondary to excess preload which decreases the lubricant space between the races and the rolling surfaces.
The section on Surface Indentations also makes sense for some bearings I have seen; the one pictured in this thread may be a good example.

Damage to the cage (retainer) is secondary to damage to the races and balls IMO. Improper installation resulting in Surface Indentations and excess preload resulting in Flaking (spalling) are both probable causes of the failed crownwheel bearings we are seeing. Once the defects in the races are established, the balls encounter increasing resistance during rotation under radial load (the weight of the bike, rider, etc.) and the stress builds on the retainer until the retainer fatigues and breaks.

When caught early by the rider sensing roughness, I have seen damaged races but with the retainer intact. Others, such as the bearing pictured in this thread, had damaged races, and early retainer failure. Note that in the case of the bearing pictured in this thread the broken retainer wasn't identified until the drive was opened and the bearing viewed. The most common stage of bearing failure detection is when shards from the broken retainer tear up the nearby oil seal and the lube leaks out.

While potholes, improper lubrication, damage due to extended trailering are all possible causes, I think that the rash of crownwheel bearings seen in the early years of the K1200LT are the result of improper bearing setup and/or improper installation techniques. I think the data available now pretty well supports this theory.
Thanks to all who have contributed thoughts, suggestions, experiences, and bearings to this inquiry.
Cheers!
 

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fpmlt said:
Hoping I can shed more light. The PO of this bike was/is a rider - GoldenDragon. Best of my knowledge, he didn't trailer it anywhere.
.
Keep in mind all these bikes are shipped from der fatherland. By truck, by ship, possibly by train as well.
 
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