Engineers, look at this bearing please - BMW Luxury Touring Community
 
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post #1 of 48 Old May 20th, 2010, 5:56 pm Thread Starter
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Engineers, look at this bearing please

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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post #2 of 48 Old May 20th, 2010, 6:19 pm
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Re: Engineers, look at this bearing please

Quote:
Originally Posted by CharlieVT
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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post #3 of 48 Old May 20th, 2010, 6:21 pm
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Re: Engineers, look at this bearing please

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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post #4 of 48 Old May 20th, 2010, 6:22 pm
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Re: Engineers, look at this bearing please

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

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post #5 of 48 Old May 20th, 2010, 6:46 pm Thread Starter
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Re: Engineers, look at this bearing please

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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post #6 of 48 Old May 20th, 2010, 6:50 pm
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Re: Engineers, look at this bearing please

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

Quote:
Originally Posted by CharlieVT
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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Our "semi" quiet riot
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post #7 of 48 Old May 20th, 2010, 6:52 pm Thread Starter
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Re: Engineers, look at this bearing please

Quote:
Originally Posted by fpmlt
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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post #8 of 48 Old May 20th, 2010, 7:05 pm Thread Starter
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Re: Engineers, look at this bearing please

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.

Quote:
Originally Posted by motorhead
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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post #9 of 48 Old May 20th, 2010, 7:42 pm
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Re: Engineers, look at this bearing please

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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post #10 of 48 Old May 20th, 2010, 8:10 pm Thread Starter
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Re: Engineers, look at this bearing please

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.....



Quote:
Originally Posted by fpmlt
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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post #11 of 48 Old May 20th, 2010, 8:13 pm
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Re: Engineers, look at this bearing please

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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post #12 of 48 Old May 20th, 2010, 8:16 pm Thread Starter
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Re: Engineers, look at this bearing please

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


Quote:
Originally Posted by dshealey
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.

Last edited by CharlieVT; May 20th, 2010 at 8:24 pm.
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post #13 of 48 Old May 20th, 2010, 8:21 pm
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Re: Engineers, look at this bearing please

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/Troubleshooti...?pic=phbp1201a

http://www.tec.nsk.com/Troubleshooti...rinelling.html

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post #14 of 48 Old May 20th, 2010, 8:42 pm Thread Starter
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Re: Engineers, look at this bearing please

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.


Quote:
Originally Posted by jrh2020
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/Troubleshooti...?pic=phbp1201a

http://www.tec.nsk.com/Troubleshooti...rinelling.html
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post #15 of 48 Old May 20th, 2010, 9:00 pm
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Re: Engineers, look at this bearing please

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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post #16 of 48 Old May 20th, 2010, 9:43 pm
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Re: Engineers, look at this bearing please

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/downlo...eandcauses.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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post #17 of 48 Old May 21st, 2010, 12:52 am
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Re: Engineers, look at this bearing please

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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post #18 of 48 Old May 21st, 2010, 2:10 am
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Re: Engineers, look at this bearing please

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

Quote:
Originally Posted by jrh2020
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/downlo...eandcauses.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.

WAK1200LT
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post #19 of 48 Old May 21st, 2010, 8:02 am Thread Starter
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Re: Engineers, look at this bearing please

Quote:
Originally Posted by jrh2020
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/downlo...eandcauses.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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post #20 of 48 Old May 21st, 2010, 9:29 am
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Re: Engineers, look at this bearing please

Quote:
Originally Posted by fpmlt
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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post #21 of 48 Old May 21st, 2010, 9:43 am
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Re: Engineers, look at this bearing please

That's a good point, one I hadn't considered, but in this case, this is a replacement bearing, with the FD being rebuilt by a dealer. I'm convinced that this failure is completely due to improper install and shim.

Curtis, you mentioned " 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." I'm taking a lot of heat from my riding buddies, in that they believe my riding style may have contributed to this failure. They point out that I've drug through the skid plate, center stand, and the fairings on both sides. Would you think that could be a contributing factor? Seems like there would be an increased side load, like over shimming, during radical lean. Just wondering, but on the other hand, I ain't gonna change the way I ride.
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post #22 of 48 Old May 21st, 2010, 9:45 am Thread Starter
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Re: Engineers, look at this bearing please

Quote:
Originally Posted by dukey33
Keep in mind all these bikes are shipped from der fatherland. By truck, by ship, possibly by train as well.
Shipped, unassembled, in crates. Pretty sure that the bike's weight is not on the suspension, wheels, or bearings during shipping.
Interesting thought though.
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post #23 of 48 Old Jun 12th, 2010, 11:37 pm
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Re: Engineers, look at this bearing please

Quote:
Originally Posted by motorhead
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
Hi!

I am afraid that you had just gotten yourself a little confused here. Let me assure you that, in operations, there are no skidding involved. In a so-called frictionless bearing (rollers, balls, or needle rollers), skidding is very bad since it will cause serious wear and breakdown of the bearings.

I can see what you are thinking though! Now, if you will just imagine that the outer race is fixed (to the FD housing, in this case), and as you rotate the inner race (the wheel axle assembly), you will observe that while you turn the inner race in one direction, the whole ball assembly (all the balls and the retainer) will be turning in the opposite direction, at a different speed, due to the balls' rolling action!

You should note also that the bearing's ball retainer does absolutely nothing, once the bearing is installed (assuming that it is installed in the proper manner). The retainer is used to keep the balls spaced at the proper intervals around the races, while the bearing still have clearances......that is, before it is installed. Once installed, all of the balls are in firm contact with both races, and will roll without any slippage. The retainer, at this point, is dragged around for the ride, so to say.

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post #24 of 48 Old Jun 12th, 2010, 11:49 pm
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Re: Engineers, look at this bearing please

Curtis,

I had just caught up with this thread!

It is my opinion that the score marks in your photo came about, pretty much as you had surmised, from the improper installation of the bearing. As you had noted, the bearing was probably pressed on with pressure on the outer race, which is a big no-no!!!

My reasoning is this. First, a score marks like those in the photo are created by two surfaces sliding relative to one another, in the direction of the score. Second, when the bearing is fully installed, the balls are in very firm contact with both races (with some predetermined radial pre-load applied), and therefore the bearing assembly will be very rigid. Therefore, in the assembled condition, the balls could not move against the race to make the score lines, especially in that direction! Which means that the scoring was done while the balls are still loose between the races, and therefore leads to the conclusion that it was done as the bearing was being pressed onto the bearing seat.

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post #25 of 48 Old Jun 13th, 2010, 5:55 am Thread Starter
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Re: Engineers, look at this bearing please

Thanks for the analysis!
Pretty much what I had assumed, that someone had hammered the bearing.
I don't believe that this is the case with all the failed bearings I have seen, but this one was kind of unique.
However, if this bearing had continued to be run, I suspect that the axial pitting of the races may have become obliterated, and then the appearance of more severe radial pitting would have developed; radial pitting is the most common finding in the failed bearings I have seen.
Thanks again,


Quote:
Originally Posted by PadG
Curtis,

I had just caught up with this thread!

It is my opinion that the score marks in your photo came about, pretty much as you had surmised, from the improper installation of the bearing. As you had noted, the bearing was probably pressed on with pressure on the outer race, which is a big no-no!!!

My reasoning is this. First, a score marks like those in the photo are created by two surfaces sliding relative to one another, in the direction of the score. Second, when the bearing is fully installed, the balls are in very firm contact with both races (with some predetermined radial pre-load applied), and therefore the bearing assembly will be very rigid. Therefore, in the assembled condition, the balls could not move against the race to make the score lines, especially in that direction! Which means that the scoring was done while the balls are still loose between the races, and therefore leads to the conclusion that it was done as the bearing was being pressed onto the bearing seat.
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post #26 of 48 Old Jun 13th, 2010, 7:43 am
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Re: Engineers, look at this bearing please

Quote:
Originally Posted by PadG
Hi!

I am afraid that you had just gotten yourself a little confused here. Let me assure you that, in operations, there are no skidding involved. In a so-called frictionless bearing (rollers, balls, or needle rollers), skidding is very bad since it will cause serious wear and breakdown of the bearings.
I agree, there is NO skidding in a properly assembled and loaded ball bearing. Would not last long if there was.
Quote:

I can see what you are thinking though! Now, if you will just imagine that the outer race is fixed (to the FD housing, in this case), and as you rotate the inner race (the wheel axle assembly), you will observe that while you turn the inner race in one direction, the whole ball assembly (all the balls and the retainer) will be turning in the opposite direction, at a different speed, due to the balls' rolling action!
Different speed (slower), but SAME DIRECTION.
Quote:
You should note also that the bearing's ball retainer does absolutely nothing, once the bearing is installed (assuming that it is installed in the proper manner). The retainer is used to keep the balls spaced at the proper intervals around the races, while the bearing still have clearances......that is, before it is installed. Once installed, all of the balls are in firm contact with both races, and will roll without any slippage. The retainer, at this point, is dragged around for the ride, so to say.
Correct.

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post #27 of 48 Old Jun 13th, 2010, 9:21 am
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Re: Engineers, look at this bearing please

Then why isn't there a bearing failure with a retainer in tact? Many bearing failures are noticed because the seal is cut and fluid runs out. My failures (2) never cut the seal but the retainer was destroyed. So, is it a bearing failure or a retainer failure? I'm no engineer but I did stay at a Holiday Inn Express once...........

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post #28 of 48 Old Jun 13th, 2010, 9:28 am Thread Starter
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Re: Engineers, look at this bearing please

Quote:
Originally Posted by rattler50
Then why isn't there a bearing failure with a retainer in tact? Many bearing failures are noticed because the seal is cut and fluid runs out. My failures (2) never cut the seal but the retainer was destroyed. So, is it a bearing failure or a retainer failure? I'm no engineer but I did stay at a Holiday Inn Express once...........
There are failures with the retainer intact. I've posted examples of this with pics in the past.

I now have a few examples of failed bearings where the retainer was intact. These are cases where the rider stopped riding because roughness was felt and/or metal was seen on the drain plug magnet. In these select cases, the seal was intact and there was no leak of lube.

I was fortunate to have these drives sent to me so I could cut open the bearings and inspect. In all of these select cases I found spalling of the races to some degree, but the retainers were intact. The metal on the magnet was from the degrading races and/or balls. The roughness felt during rotation was clearly from the spalling.

My conclusion is that if these riders had continued to ride they would soon have experienced retainer failure and seal failure.
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post #29 of 48 Old Jun 13th, 2010, 11:55 am
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Re: Engineers, look at this bearing please

Is there any chance that the markings are from harsh removal of the bearing, rather than a harsh installation?
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Re: Engineers, look at this bearing please

Quote:
Originally Posted by fpmlt
Is there any chance that the markings are from harsh removal of the bearing, rather than a harsh installation?
Well yes possibly, but this bearing had a history prior to removal. Roughness was noted prior to removal of the bearing, and the retainer was broken prior to removal of the bearing. Whatever was going on, it wasn't just about the removal. From my original post in this thread:

"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."
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post #31 of 48 Old Jun 13th, 2010, 10:27 pm
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Re: Engineers, look at this bearing please

Quote:
Originally Posted by PadG
Hi!

I am afraid that you had just gotten yourself a little confused here. Let me assure you that, in operations, there are no skidding involved. In a so-called frictionless bearing (rollers, balls, or needle rollers), skidding is very bad since it will cause serious wear and breakdown of the bearings.
Disclaimer: I am not a bearing designer.

Having said that, I don't see how the above can be true for a ball bearing in a race that has more than a point contact with the balls. If both inner and outer races were just cylinders, then I can see how no skidding occurs. However, most ball bearing races have a semicircular channel with some depth. I believe that the farther around the ball this channel extends, the greater will the degree of slip.

As an engineer, I often look at the limit cases to see what happens and then you can often (but not always!) interpolate to find intermediate cases. One limit is the case above where the races are complete cylindrical and the balls contact at a "point." I say point in quotes as this is an idealization that doesn't actually exist once a load is applied some indentation occurs and the point becomes an area.

The other limit is where the races have depth equal to the ball radius. The inner and outer races now completely encircle the balls and just touch each other as well. When the bearing is rotated, the inner and out races will move past each other at the center of rotation of the balls. So at the center of rotation, the "side" of the ball will be moving at a velocity that is the average of the velocity of the inner and outer races. If you move an infintesimal distance away from the center of the ball rotation and look at that point, it will make a small radius orbit around the center of rotation of the ball and thus will be touching the inner radius for half of a ball rotatation and touching the outer race for the other half of the rotation. Since the speed of the ball and the faces are quite different, I believe this point on the ball will skid against each race at a velocity equal to difference between the velocity of that ball and that of the inner and outer races.

As you move away from the center of rotation of the ball down to the "bottom" of the face, this skid velocity will approach zero as the bottom of the race is approached. I therefore believe that a substantial part of each ball is skidding against the race and only the part at the very bottom of the race groove as a truly zero relative velocity. This is why bearings need to be lubricated. If no skidding occured, there would be no need for lubricant.

If anyone sees an error in my logic, please point it out.

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post #32 of 48 Old Jun 14th, 2010, 12:23 am
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Re: Engineers, look at this bearing please

In adding to this ... if you placed a ball bearing between 2 flat surfaces with race grooves and drew them in opposite dirrection the ball would spin yet stay stationary as the surface distance of each is equal. If a radial ball bearing had equal surface distance on both inner and outer races, it's balls too would stay in a fixed position .... would they not ?



Quote:
Originally Posted by Voyager
Disclaimer: I am not a bearing designer.

Having said that, I don't see how the above can be true for a ball bearing in a race that has more than a point contact with the balls. If both inner and outer races were just cylinders, then I can see how no skidding occurs. However, most ball bearing races have a semicircular channel with some depth. I believe that the farther around the ball this channel extends, the greater will the degree of slip.

As an engineer, I often look at the limit cases to see what happens and then you can often (but not always!) interpolate to find intermediate cases. One limit is the case above where the races are complete cylindrical and the balls contact at a "point." I say point in quotes as this is an idealization that doesn't actually exist once a load is applied some indentation occurs and the point becomes an area.

The other limit is where the races have depth equal to the ball radius. The inner and outer races now completely encircle the balls and just touch each other as well. When the bearing is rotated, the inner and out races will move past each other at the center of rotation of the balls. So at the center of rotation, the "side" of the ball will be moving at a velocity that is the average of the velocity of the inner and outer races. If you move an infintesimal distance away from the center of the ball rotation and look at that point, it will make a small radius orbit around the center of rotation of the ball and thus will be touching the inner radius for half of a ball rotatation and touching the outer race for the other half of the rotation. Since the speed of the ball and the faces are quite different, I believe this point on the ball will skid against each race at a velocity equal to difference between the velocity of that ball and that of the inner and outer races.

As you move away from the center of rotation of the ball down to the "bottom" of the face, this skid velocity will approach zero as the bottom of the race is approached. I therefore believe that a substantial part of each ball is skidding against the race and only the part at the very bottom of the race groove as a truly zero relative velocity. This is why bearings need to be lubricated. If no skidding occured, there would be no need for lubricant.

If anyone sees an error in my logic, please point it out.

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post #33 of 48 Old Jun 14th, 2010, 12:31 am
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Re: Engineers, look at this bearing please

Most of my thoughts have been covered by others.

Yes the races could look like fretting damage from extensive static loading from shipping damage. That is a real consideration for wheel bearings in the automotive industry.

And it could be installation and removal damage. The correct term is brinneling, which is plastic deformation caused by one helluva load. I gather the indentations are all around the perimeter of the outer race, and there are corresponding marks on the inner race?

Chunks missing from the races and/or the balls? that's fatigue induced damage from too much load or too many revolutions under high load.

The cage disintegrated? If so, pieces of the cage probably were fed thru the rolling ball-cage interface which can generate enormous loads within the bearing that could brinnel things - but the markings won't be the same all around the races from this sort of trauma. Unfortunately when a roller or ball bearing disintegrates, the pieces will do so much damage that the source of the initial damage is hard or even impossible to predict.

My first guess is damage from poor assembly procedures.

Isn't this an aluminum shaft? If so, heating the assembly will just make the bearing even harder to remove. Remember - it is .001 inch per inch difference for each 160 degF temperature rise for an aluminum-steel interface. Assuming it is aluminum, chilling the whole thing in LN2 would make it fall apart by itself.

OBTW - yes balls have to skid on a race - especially when a finite contact patch is needed to carry the load.

Gotta think some more on this one..............
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post #34 of 48 Old Jun 14th, 2010, 12:52 am
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Re: Engineers, look at this bearing please

I love this stuff !! ..... nothing is face value because nothing seldom is what it appears.

Ok ... think cap on boyz
Lets step back to the basic mechanical dynamics of the bearing application we are talking about ... a axial preloaded symmetrical race bearing having equal race depth on inner and outer race ....

Now this bearing is axially loaded placing SIDE thrust upon it. now rather than balls being in contact with the valley of the race groove as it would when dealing with radial loading, the contact point of balls are up on the side of the race grooves being opposite on each race.
Now the balls are by virtue of being in a lateral compressed space between races are forced to spin damn near 90* to the races rotation. The tilt of the spin being relative to the difference in balls diameter and how close the edge of each race is to the balls dimensional center line. In other words the balls are very close to spinning like a top on a table top as the table is sliding beneath it.

This is physics and don't think when we remove what we think we know and apply what the mechanical physics are this can be disagreed with ?

Now this same bearing is also subjected too radial loading at the same time so those forces are trying to force the balls into the valley of each raceway and roll the balls in the same direction as races move.
Yea you get a better idea of the shear mechanical load placed on the ball itself, the skidding, the top spin effect all while trying to stay intact without failure.

Radial ball bearings that are designed for heavy axial loading have offset height race shoulders and NEED preload to remove wiggle radially.
In such an application as described above the balls are made to spin like a top having the thrust surface of each race near the balls center line axially. This type bearing not so different than what we use except the bearing requires a precise preload to function correctly. Typically these type bearings are used on lathe headstocks, milling machine spindles etc.

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post #35 of 48 Old Jun 14th, 2010, 4:48 pm
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Re: Engineers, look at this bearing please

I agree the contact point(s) on the races moves around the race grooves under combined loading, and that this could even cause differential speed of the balls as they chase each other around constrained by the cage. Of course this means the cage has to restore each ball to its average position every revolution of the cage. This is probably what causes cage fatigue.

This bearing sees thrust (from the opposing tapered roller bearing), radial (the bike weight), pitch moment (from bike banking though it is minor), and yaw moment (from the thrust faces of the gears) loading. The contact points of the balls is moving around the grooves in a very complex manner, and as a result the cage could experience some substantial fatigue loading.

I'd hate to have to calculate/analyze the projected life of this bearing.

Could someone confirm if the hub is aluminum? I've never had one apart.
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post #36 of 48 Old Jun 14th, 2010, 5:55 pm Thread Starter
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Re: Engineers, look at this bearing please

Quote:
Originally Posted by niel_petersen
I agree the contact point(s) on the races moves around the race grooves under combined loading, and that this could even cause differential speed of the balls as they chase each other around constrained by the cage. Of course this means the cage has to restore each ball to its average position every revolution of the cage. This is probably what causes cage fatigue.

This bearing sees thrust (from the opposing tapered roller bearing), radial (the bike weight), pitch moment (from bike banking though it is minor), and yaw moment (from the thrust faces of the gears) loading. The contact points of the balls is moving around the grooves in a very complex manner, and as a result the cage could experience some substantial fatigue loading.

I'd hate to have to calculate/analyze the projected life of this bearing.

Could someone confirm if the hub is aluminum? I've never had one apart.
The "hub" is made of both carbon steel and aluminum.

I call this assembly a "hub" since it is the component that the rear wheel bolts to.
BMW calls the part the "crowngear".
http://www.maxbmwmotorcycles.com/fic...aspx?vid=51717
Go to item #33 - Rear axle and suspension.

The "hub" consists of two parts assembled by BMW and only available as a component which BMW parts lists call the crowngear. Actually, you can't even buy the crowngear, it comes as a crowngear and pininon gear set which the parts list calls a "differential gear set". 'Course we know it isn't a differential

So the "hub" or "crowngear" is made up of a carbon steel component which is the gear itself and the hub that the wheel bolts to. There is an aluminum component to the crowngear assembly which has the seat for the tapered roller bearing milled into it. These two components are press fitted together to form the "crowngear" assembly.
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post #37 of 48 Old Jun 14th, 2010, 5:56 pm
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Re: Engineers, look at this bearing please

You are making the assumption that the balls contact the races over a large area of the curves. That is not the case. Deep groove bearing races are ground in a "Gothic Curve" shape, not a perfect radius. Therefore the balls only contact at a point on the race. The contact points move up or down the race surfaces depending on the forces applied, radial vs axial, but in any case the points of contact are diametrically opposed across the ball, so that the speed of rotation remains relative to the distance from center of axle, so that the balls do not have to skid. Any skidding of the balls on the races will damage a bearing in short order. Many decades of design have gone into ball bearings to insure no skidding.

If the load is perfectly radial (rare) then the balls touch two points on each race, the points on each race being in the same plane relative to the axle rotation.

Quote:
Originally Posted by niel_petersen
Most of my thoughts have been covered by others.

Yes the races could look like fretting damage from extensive static loading from shipping damage. That is a real consideration for wheel bearings in the automotive industry.

And it could be installation and removal damage. The correct term is brinneling, which is plastic deformation caused by one helluva load. I gather the indentations are all around the perimeter of the outer race, and there are corresponding marks on the inner race?

Chunks missing from the races and/or the balls? that's fatigue induced damage from too much load or too many revolutions under high load.

The cage disintegrated? If so, pieces of the cage probably were fed thru the rolling ball-cage interface which can generate enormous loads within the bearing that could brinnel things - but the markings won't be the same all around the races from this sort of trauma. Unfortunately when a roller or ball bearing disintegrates, the pieces will do so much damage that the source of the initial damage is hard or even impossible to predict.

My first guess is damage from poor assembly procedures.

Isn't this an aluminum shaft? If so, heating the assembly will just make the bearing even harder to remove. Remember - it is .001 inch per inch difference for each 160 degF temperature rise for an aluminum-steel interface. Assuming it is aluminum, chilling the whole thing in LN2 would make it fall apart by itself.

OBTW - yes balls have to skid on a race - especially when a finite contact patch is needed to carry the load.

Gotta think some more on this one..............

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post #38 of 48 Old Jun 14th, 2010, 10:07 pm
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Re: Engineers, look at this bearing please

Quote:
Originally Posted by dshealey
You are making the assumption that the balls contact the races over a large area of the curves. That is not the case.
Your steels must have a lot higher modulus than the ones I worked with...........
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post #39 of 48 Old Jun 14th, 2010, 10:23 pm
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Re: Engineers, look at this bearing please

Quote:
Originally Posted by niel_petersen
Your steels must have a lot higher modulus than the ones I worked with...........
Or more lightly loaded bearings. :-)

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post #40 of 48 Old Jun 14th, 2010, 10:29 pm
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Re: Engineers, look at this bearing please

This sure looks like the balls were rolling in one place..

I have several thoughts why...

Before "installing" a bearing I think there should be a way to "run in" the bearing to ensure the bearing is working properly... Check for smooth movement.. check for harmonics/vibrations, etc.

Once "installed" in the drive, the harmonics should again be retested..

During install, I imagine this causes some distortion of the outer and inner race...

It only requires one of the ball bearings to fail or be out of round for this kind of failure to occur..... testing for harmonics/smooth movement/rolling are key..

If anyone has ever worked on turbines, they can describe the testing of the bearings..

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post #41 of 48 Old Jun 15th, 2010, 7:18 am Thread Starter
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Re: Engineers, look at this bearing please

Thanks Gents.

When I first posted the start to this thread, I was curious about the unusual pattern of pitting on the races.

Having made a hobby of trying to understand what is happening that leads to these Final Drive failures, all I think I know comes from the posts of the folks on this board who have a mechanical engineering education and who have been willing to share information and insights. Thanks to you all, you guys know who you are.

It is kinda fun to get engineers "spun up" and watch the discussion.

(I realize not all "engineers" know bearings, engineering disciplines are pretty focused. It is easy to speculate on how things work outside the areas of our own expertise, and "we don't know what we don't know". Sorting speculation and theory from data based knowledge is part of the process, and I appreciate all thoughtful posts in response to my query. On a person note, son just graduated RPI in Materials Science. Smart boy, but I don't think he knows anything about bearings )
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post #42 of 48 Old Jun 15th, 2010, 3:07 pm
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Re: Engineers, look at this bearing please

Quote:
Originally Posted by CharlieVT
son just graduated RPI in Materials Science. Smart boy, but I don't think he knows anything about bearings )
Rensselaer Polytechnic Institute? Congratulations! He'll be a good crap detector, and that's all you need.
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post #43 of 48 Old Jun 15th, 2010, 3:39 pm Thread Starter
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Re: Engineers, look at this bearing please

Quote:
Originally Posted by niel_petersen
Rensselaer Polytechnic Institute? Congratulations! He'll be a good crap detector, and that's all you need.
Yup, that's the place. My last tuition check has been written! Now I can concentrate on paying for a nice long ride to Alaska!
(Spare crownwheel bearing in the side case).

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post #44 of 48 Old Jun 15th, 2010, 4:33 pm
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Re: Engineers, look at this bearing please

Quote:
Originally Posted by CharlieVT
Thanks Gents.

When I first posted the start to this thread, I was curious about the unusual pattern of pitting on the races.

Having made a hobby of trying to understand what is happening that leads to these Final Drive failures, all I think I know comes from the posts of the folks on this board who have a mechanical engineering education and who have been willing to share information and insights. Thanks to you all, you guys know who you are.

It is kinda fun to get engineers "spun up" and watch the discussion.

(I realize not all "engineers" know bearings, engineering disciplines are pretty focused. It is easy to speculate on how things work outside the areas of our own expertise, and "we don't know what we don't know". Sorting speculation and theory from data based knowledge is part of the process, and I appreciate all thoughtful posts in response to my query. On a person note, son just graduated RPI in Materials Science. Smart boy, but I don't think he knows anything about bearings )
YOU MUST BE VERY PROUD
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post #45 of 48 Old Jun 15th, 2010, 7:39 pm
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Re: Engineers, look at this bearing please

Curtis
Starting engineer threads could get you banned - just like Ams*** oil threads!!!!!!
I've been away and just logged in - so will add my $0.02 (Can) engineering perspective
- sure looks like assembly/disassembly marks to me.
- Extended vibration can cause marks like this - but not in this case
- the balls in this "single row deep groove" ball bearing (or others) dont skid in normal operation. Debris caught in the races can cause skidding - followed quickly by failure
- the bikes are shipped on their wheel from the factory and tied down in a steel frame. This is a photo of my bike when it arrived at the dealer.

based on all your hard work and analysis of failures- I still agree with you - it is primarily a preload issue.
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2015 K1600GTL
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post #46 of 48 Old Jun 19th, 2010, 9:16 am
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Re: Engineers, look at this bearing please

Quote:
Originally Posted by rattler50
Then why isn't there a bearing failure with a retainer in tact? Many bearing failures are noticed because the seal is cut and fluid runs out. My failures (2) never cut the seal but the retainer was destroyed. So, is it a bearing failure or a retainer failure? I'm no engineer but I did stay at a Holiday Inn Express once...........
Destroyed or damaged retainer is only a "symptom" of catastrophic bearing failures. As Curtis had pointed out, there are failures with undamaged retainer, which indicates that the bearing failure was caught before things got really bad.

When a ball, or balls, starts to self-destruct, it may start to skid and therefore runs into the retainer being dragged along at normal speed by the rest of the balls, and therefore exert some force on the retainer. The other thing that happens is that fragments of the failed bearings or parts of the damaged retainer, gets caught up in the assembly and cause damages, or further damages to the retainer.

Pad. Gajajiva
Solon, OH, USA

2015 R1200RT (San Marino Blue Met.)
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Once Upon a Time........
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1960 Triumph Bonneville (T120)
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post #47 of 48 Old Jun 19th, 2010, 9:20 am
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Re: Engineers, look at this bearing please

Quote:
Originally Posted by fpmlt
Is there any chance that the markings are from harsh removal of the bearing, rather than a harsh installation?
Only a very slight one, or none, in my opinion! Two things need to happen to create those marks. First, the balls must be loose with respect to the races, and second, a good amount of force needs to be applied when the balls were loose. In removing, even improperly, the balls are tight against both races until the bearing is off its "seat", at which time the pulling force would have been very low or minimal!

Pad. Gajajiva
Solon, OH, USA

2015 R1200RT (San Marino Blue Met.)
2014 R1200RT (Quartz Metallic Blue - Returned to BMW)
2007 R1200RT (Sold!)


Once Upon a Time........
1963 Norton Dominator 650 SS
1960 Triumph Bonneville (T120)
1960 Triumph Thunderbird (6T)
1952 Triumph Thunderbird (6T)
1932 Triumph 500
1952 BSA Goldstar
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post #48 of 48 Old Jun 19th, 2010, 9:28 am
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Re: Engineers, look at this bearing please

Quote:
Originally Posted by Voyager
Disclaimer: I am not a bearing designer.

Having said that, I don't see how the above can be true for a ball bearing in a race that has more than a point contact with the balls. If both inner and outer races were just cylinders, then I can see how no skidding occurs. However, most ball bearing races have a semicircular channel with some depth. I believe that the farther around the ball this channel extends, the greater will the degree of slip.

As an engineer, I often look at the limit cases to see what happens and then you can often (but not always!) interpolate to find intermediate cases. One limit is the case above where the races are complete cylindrical and the balls contact at a "point." I say point in quotes as this is an idealization that doesn't actually exist once a load is applied some indentation occurs and the point becomes an area.

The other limit is where the races have depth equal to the ball radius. The inner and outer races now completely encircle the balls and just touch each other as well. When the bearing is rotated, the inner and out races will move past each other at the center of rotation of the balls. So at the center of rotation, the "side" of the ball will be moving at a velocity that is the average of the velocity of the inner and outer races. If you move an infintesimal distance away from the center of the ball rotation and look at that point, it will make a small radius orbit around the center of rotation of the ball and thus will be touching the inner radius for half of a ball rotatation and touching the outer race for the other half of the rotation. Since the speed of the ball and the faces are quite different, I believe this point on the ball will skid against each race at a velocity equal to difference between the velocity of that ball and that of the inner and outer races.

As you move away from the center of rotation of the ball down to the "bottom" of the face, this skid velocity will approach zero as the bottom of the race is approached. I therefore believe that a substantial part of each ball is skidding against the race and only the part at the very bottom of the race groove as a truly zero relative velocity. This is why bearings need to be lubricated. If no skidding occured, there would be no need for lubricant.

If anyone sees an error in my logic, please point it out.
I won't respond to every details. Don't want to spend too much time on this. I suggest that you look at the lay-out for an "Epicyclic Gear system" as a parallel example. For the lay person, this is what is sometimes called the planetary gear system. This will show very clearly (since they are gears) that such lay out will never slip!

BTW, you should think again about what role lubricants plays!

Pad. Gajajiva
Solon, OH, USA

2015 R1200RT (San Marino Blue Met.)
2014 R1200RT (Quartz Metallic Blue - Returned to BMW)
2007 R1200RT (Sold!)


Once Upon a Time........
1963 Norton Dominator 650 SS
1960 Triumph Bonneville (T120)
1960 Triumph Thunderbird (6T)
1952 Triumph Thunderbird (6T)
1932 Triumph 500
1952 BSA Goldstar
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