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post #1 of 38 Old Mar 20th, 2010, 1:40 pm Thread Starter
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JD's bearing pics

Drive history: was at the dealer for FD oil change, reportedly oil was free of metal at that time. 300 miles later rider reported roughness in the ride.

Pics are of the drain plug viewed from inside the drive.
Inner race, outer race (which has been cut in two for disassembly), a pic of the ball bearings.
The ball retainer was intact and all balls in place. So all that metal is of ball bearings and races, no shards of retainer. Although, I'm sure the retainer would have disintegrated in a few more miles had the bike been ridden further.
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post #2 of 38 Old Mar 24th, 2010, 3:28 pm Thread Starter
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M.T.'s bearing pic

retainer pretty well torn up on this one.
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post #3 of 38 Old Mar 24th, 2010, 5:53 pm
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Re: JD's bearing pics

Perhaps I missed something, but is the second post a picture of the same bearing? Thought the first post said that the bearing retainer was in tact.

If the retainer was in tact, what's your best guess as to the cause of the damage to the balls and races?
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post #4 of 38 Old Mar 24th, 2010, 6:37 pm
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Re: JD's bearing pics

Quote:
Originally Posted by CharlieVT
Drive history: was at the dealer for FD oil change, reportedly oil was free of metal at that time. 300 miles later rider reported roughness in the ride.

Pics are of the drain plug viewed from inside the drive.
Inner race, outer race (which has been cut in two for disassembly), a pic of the ball bearings.
The ball retainer was intact and all balls in place. So all that metal is of ball bearings and races, no shards of retainer. Although, I'm sure the retainer would have disintegrated in a few more miles had the bike been ridden further.
From a happy FD to a crappy FD in only 300 miles. So if I change my FD fluid every 6000 miles (which I do) I've got a 1 in 20 chance of catching a premature failure in my garage during service. If I did 12000 mile changes my odds would plunge to 1 in 40. FD oil is pretty cheap. So I guess when I changed my FD oil last weekend @ 24000 miles and the plug was clean it shouldn't have given me too much comfort. Oh well what the heck, ride it till it breaks then fix it or shoot it. lol

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post #5 of 38 Old Mar 24th, 2010, 6:53 pm Thread Starter
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Talking Re: JD's bearing pics

Quote:
Originally Posted by fpmlt
Perhaps I missed something, but is the second post a picture of the same bearing? Thought the first post said that the bearing retainer was in tact.

If the retainer was in tact, what's your best guess as to the cause of the damage to the balls and races?
Sorry for the confusion. I am rebuilding a couple of final drives. I wanted to send each owner a pic of their respective bearings but couldn't attach the pic to a private msg, so I put 'em in the chat board and PM'd the guys to tell them where they could see the pics.
Then some forum guy moved the thread here I guess.
I am not trying to start another FD thread. Use the search function, there's as many FD threads as there are oil and tire threads.

So to clarify, those bearings are from two different drives, the first post belonging to John D. the second post is from Mitch T.'s final drive.
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post #6 of 38 Old Mar 24th, 2010, 7:17 pm
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Re: JD's bearing pics

Thanks, that clears up part one. Any thoughts on why the first posted bearings failed? I'm no expert, but it looks like a lubrication problem/failure. Would like to hear your thoughts.
Thanks,
Frank
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post #7 of 38 Old Mar 24th, 2010, 8:09 pm
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Re: JD's bearing pics

Quote:
Originally Posted by LARK
From a happy FD to a crappy FD in only 300 miles. So if I change my FD fluid every 6000 miles (which I do) I've got a 1 in 20 chance of catching a premature failure in my garage during service. If I did 12000 mile changes my odds would plunge to 1 in 40. FD oil is pretty cheap. So I guess when I changed my FD oil last weekend @ 24000 miles and the plug was clean it shouldn't have given me too much comfort. Oh well what the heck, ride it till it breaks then fix it or shoot it. lol
There is a really good chance you won't see a failure like this. Most of the documented 05+ failures were the smaller taper bearing spinning on the aluminum cone. Not the big bearing that the early bikes suffered with.

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post #8 of 38 Old Mar 24th, 2010, 8:22 pm Thread Starter
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Re: JD's bearing pics

Quote:
Originally Posted by fpmlt
Thanks, that clears up part one. Any thoughts on why the first posted bearings failed? I'm no expert, but it looks like a lubrication problem/failure. Would like to hear your thoughts.
Thanks,
Frank
Frank,
No one knows for sure. BMW probably has a pretty good idea but they aren't sharing their conclusions.
Lots of possible factors, improper lube, microstresses to bearing during install, improper/inadequate design all have been proposed as causes. I have rebuilt quite a few drives where the crown wheel bearing failed and in every case I used thinner shimming for preload than was originally in there. (The value of that observation can be argued but I don't want to get too arcane here.) Initially I wasn't documenting what orignal shims were, but my data collection and measurement techniques have become better with time. In short, I suspect excessive preload may be a significant factor in failure of these drives.
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post #9 of 38 Old Mar 24th, 2010, 8:43 pm
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Re: JD's bearing pics

OK, I just thought that because of the retainer ring being in tact, this might be something out of the ordinary. I'm guessing, then, that this retaining ring would likely have failed in short order.
Does seeing this cause you to make any other conclusions? Does it appear that this is the beginning of the failure, with the retaining ring failing shortly after this?
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post #10 of 38 Old Mar 25th, 2010, 6:40 am Thread Starter
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Re: JD's bearing pics

Quote:
Originally Posted by fpmlt
OK, I just thought that because of the retainer ring being in tact, this might be something out of the ordinary. I'm guessing, then, that this retaining ring would likely have failed in short order.
Does seeing this cause you to make any other conclusions? Does it appear that this is the beginning of the failure, with the retaining ring failing shortly after this?
Uh Oh.... another FD thread, apologies.....

By asking riders the history of the failure and correlating their story with the severity of bearing damage I have come to believe that the retainer fails after the balls and races have degraded. Years ago when these failures were being discussed there was some speculation that the retainer wasn't beefy enough and people went looking for a different bearing with a more robust retainer; I think a more robust retainer wouldn't make much difference. I think that the retainer failing is secondary to spalling and pitting of the races and balls. The damaged balls then stress the retainer which then breaks.
Riders who notice roughness or metal in the oil and stop riding will have a bearing where the balls and races are damaged but the retainer is intact; witness the first bearing posted in this thread.
Riders who continue to ride, not having noticed roughness, or in a desire to get further down the road, will ultimately experience failure of the retainer. Shards of the broken retainer then tear out the main oil seal at the wheel hub and the drive pukes oil all over the rear brake, tire, etc.
In summary, IMO, the process begins with ball and race spalling. From what I have read, and what mechanical engineers have told me, this process is most likely initiatiated by transient stress on the bearing during installation, or long term stress caused by improper axial preload.
Past speculation that the drive was improperly designed for the size of the bike, or that defective componets were the casue of failure is probably wrong IMO. I think that the failures are related to assembly problems, witness the majority of bikes that have gone high mileage without problems. If you want to fault the engineers, you could blame them for designing a drive that is too complicated for the guys on the assembly line to put together consistently.
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post #11 of 38 Old Apr 5th, 2010, 7:53 pm Thread Starter
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Re: M.T.'s bearing pic

Quote:
Originally Posted by CharlieVT
retainer pretty well torn up on this one.
I've become fairly experienced using the FD rebuild method first suggested by DMAN which uses a dial indicator to calculate preload shim thickness. I have wondered how the results of this technique would compare with the technique described in the BMW Service Manual. The BMW technique requires a special tool to stabilize the crownwheel assembly and a depth micrometer used with a machinist's block.
Results obtained using these two different methods have been very close but not exactly the same, most often within 0.05mm of eachother. The measurements between the two techniques are close enough to give me confidence in the methods.

Here are pics of the two techniques:

Comments welcome, especially from the mech. engineers and machinists in the group.
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post #12 of 38 Old Apr 5th, 2010, 9:41 pm
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Re: JD's bearing pics

Charley, I have wondered about the small area that is open inside the final drive, and the very small amount of lubricant that is used. thinking about the drive gearing and the bearing spinning around inside, and given that the drive has air inside it from the fill hole up, is it a possibility that by riding for an extended amount of time, the oil may heat up, and churning air into the mix may starve the bearing for lubricant? I am sure that this problem has been scrutinized from all angles, but at this point there doesn't seem to be any definitive cause..I love the video of the drive rebuild, Thanks for sharing (got cousins and sister in St. Albans and Sheldon springs)

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post #13 of 38 Old Apr 6th, 2010, 8:00 am Thread Starter
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Re: JD's bearing pics

It is pretty well established that the failure of the crownwheel bearing (most common failure mode on these final drives) is not a lubrication issue.
All indications are damage to the bearing caused by stresses placed on the bearing during installation or by improper preload.

Quote:
Originally Posted by casualemt
Charley, I have wondered about the small area that is open inside the final drive, and the very small amount of lubricant that is used. thinking about the drive gearing and the bearing spinning around inside, and given that the drive has air inside it from the fill hole up, is it a possibility that by riding for an extended amount of time, the oil may heat up, and churning air into the mix may starve the bearing for lubricant? I am sure that this problem has been scrutinized from all angles, but at this point there doesn't seem to be any definitive cause..I love the video of the drive rebuild, Thanks for sharing (got cousins and sister in St. Albans and Sheldon springs)
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post #14 of 38 Old Apr 6th, 2010, 9:27 am
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Re: JD's bearing pics

So in reality the FD problem is the result of "The Good Enough" theory. That this shim is not exactly what I need, but I do not what to have to stop the line and wait for the correct size and this is very close. So this is good enough to keep working and that is what the warranty is for any way.

Or, is it more the " I'll make it fit" theory? It's a little tight, but with a little extra effort and a tap here and push there, it looks good.

????????????

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post #15 of 38 Old Apr 8th, 2010, 3:48 pm
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Re: JD's bearing pics

Quote:
Originally Posted by CharlieVT
It is pretty well established that the failure of the crownwheel bearing (most common failure mode on these final drives) is not a lubrication issue.
All indications are damage to the bearing caused by stresses placed on the bearing during installation or by improper preload.
Agreed.

Roller/ball bearings don't need much lubrication - for that matter they can have too much if they are a high speed bearing (which this is not though).

I am bothered by JZeilers note that the shaft OD of the opposing tapered roller bearing sometimes scores. That would seem like poor quality control during manufacture. Was this an isolated failure? Isn't the shaft aluminum? in which case overheating for whatever reason could have been the problem initiator.

A MN MechEngr (retired)
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post #16 of 38 Old Apr 8th, 2010, 4:56 pm
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Re: M.T.'s bearing pic

Quote:
Originally Posted by CharlieVT
I've become fairly experienced using the FD rebuild method first suggested by DMAN which uses a dial indicator to calculate preload shim thickness. I have wondered how the results of this technique would compare with the technique described in the BMW Service Manual. The BMW technique requires a special tool to stabilize the crownwheel assembly and a depth micrometer used with a machinist's block.
Results obtained using these two different methods have been very close but not exactly the same, most often within 0.05mm of eachother. The measurements between the two techniques are close enough to give me confidence in the methods.

Here are pics of the two techniques:

Comments welcome, especially from the mech. engineers and machinists in the group.
I would expect the DMAN method which measures the lash with the actual housing cover rather than the specially modified cover to be more accurate to determining the preload shim.
Have you had a chance to compare the methods on a sample of FDs and found the measurement methods to produce approximately the same difference consistently? I would expect some level variance due to manufacturing differences of the covers.

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post #17 of 38 Old Apr 8th, 2010, 5:41 pm Thread Starter
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Re: M.T.'s bearing pic

Quote:
Originally Posted by dukey33
I would expect the DMAN method which measures the lash with the actual housing cover rather than the specially modified cover to be more accurate to determining the preload shim.
Have you had a chance to compare the methods on a sample of FDs and found the measurement methods to produce approximately the same difference consistently? I would expect some level variance due to manufacturing differences of the covers.
THAT is a good question. ANS: My data is getting better as I have purchased better a better depth micrometer and have improved my technique to improve accuracy of the BMW technique. I would expect that the two techniques would provide the same result if the methods actually measure what I think they are measuring. And, YES, I have compared the techniques on a few drives and am getting pretty consistent results. Since I use different instruments (dial indicator for DMAN's method) and a depth micrometer for the BMW method there is the difference between the instruments. Even so, the results of the two methods have been giving me results very close to each other (within 0.10mm of eachother, generally less). In the case of failed drives, the difference between my measurements (which are close to each other using the two methods) and what the original shimming was, is great. I find that on failed drives the original shimming is much greater than what my measurements tell me should be in there. As testimony, I have a collection of shims that range from 0.60mm to 1.00 mm that I have replaced with shims that are often as much as 0.20mm less. Point being, the difference between the two methods is very small compared to the difference between OEM shimming of failed drives and what both methods determine as appropriate preload shimming.
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post #18 of 38 Old Apr 9th, 2010, 8:25 am Thread Starter
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Re: M.T.'s bearing pic

Quote:
Originally Posted by dukey33
I would expect the DMAN method which measures the lash with the actual housing cover rather than the specially modified cover to be more accurate to determining the preload shim.
Have you had a chance to compare the methods on a sample of FDs and found the measurement methods to produce approximately the same difference consistently? I would expect some level variance due to manufacturing differences of the covers.
Re-reading your question made me realize you may be thinking that the modified cover being used as a substitute BMW special tool is somehow involved in the measurements, which is why you point out "variance...of the covers". Yes, the parts are all a little different, but the modifed cover stabilizes the crownwheel assembly for measurement, it is not involved in the measurments themselves.

The two techniques, discounting measurement error, should provide exactly the same results. That is what I set out to try and confirm for myself, that the dial indicator method gives the same result as the BMW method. So far, the answer to that is yes, they do, within the range of some measurement error.

On variance in the parts, I have found that the shims which come in intervals of 0.10mm don't measure out exactly that. A 0.40mm shim straight from the factory might measure 0.43 or 0.44 at various point around its circumference. Also, when taking measurements for the BMW technique differences can be found at different places around the circumference of the cover. These differences are small, but exist.
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post #19 of 38 Old Apr 9th, 2010, 9:59 am
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Re: M.T.'s bearing pic

Ah, thanks for explaining that again.

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post #20 of 38 Old Apr 9th, 2010, 11:39 am
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Re: JD's bearing pics

It would be interesting to track the history of vin numbers all the way to the factory.
Does it go back to one employee,
one particular department or bench,
a certian timespan of manager or policy
shims purchased from a different supplier
or a different batch.

Do we have a Vin history of this problem?

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post #21 of 38 Old Apr 9th, 2010, 11:53 am
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Re: JD's bearing pics

Curtis,
I know you didn't want to get another FD thread started, but for what it's worth, there's been some info passed along here that's helped settle things in my mind, so thanks.

A question left for me, and likely has already been addressed, is: if one were left to find that the shimming can't be concluded to exactness, would you recommend shimming a "hair" tight, or that same "hair", loose?

Thanks again,
Frank
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post #22 of 38 Old Apr 9th, 2010, 12:10 pm
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Re: JD's bearing pics

I personally think that measuring with a dial indicator at the bearing center would be more accurate or repeatable than with a depth mike near the perimeter of a bearing. I really wish there was a way that the preload would be to a specified force, rather than a specified displacement.

Otherwise, a slightly loose bearing preload is probably better than one that is too tight.
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post #23 of 38 Old Apr 9th, 2010, 12:52 pm Thread Starter
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Re: JD's bearing pics

Quote:
Originally Posted by fpmlt
Curtis,
I know you didn't want to get another FD thread started, but for what it's worth, there's been some info passed along here that's helped settle things in my mind, so thanks.

A question left for me, and likely has already been addressed, is: if one were left to find that the shimming can't be concluded to exactness, would you recommend shimming a "hair" tight, or that same "hair", loose?

Thanks again,
Frank
Oh I don't mind yammering on about final drives, it's a hobby. But final drives threads have become as ubiquitious as oil threads and tire threads here and I figure most of the reqular readers of this board have had enough.

Some time ago a mech engineer on this site suggested that a little on the loose side is probably better than a little on the tight side as far as preload goes.

The BMW service manual specified range for preload is 0.05 to 0.10mm. So if you measure a gap from the bearing outer race to the bearing seat in the cover of 0.38mm, you would shim between 0.43mm and 0.48mm. That'd be a 0.45mm shim thickness.

In actual practice, using the two techniques I have found that the Dman dial indicator method sometimes will give me a result that is one shim thinner that the BMW Service Manual method. For example, if the dial indicator method yielded a 0.43-0.48mm range and the BMW Service Manual method yielded a 0.47- 0.52mm shim, I have used the thinner one. i.e. a 0.45mm versus a 0.50mm shim thickness.

Whether that is the best thing to do is anybodys guess.

Frankly, I suspect that 0.05mm either way probably isn't going to make a difference. Shims I have removed from drives with failed crownwheel bearings have been as much a 2.0-2.5mm thicker than what I calculated for preload for the replacement bearing; that's a lot of extra preload and a very likely cause of failure IMO. Another interest point is that I don't recall ever rebuilding a failed final drive and using more preload that what was in there. I have always used a little less or a lot less shim thickness. (There were a few drives I rebuilt before I started measuring the shim(s) that came out of the failed drives so I don't have the data on them.) I suspect that avoiding stressing the bearing by not hammering or pressing it onto the hub during installation, and getting the preload pretty close to correct will result in a drive that'll go100K miles.
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post #24 of 38 Old Apr 9th, 2010, 7:50 pm
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Re: JD's bearing pics

Quote:
Originally Posted by CharlieVT
Shims I have removed from drives with failed crownwheel bearings have been as much a 2.0-2.5mm thicker than what I calculated for preload for the replacement bearing; that's a lot of extra preload and a very likely cause of failure IMO.
Curtis

Did I read that right??
2.0-2.5 mm (0.079"-0.098") thicker than what you calculate??????? That is an incredible amount of preload!!!! There is no way the bearing would tolerate that load!!

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post #25 of 38 Old Apr 9th, 2010, 8:00 pm
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Re: JD's bearing pics

I've got about 9,000 miles on this second rebuild. So far, so good. If it goes out again, I have a FD I got off Ebay that I'll install. I won't rebuild this one again. I've found that over time my LT lost it's smoothness before the FD went out. It used to dance on the pavement like it wasn't really touching. When that goes away, that's when I start to worry. It always came back after a rebuild. I wear out a set of tires every year. I've got 67,000 on it so far. I'd like to put a LOT more on it. I'm planning another trip to northern Wisconsin in June. I'd like to make it with some confidence...............

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post #26 of 38 Old Apr 9th, 2010, 8:37 pm Thread Starter
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Re: JD's bearing pics

Quote:
Originally Posted by RealWing
Curtis

Did I read that right??
2.0-2.5 mm (0.079"-0.098") thicker than what you calculate??????? That is an incredible amount of preload!!!! There is no way the bearing would tolerate that load!!

Jim
Hi Jim,
You coming to CCR Vermont? We'd sure look forward to seeing you.

Yes, I have seen a difference of 0.20-0.25mm less in shim thickness according to my calculations many times . I have a collection of shims in the range from 0.70 to 1.00mm that I have removed from drives with failed crownwheel bearings and had to replace with much thinner shims. I never seem to find a need for those thick shims when rebuilding drives; I end up ordering shims in the 0.30 - 0.40mm range.

Now I can't really speak to the difference between bearings. Once the bearing has failed I of course can't measure it for preload, but in all these cases I was replacing the German FAG bearing with another one of the exact same nomenclature. (I don't believe that I have yet replaced one of the French 17 ball bearings that were in the supply system for a while). My understanding is that the bearing manufacturers keep their tolerances from one bearing to another pretty close (maybe you told me that?). The difference between bearings is the only unkown variable that isn't accounted for when I am comparing the shim of the failed bearing to that which I calculate for the new bearing. I am assuming that the difference in axial play between bearings is a factor of 10 or even 100 less than the differences I am seeing in calculated shim thickness. Is that a fair assumption for me to make? If it is not, then my assumption that excess preload is responsible for many bearing failures in incorrect.

Thanks.
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post #27 of 38 Old Apr 9th, 2010, 8:54 pm
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Re: JD's bearing pics

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Originally Posted by CharlieVT
Hi Jim,

Yes, I have seen a difference of 0.20-0.25mm less in shim thickness according to my calculations many times .,
Curtis

I think you slipped a decimal point in your previous post!! Hope that is not a sign of aging!!!
0.2mm is still a lot of excessive preload.

You are correct - the bearing machining tolerances are very tight.

I have signed up for CCR this year and looking forward to seeing you again. What day are you planning on arriving?
Jim

PS I've had the bike out, but today it was snowing here!!!

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post #28 of 38 Old Apr 10th, 2010, 7:35 am Thread Starter
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Re: JD's bearing pics

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Originally Posted by RealWing
........I think you slipped a decimal point in your previous post!! Hope that is not a sign of aging!!!......
Unnhhhhh...... (chagrined), yup, I certainly did move the decimal a few posts above. In the range of 0.20-mm NOT 2.0mm.

Sign of aging?.... Hey! I resemble that remark!
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post #29 of 38 Old Apr 10th, 2010, 8:56 pm Thread Starter
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DY's final drive

Here's data on another FD:

Dman's dial indicator method: 0.41-0.46mm therefore 0.45mm shim
BMW Service Manual depth micormeter method: 0.46-0.51mm therefore 0.50mm shim
The original shim in the drive was 0.80mm.
In this case I will use 0.45mm shimming which falls within the range determined by the dial indicator but is only 0.01mm below the bottom of the range determined by the depth micormeter technique.

(I've been getting consistent results with these two methods, I suspect the difference in results are either slight differences between the measuring tools used for the different techniques, althought the difference may be due to limitation of movement of the bearing in its seat in the dial micrometer method). In any case, I am finding very consistent results, point being that the method originally described by Dman does very closely produce the same results as the BMW Service Manual technique; since BMW supplies shims in intervals of 0.05mm the dial indicator method often results in a shim one increment thinner than the depth micrometer method.

Here again with this failed crownwheel bearing I find the the original shim preload was in excess of that determined by two different methods. Assuming that the replacement bearing had the same specifications as the failed bearing it would mean that the original had excess preload in the range of 0.30-0.35mm
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post #30 of 38 Old Apr 10th, 2010, 9:03 pm
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Re: DY's final drive

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Originally Posted by CharlieVT
Here again with this failed crownwheel bearing I find the the original shim preload was in excess of that determined by two different methods. Assuming that the replacement bearing had the same specifications as the failed bearing it would mean that the original had excess preload in the range of 0.30-0.35mm
Looks like more evidence that the original cause was bad pre-load at assembly. Glad you have been doing this Curtis. Guess we need to get a low mileage early rear drive that has not failed yet and check it as well. Then do a proper shim, if indicated, and see how long that one lasts.

Keep up the good work and see you up at Killington later this month.

John
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post #31 of 38 Old Apr 11th, 2010, 8:40 am
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Re: DY's final drive

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Originally Posted by jzeiler
Looks like more evidence that the original cause was bad pre-load at assembly. Glad you have been doing this Curtis. Guess we need to get a low mileage early rear drive that has not failed yet and check it as well. Then do a proper shim, if indicated, and see how long that one lasts.

Keep up the good work and see you up at Killington later this month.
I agree on a new drive and checking it. I just happen to have one and was too lazy to do it last year when I got to meet Curtis and his wife.

If his life ever allows a slot in Curtis,s life and he will have me, I would make the ride up and hang out in the area a few days to check it with him. Problem is there is SO much riding to be done up there hard to concentrate in a shop

I am just dying to see what a brand new factory drive is set up like. As I said a year ago I trust Curtis and his methodology more then I do a guy on the assembly line. I even wonder if they even try to get it right?

I really hope they are reading this, meaning BMW, as with a new LT looming if they don't get the FD right they will never be taken seriously again in the Luxury Touring World.

It is why I gather parts for my old 07, they have not listened in the 10 year run of the current LT.

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post #32 of 38 Old Apr 11th, 2010, 10:44 am Thread Starter
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Re: DY's final drive

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I agree on a new drive and checking it. I just happen to have one and was too lazy to do it last year when I got to meet Curtis and his wife.

If his life ever allows a slot in Curtis,s life and he will have me, I would make the ride up and hang out in the area a few days to check it with him. Problem is there is SO much riding to be done up there hard to concentrate in a shop

I am just dying to see what a brand new factory drive is set up like. As I said a year ago I trust Curtis and his methodology more then I do a guy on the assembly line. I even wonder if they even try to get it right?

I really hope they are reading this, meaning BMW, as with a new LT looming if they don't get the FD right they will never be taken seriously again in the Luxury Touring World.

It is why I gather parts for my old 07, they have not listened in the 10 year run of the current LT.
Sure Lee,

come on up. Once the drive is off the bike it takes me less than an hour to open and check the drive. The time consuming events are getting the drive off and back on the bike.

I'll bet BMW knows exactly what is going on at this point. The just aren't going to address the problems in a public forum. They have had a problem in the final drive manufacture/assembly department, witness more than one mode of failure of the drives of our KLTs, and FD failures of other models with similiar FDs, and failures of the Evo drives as well. Big QA issues in that dept. They just aren't going to talk about that openly.
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post #33 of 38 Old Apr 11th, 2010, 6:59 pm
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Re: DY's final drive

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Sure Lee,

come on up. Once the drive is off the bike it takes me less than an hour to open and check the drive. The time consuming events are getting the drive off and back on the bike.

I'll bet BMW knows exactly what is going on at this point. The just aren't going to address the problems in a public forum. They have had a problem in the final drive manufacture/assembly department, witness more than one mode of failure of the drives of our KLTs, and FD failures of other models with similiar FDs, and failures of the Evo drives as well. Big QA issues in that dept. They just aren't going to talk about that openly.
Thank you Curtis. Might just be a fall ride but I will work that out with you. I would rather run the gas and haul it up to you on the rear seat of the bike then pay the shipping

Yes I know they would never open up in public on the issues. But even 5 years into the LT run they did nothing, and allowed it to expire as a model without resolution. As usual it takes a guy with a "hobby" who happens to be an enthusiast to diagnose and resolve a problem.

It is why I will keep my old girl till I am gone. I gather parts, read everything I can from this forum and I am not really afraid of anything up to and including the clutch.

But the FD scared the hell out of me, still does as I am not sure I could get it right. But your work on it makes it way less of the boogie man it once was.

Actually not a thread jack but it is why I started to use a strait Moly additive. Your examinations leads you to believe that the balls in the race become rough, stop spinning in their chase, and then destroy the race cage, and it gets way ugly from there. I think that is correct, right?

Moly actually "heals" rough microscopic irregularity's in gears and I would hope ball bearings and the chase they ride in.

I realize nothing will keep an improperly set FD from destruction over time, but I keep hopeful that Hans was in a great mood doing mine, got laid the night before, and was into his work on that day. Hopefully the Moly keeps it humming along.

Lee
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Re: JD's bearing pics

I would not worry too much Lee as it appears they got the pre-load right after the 2002 model year. There just have not been that many late model drives that have failed and the 05 and up that have were the aluminum end of the crown wheel and it's small tapered bearing. The EVO drives are a different story as those are sealed bearings and the oil is just for the gears.


Drive with impunity I say!!!

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post #35 of 38 Old Apr 11th, 2010, 9:55 pm
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Re: DY's final drive

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Originally Posted by CharlieVT
Sure Lee,

come on up. Once the drive is off the bike it takes me less than an hour to open and check the drive. The time consuming events are getting the drive off and back on the bike.

I'll bet BMW knows exactly what is going on at this point. The just aren't going to address the problems in a public forum. They have had a problem in the final drive manufacture/assembly department, witness more than one mode of failure of the drives of our KLTs, and FD failures of other models with similiar FDs, and failures of the Evo drives as well. Big QA issues in that dept. They just aren't going to talk about that openly.
Charlie, you are more optimistic than me! I will believe they understand the problem when I see them correct it on a future design.
:-)

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post #36 of 38 Old Apr 12th, 2010, 6:41 am Thread Starter
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Re: DY's final drive

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Charlie, you are more optimistic than me! I will believe they understand the problem when I see them correct it on a future design.
:-)
If they conclude, as I have, that the problem isn't with the design but rather a QA manufacturing/assembly issue then they don't really need to redesign it. They just need to build 'em better. And witness: the Evo drive was a new design and those had a failure rate too. It isn't the design. Don't call me a BMW apologist, but I think the BMW engineers knew what they were doing. The machinists and assembly guys were making mistakes for whatever reason, maybe they were hungover, were commiting sabotoge, or, my favorite theory: former Soviet block East German workers with bad work ethic (that's a good theory if you go back and read some management articles about problems with the work ethic in the labor force following reunification in Germany).
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post #37 of 38 Old Apr 14th, 2010, 8:52 pm
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Re: DY's final drive

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If they conclude, as I have, that the problem isn't with the design but rather a QA manufacturing/assembly issue then they don't really need to redesign it. They just need to build 'em better. And witness: the Evo drive was a new design and those had a failure rate too. It isn't the design. Don't call me a BMW apologist, but I think the BMW engineers knew what they were doing. The machinists and assembly guys were making mistakes for whatever reason, maybe they were hungover, were commiting sabotoge, or, my favorite theory: former Soviet block East German workers with bad work ethic (that's a good theory if you go back and read some management articles about problems with the work ethic in the labor force following reunification in Germany).
Well, having been an engineer for the past 27 years, I have a passing acquaintance with design concepts and principles. Design is a many faceted exercise and designing a component or system that works well if perfectly assembled is relatively easy. The difference between a bad design, a good design and an excellent design is as follows:

bad design - doesn't meet the requirements no matter how well it is made.

good design - meets the requirements if properly assembled.

excellent design - meets the requirements and virtually can't be assembled incorrectly.

The BMW deisgn may be a good design, but it certainly isn't an excellent design. The issues may well be assembly related and the root cause of the assembly errors may well be as you hypothesize. However, if BMW had used appropriate DFA/DFM, then the variation in assembly outcomes would not be nearly so great.

This reminds me somewhat of the Hyatt Regency walkway collapse in Kansas City a number of years ago as chronicled in the book "To Engineer is Human." As an aside, this is a great book and you don't have to be an engineer to read and appreciate it. The walkway as originally designed wasn't compliant with the prevailing structural code, but very likely would have never failed due to the margin of safety in such codes. However, the problem was that the original design was essentially impossible to build. This resulted in a field change to the design which inadvertantly changed the load path such that one part of the structure now carried twice the load it would have carried in the original design. This was the primary cause of the structural failure, with the inadequate capacity of the original design being a secondary factor. The engineer who made the field change screwed up by not properly analyzing the new load path, but in my opinion the original engineer is the one to blame. Making a design that can't reasonably be built is simply not acceptable design practice.

It may well be that the design is adequate if perfectly assembled, but the assembly process is sufficiently complex and with enough "degrees of freedom" in assembly that it simply can't be reliably assembled correctly in a typical production environment with typical factory labor. And the tolerance for improper assembly (preload, etc.) isn't very good.
To me, this is as much of a design error as is a design that is inadequate even if perfectly assembled. They are design errors of a different type, but design errors nontheless.

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post #38 of 38 Old Apr 15th, 2010, 9:03 am Thread Starter
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Re: DY's final drive

[QUOTE=Voyager].......
The BMW design may be a good design, but it certainly isn't an excellent design. The issues may well be assembly related and the root cause of the assembly errors may well be as you hypothesize. However, if BMW had used appropriate DFA/DFM, then the variation in assembly outcomes would not be nearly so great......
QUOTE]

Your comments mirror those made by me some time ago in prior posts. Making things "sailor proof" was a term we used in the Navy to describe making things simple enough that the average Blue Jacket couldn't screw it up; analogous to your "engineering excellence" where the design makes the unit tolerant of assembly errors. However, I don't see that the assembly procedures for these final drives that are failing as being anymore complicated that the crankcase or tranny of so many BMW machines. The techniques needed to calculate the end play shims of crankshafts, countershafts in the engine, and transmission shafts are very similar. I have rebuilt transmissions of 1970s BMW Airheads, and there are similar assembly procedures. Most of those transmissions have stood the test of time pretty well, as have the majority of the final drives on KLTs. So, yes, maybe BMW engineers could have build the final drive in such a way as to be more tolerant of assembly "screwups", but I don't see the final drive as anymore susceptible of assembly errors than so many other components. I really conclude that there were real QA problems (for whatever reason) in the final drive assembly section. Who knows, there may have been one bad actor with a drinking problem, an ax to grind, or a passive-aggressive personality disorder.
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