What are the suspected reasons for final drive failures - BMW Luxury Touring Community
 
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post #1 of 50 Old Jan 24th, 2011, 8:48 pm Thread Starter
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What are the suspected reasons for final drive failures

I tried using the search engine on this site to find the stats on LT bikes that have had a final drive failure. No luck. Is it certain years, mileage, frequency of changing the oil, type of oil, loads carried or any of these. I've heard there was a correlation with the final drive bearing having either 17 or 19 balls in the race, with the 19 ball bearings being more prone to failure due to the smaller size of the balls.

I suspect this is an old subject. If this has been discussed in detail before please direct me to the thread.

My thinking is check the play, drop the oil, check the plug, fill it and go ride. Call Ryder as necessary.

Thanks
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post #2 of 50 Old Jan 24th, 2011, 8:58 pm
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Re: What are the suspected reasons for final drive failures

This subject is an on going hot topic. Luckily we have our final drive guru, CharleyVT. check out his posts, he has really done some indepth studies of failed final drives. Most popular opinion on failure is improper preload shimming by the factory. This is why some LT's go forever without failure and others do not. Bad factory setup.

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post #3 of 50 Old Jan 24th, 2011, 11:23 pm
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Re: What are the suspected reasons for final drive failures

While some of us have had the oil wet rear wheel and sinking feeling of a bearing failure only to find bearing was just fine having instead just a seal failure ... go figure

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post #4 of 50 Old Jan 25th, 2011, 7:35 am
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Re: What are the suspected reasons for final drive failures

I will decline the appellation of "guru", but I have been following reports of final drive failures for years now and have rebuilt about 30 of them. There are others who understand these things much better than I do, but are unwilling to share their knowledge or waste their time (bmw folks themselves, professional mechanics or engineers.)

Failure modes: The most common catastrophic failure is of the crown wheel bearing (this is the bearing that is commonly a 19 ball German bearing, but for a period on time BMW supplied a 17 ball French made bearing). I'll discuss my theories as to why these bearings have failed further below in this post.

There are two other less common causes of catastrophic failure that I am aware of: these involve the tapered roller bearing located at the opposite end of the crown gear assembly from the crown wheel bearing. In the case of primarily 2005 models, there is a lack of an interference fit of the tapered roller bearing on its shaft on the crown gear assembly. This has resulted in the tapered roller bearing spinning on its shaft leading to eventual failure.

Another mode of failure I have seen a couple of times is more unusual: in these cases the inner race of the input pinion shaft needle roller bearing slips down its seat on the pinion shaft and wears through the bottom of its recess in the final drive housing to the point where it can damage the tapered roller bearing. In the case of one final drive shipped to me, the inner race of the pinion shaft needle bearing had slipped of its seat and worn through the housing far enough to dislodge the speedometer sensor sending ring. The only symptom at that point was that the speedometer wasn't working; if this were to happen on a later year bike without the speedometer sending ring, the first symptom probably would have been catastrophic failure of the tapered roller bearing because that would have been the next thing damaged by the dislodged needle bearing race. This type of unusual failure has been photographed and reported on this board.

Addendum added by edit: Another mode of failure that I have seen first hand, and have read additional reports of is a failure of the press fit between the carbon steel and aluminum components of the crown gear assembly. This part is factory assembled and only available as part of a crown gear/pinion shaft set. In this failure, the interference fit between the carbon steel crown gear and the aluminum component is inadequate and slippage occurs between these two components. This failure was written up in a past issue of BMWON and was also seen by a member of this board who had FD lube come out the rear wheel bolt holes during a tire change. (another example of machining errors resulting in improper fitment between components).

Other final drive "failures" include leaking seals at both the rear wheel hub and the input pinion shaft. Any seal can leak without associated failure of mechanical parts and there have undoubtedly been a few of these.

I believe there have been reports of failure of the input pinion shaft assembly but these are very rare compared to the "classic" crown wheel bearing failure.

The "classic" crown wheel bearing failure:

Two oft repeated questions relating to the most common failure, that of the crown wheel bearing, are: 1) What is/are the cause(s), (the implication being is there something that can be done to prevent it?), and 2) Are there any signs of impending failure that would provide early warning that might help avoid a breakdown on the road?

1) Causes: Having rebuilt a number of drives with failed crown wheel bearings and having used two separate methods to measure for bearing preload as specified in the BMW service manual, I have consistently found that drives were delivered with excess preload. Consequently, I suspect that excess axial forces on the crown bearing result in eventual damage to the balls and races leading to bearing failure. Another possible cause might be that improper forces were used during bearing installation damaging the bearing. I do not believe that there is any evidence of superiority of the 19 ball bearing over the 17 ball bearing or vice versa.

IMO the root causes of all these failures is a lack of quality assurance in either the machining of FD components or in the assembly procedures.

2) Predicting failure: The evidence is pretty good that early warning signs are hard to come by. The reports of failure seem to suggest that the amount of time or number of miles between finding significant metal in the FD lube, or first feeling roughness in rotation of the rear wheel and ultimate seal failure and oil loss is small.

Some folks have proposed chip detectors as found on some aircraft but I haven't heard on anyone actually fabricating one (and I doubt it would provide much benefit); others have speculated that monitoring FD temperature might provide early warning, and someone on this board posted about actually fabricating one. I haven't read any posts about that effort, but I doubt monitoring temp would do much to predict a failure.

Two indicators that the FD crown wheel bearing is going bad are shiney metal flakes in the oil and roughness felt during wheel rotation. The “shake the wheel test” is often suggested as a test of final drive problems but I don’t believe it has any value in assessing the final drive; it will reveal loose pivot bearings or other swing arm problems. By the time looseness is felt at the rear wheel secondary to crown wheel bearing failure, there is probably already seal failure and loss of lube. One test I do put some stock in is feeling for roughness during wheel rotation; to do this I suggest pushing the brake pads back so they are not touching the rotor, or simply removing them, and then slowly rotating the rear wheel while feeling for roughness. Someone also suggested listening to the FD with a mechanic’s stethoscope while rotating the rear wheel, but I suspect feeling for roughness would be a better indicator. But again, by the time you can feel roughness during wheel rotation, by all accounts there are few few miles left before catastrophic bearing failure.

While really meaningful statistics are lacking, it seems that the earlier models 99-03 may have had the higher failure rates, but there have been reports of FD failure as late as the 2009 model.

Unfortunately, I have concluded that the only preventive measure beyond following the manufacturer's recommended lubrication intervals is preemptive rebuild of the final drive. Preemptive rebuild should include careful measurement of preload rather the just swapping out the bearing. The evidence is pretty good that rebuilding a failed drive by just replacing the bearing sets the stage for a repeat failure. More than one rider has reported multiple FD failures following BMW service department repair; I have to wonder how those rebuilds were done.

Summary conclusions: There are no “early” indications of crown wheel bearing failure. Roughness felt during wheel rotation or shiny metal flakes in the lube indicate that bearing failure has started, and few miles are left before the bearing retainer breaks and seal integrity is lost.

Last edited by CharlieVT; Jan 25th, 2011 at 9:40 am.
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post #5 of 50 Old Jan 25th, 2011, 9:19 am
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Re: What are the suspected reasons for final drive failures

CharlieVT,

Very informative! Thanks for a great writeup.
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post #6 of 50 Old Jan 25th, 2011, 3:34 pm
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Re: What are the suspected reasons for final drive failures

I should have given credit in my post above to those gentlemen who have contributed to what I think we understand about the K1200LT final drives and how they fail. The original post by Dman who gave us the dial indicator method off measuring for preload, and the many posts by several mechanical engineers on this site who have offered observations, experiences, and insight relating to how the final drive is constructed and factors that might be contributing to failure.
All I think I know is based on my observations and their knowledgeable input. This has been a team effort and credit goes to all who have contributed.
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post #7 of 50 Old Jan 25th, 2011, 4:32 pm
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Re: What are the suspected reasons for final drive failures

Quote:
Originally Posted by CharlieVT
I will decline the appellation of "guru", but I have been following reports of final drive failures for years now and have rebuilt about 30 of them. There are others who understand these things much better than I do, but are unwilling to share their knowledge or waste their time (bmw folks themselves, professional mechanics or engineers.)
Charlie does an in-depth explanation, succinct and to the point and he declines the "GURU" label??? There are those that walk the walk and there are those that talk the talk... Charlie does them both... and rather eloquently if I do say so myself...

Nicely done sir! And a huge THANK-YOU to all those who helped contribute... and continue to provide valuable info...

I am but a minion...


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post #8 of 50 Old Jan 25th, 2011, 6:21 pm
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Re: What are the suspected reasons for final drive failures

Quote:
Originally Posted by UncleMark
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post #9 of 50 Old Jan 25th, 2011, 8:41 pm
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Talking Re: What are the suspected reasons for final drive failures

Final drives never fail! That is a myth started by jealous Wing riders!
Just ask BMW and they will tell you the same thing...!

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post #10 of 50 Old May 28th, 2012, 8:28 am
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Re: What are the suspected reasons for final drive failures

Quote:
Originally Posted by CharlieVT

Some folks have proposed chip detectors as found on some aircraft but I haven't heard on anyone actually fabricating one (and I doubt it would provide much benefit); others have speculated that monitoring FD temperature might provide early warning, and someone on this board posted about actually fabricating one. I haven't read any posts about that effort, but I doubt monitoring temp would do much to predict a failure.
Any news on either of these systems being designed/made by now?
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post #11 of 50 Old May 28th, 2012, 9:20 am
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Re: What are the suspected reasons for final drive failures

Quote:
Originally Posted by earthman
Any news on either of these systems being designed/made by now?
I haven't heard of any, probably with good reason. Even if such proposed detection devices were to work, the amout of advance notice is very limited.
Read past posts regarding that document the rapidity of bearing degradation.
For the trouble and expense of installing an "early detection device" you can do a preemptive rebuild on your FD.
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post #12 of 50 Old May 28th, 2012, 10:15 am
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Re: What are the suspected reasons for final drive failures

There is a device. I know nothing about it and did not pay attention to it.
dc
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post #13 of 50 Old May 28th, 2012, 10:56 am
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Re: What are the suspected reasons for final drive failures

While I am NOT here to debate Charlie's "GURU" status ... because he certainly is worthy of the title ... I would like to throw in my two cents.

My '06 GT's drive failed in Nevada. The cause was very clear to me, and I have yet to read this mentioned in this thread.

My final drive failed due to my incessant need to ride my bike. Had I just left her parked, it would have never failed.

Hope this helps. You've been warned.

- Joe
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post #14 of 50 Old May 28th, 2012, 3:26 pm
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Re: What are the suspected reasons for final drive failures

Great to read an "old timer" and contributor to this site "Messenger13"!

""For the trouble and expense of installing an "early detection device" you can do a preemptive rebuild on your FD."" CharlieVT.

I think there are others who have FD warning devices but mine may be the only one that uses the existing FD sump and a "chip detector". In tests it "warns" (speaker) and has a "red" warning light. It digitally resets and rearms it self and can be tested via a button push even when underway. It is a true Final Drive Warning System. I posted it on here some years ago and it has been working on my 99 K12LT ever since.

It is true what has been said about the short time that it takes for the crown bearing to begin to disintegrate. Subjective operator induced radial/axial wheel shake (bike on center stand) or FD fluid changes are hard pressed to detect incipient failure. But, early detection is important. It can save your FD from trashing itself where a simple crown bearing renew with proper axial "preload" can then be done.

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post #15 of 50 Old May 28th, 2012, 5:22 pm
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Re: What are the suspected reasons for final drive failures

Well summarised (again) Curtis, great job. As I have suggested recently, and as you also state, what we have with the crown wheel ball bearing problem is known in industry as "short lead time to failure" and typically the only way to manage this type of issue on machines is by on-line vibration monitoring whereby known levels are set at alarm and shutdown points in order to prevent catastrophic failures.
In our case though, I still intend to connect our vibration analyser to the FD and try to get some meaningful data, but as with all VA exercises we need historical data for comparison, and ideally we also need to see a vibration spectrum from a FD unit with a known "over-preloaded" bearing. My '05 has 27,000 Km's and no fuzz on the mag plug (yet), but like you, I feel this really doesn't tell me much as I may not yet be into the beginning of the pF curve (failure potential), and if/when I do get to that point no-one really knows how short the lead time to failure is. So to shorten this already long story, I guess my 12,000-odd kilometre trip across the continent and return in September may add something more to my story, we'll see.

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post #16 of 50 Old May 28th, 2012, 7:07 pm
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Re: What are the suspected reasons for final drive failures

Hi Dennis,

Thanks for you post. I always enjoy reading your input.

So you are going to ride 12,000 kilometers across the continent? You going to be running some kind of VA during the ride?

Have a great trip.

For those who are experimenting with early detection with chip or heat sensors, I offer every encouragement. Nothing wrong with seeking earliest possible indication of a bearing failure. It is just that based on all I think I know of how these FD fail, if someone is on a long distance trip, a chip detector isn't going to make much difference. It might give you some extra miles of warning before the ride starts to feel rough but how many miles is unknown. That's why I say to those who are looking for "road insurance" a chip detector is going to be of limited benefit. I maintain that the best FD road insurance is a rebuild of the drive with replacement of the crownwheel bearing with proper setup, inspection of the tapered roller bearing and the input pinion needle bearing race. I think it makes sense to do that before investing in a chip detector. (I hesitate to repeat this because it will be construed as a solicitation by me to rebuild drives, which simply isn't the case.)




Quote:
Originally Posted by K100Dennis
Well summarised (again) Curtis, great job. As I have suggested recently, and as you also state, what we have with the crown wheel ball bearing problem is known in industry as "short lead time to failure" and typically the only way to manage this type of issue on machines is by on-line vibration monitoring whereby known levels are set at alarm and shutdown points in order to prevent catastrophic failures.
In our case though, I still intend to connect our vibration analyser to the FD and try to get some meaningful data, but as with all VA exercises we need historical data for comparison, and ideally we also need to see a vibration spectrum from a FD unit with a known "over-preloaded" bearing. My '05 has 27,000 Km's and no fuzz on the mag plug (yet), but like you, I feel this really doesn't tell me much as I may not yet be into the beginning of the pF curve (failure potential), and if/when I do get to that point no-one really knows how short the lead time to failure is. So to shorten this already long story, I guess my 12,000-odd kilometre trip across the continent and return in September may add something more to my story, we'll see.
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post #17 of 50 Old May 28th, 2012, 8:38 pm
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Re: What are the suspected reasons for final drive failures

No Curtis, not during the trip, not possible with the gear we use. I'm going to try to get some meaningful data off the drive with it running at a constant speed. I think it will be possible, but I'll need to set the rear wheel on some rollers to simultate load in the correct orientation (pressing down on the wheel rather than suspending the wheel on the centre stand, though we may also do that as well, just to see what differences are seen, if any).
As for the trip, and risk associated with FD failure - the bike will be loaded to the full 600 Kg gross limit, and we'll be doing around 700 to 800 Km's dailly for the trip across the Nullarbor to Western Australia and same on return, the rest of the time will be tourist type mileage etc. Away in total for 4 weeks. If I have a problem it'll be the roadside assist number from the cell phone, then borrow my brother-in-law's R1200GS I guess, but I'm not counting on that as an issue. Ride it and enjoy I say. I reckon my '05 is a 96%er.

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post #18 of 50 Old May 28th, 2012, 11:01 pm
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Re: What are the suspected reasons for final drive failures

Do the newer units, for the RT, such as since 08 or so still use the preload? I had been led to believe that the preload was no longer done on the newest final drives.
Am I wrong?
dc
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post #19 of 50 Old May 28th, 2012, 11:17 pm
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Re: What are the suspected reasons for final drive failures

My opinion - Most of the heat generated in a FD is due to the oil being churned by the gearset. Very little will be from bearing load, and even less will be from a failed bearing. The nature of the metal on the magnet is the best first indication.
MN MechEngr
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post #20 of 50 Old May 29th, 2012, 5:34 am
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Re: What are the suspected reasons for final drive failures

Quote:
Originally Posted by David13
Do the newer units, for the RT, such as since 08 or so still use the preload? I had been led to believe that the preload was no longer done on the newest final drives.
Am I wrong?
dc
You're correct, they use a needle bearing where they used to use a tapered bearing..
The main bearing is shimmed to set the backlash, no preload.
This style from 05 on the RT, IIRC, which has also been known to fail. This bearing is not lubed by the FD oil, sealed bearing. Can't use the over shim reasoning on this one. The P/N has changed for the replacement bearing.
Seems more to do with their design of a single sided FD then shimming but enough about FD's

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post #21 of 50 Old May 29th, 2012, 5:48 am
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Re: What are the suspected reasons for final drive failures

Quote:
Originally Posted by David13
Do the newer units, for the RT, such as since 08 or so still use the preload? I had been led to believe that the preload was no longer done on the newest final drives.
Am I wrong?
dc
You are correct. I've made a hobby of the K1200LT Final Drive which has a design common to earlier RTs and GSs (and probably other models as well). This FD has a tapered roller bearing at one end of the crown gear assembly which requires a preload.

The Evo Final Drive (listed as a "right angle gear box" on BMW parts fische; the one with the hole in it.) does not have a tapered roller bearing. Rather, it has a needle bearing located similiarly to where the tapered roller bearing is in earlier FDs. The Evo FD has "adjusting washers" and "spacer rings" for setting up the tolerances but it doesn't have a "preload" since it doesn't have a tapered roller bearing.

Here's a very nice site which pictures and describes the two types of FDs. Mostly about the earlier, K1200LT type FD, but scroll down to read a paragraph about the Evo drive.
I've heard of problems with the Evo drives, but I've never worked on one, and am unfamiliar with the problems. What I have written about on this site regarding FDs is not applicable to the Evo FD.
BTW: the following link is to an article by Anton Largiader who has a BMW shop in Charlottesville, VA, Virginia Motorrad. I don't know him personally, but I have repeatedly suggested that anyone looking to have a FD rebuilt, Anton's shop would undoubtedly be a good choice.
Here's his explaination of the final drives:

http://www.bmwra.org/otl/finaldrive/

Last edited by CharlieVT; May 29th, 2012 at 5:59 am.
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post #22 of 50 Old May 29th, 2012, 6:15 am
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Re: What are the suspected reasons for final drive failures

Quote:
Originally Posted by New2rt
You're correct, they use a needle bearing where they used to use a tapered bearing..
The main bearing is shimmed to set the backlash, no preload.
This style from 05 on the RT, IIRC, which has also been known to fail. This bearing is not lubed by the FD oil, sealed bearing. Can't use the over shim reasoning on this one. The P/N has changed for the replacement bearing.
Seems more to do with their design of a single sided FD then [sic] shimming but enough about FD's
I can't speak to the design of the Evo drive, but after years of reading the thoughts of mechanical engineers on the design of the K1200LT final drive, and having analyzed the various failures of these drives, I'm pretty well convinced that the problems stem from manufacturing (machining) of FD components and assembly procedures.

If it were a design issue we wouldn't be seeing FDs go 200,000+ miles without problems, and we would be hearing of many more failures than we are.
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post #23 of 50 Old May 29th, 2012, 6:35 am
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Re: What are the suspected reasons for final drive failures

Quote:
Originally Posted by CharlieVT
I can't speak to the design of the Evo drive, but after years of reading the thoughts of mechanical engineers on the design of the K1200LT final drive, and having analyzed the various failures of these drives, I'm pretty well convinced that the problems stem from manufacturing (machining) of FD components and assembly procedures.

If it were a design issue we wouldn't be seeing FDs go 200,000+ miles without problems, and we would be hearing of many more failures than we are.

I'm referring to the RT drive, no preload so you can't blame over shimming.
Design is a broad brush stoke to include the bearing, oil capacity, life time fluid, etc.
Some make it past 200k is not an answer to a failure and doesn't reason it away.

On the LT drive failures I would index the outer race position before cutting open to look for a common wear area if there is one (top outer, bottom inner).

BMW has many issues with their drives from simple leaks to major failures to include drive shafts coming apart at speed.

I don't have a dog in this fight, was just trying to answer david13s question.

I spelled then incorrectly?

Last edited by New2rt; May 29th, 2012 at 6:48 am.
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post #24 of 50 Old May 29th, 2012, 8:44 am
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Re: What are the suspected reasons for final drive failures

Quote:
Originally Posted by New2rt
I'm referring to the RT drive, no preload so you can't blame over shimming.
Design is a broad brush stoke to include the bearing, oil capacity, life time fluid, etc.
Some make it past 200k is not an answer to a failure and doesn't reason it away.

On the LT drive failures I would index the outer race position before cutting open to look for a common wear area if there is one (top outer, bottom inner).

BMW has many issues with their drives from simple leaks to major failures to include drive shafts coming apart at speed.

I don't have a dog in this fight, was just trying to answer david13s question.

I spelled then incorrectly?
Hiya Howard,
Thanks for posting to clarify.
Yeah, I don't really know about the Evo FD problems, could be design, parts quality, assembly, all of the above.... someone probably knows, but I sure don't.
My hobby has been to understand the K1200LT FD and it's associated problems, no doubt to the point of tedium for some readers on this board. Much of what I state is repetition of what I have posted before, however, many folks are coming to the K1200LT as newbees, and asking the same old questions.
I have no dog to fight either, but rather just trying to share what I think I know and clarify things so that folks reading about their KLT final drive here get to share in the knowledge that has been accumulated not only by me, but by the group on this site over the years. Many knowledgeable mechanical engineeers, professional mechanics, and others have contributed. I just try to distill all the info.

Sorry for pinging on you for grammer, just trying to show my efforts to be precise to the point of being obnoxious; I've posted more than my share of typo's, grammatical errors, and out right blunders.

See if I got this right, "then" vs "than": http://www.wikihow.com/Use-Than-and-Then

In Friendship,
Curtis

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post #25 of 50 Old May 29th, 2012, 9:15 am
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Re: What are the suspected reasons for final drive failures

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Originally Posted by messenger13_ver2
While I am NOT here to debate Charlie's "GURU" status ... because he certainly is worthy of the title ... I would like to throw in my two cents.

My '06 GT's drive failed in Nevada. The cause was very clear to me, and I have yet to read this mentioned in this thread.

My final drive failed due to my incessant need to ride my bike. Had I just left her parked, it would have never failed.

Hope this helps. You've been warned.
How many miles had the bike done then?
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post #26 of 50 Old May 29th, 2012, 9:16 am
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Re: What are the suspected reasons for final drive failures

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Originally Posted by CharlieVT
I can't speak to the design of the Evo drive, but after years of reading the thoughts of mechanical engineers on the design of the K1200LT final drive, and having analyzed the various failures of these drives, I'm pretty well convinced that the problems stem from manufacturing (machining) of FD components and assembly procedures.

If it were a design issue we wouldn't be seeing FDs go 200,000+ miles without problems, and we would be hearing of many more failures than we are.
You are right on, Curtis! As you know, I have been following this topic for several years now, and based on everything that I have read, both here and in other forums, and my own analysis, I am convinced that these problems are very much "manufacturing" quality issues.

FYI, I am very sure that the axial preload that is applied by the shims are designed to make that preload be at the maximum level of the design tolerance for the deep-groove ball bearing of the crown gear bearing. Why? The largest axial load on the assembly comes from the thrust of the worm gear onto the crown gear (refer to the excellent write up that we all had looked at a few years back, and you had refereed to earlier - http://www.bmwra.org/otl/finaldrive/). This thrust is in the opposite direction to the preload applied by the shims, and therefore has to be cancelled out before any axial load is passed onto the bearing itself.

So, if the proper axial preload is at the maximum of the design limit for the bearing, then over-shimming will push the axial preload pass that maximum, ergo bearing failures!

The FD for the R bikes changed with the beginning of R1200. The design relies on the ball bearing to take up the axial loading. These deep groove ball bearings are designed to be able to handle up to about 50% of the radial load, axially. Note that the thrust of the worm gear onto the crown gear is offset from the center line of the crown gear, which means that the force has a twisting "moment" on the ball bearing. In your LT FD, the taper ball bearing takes care of that, while for the EVO FD, the needle roller bearing on the axle assembly takes care of that load.

Pad. Gajajiva
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post #27 of 50 Old May 29th, 2012, 9:36 am
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Re: What are the suspected reasons for final drive failures

Thank you
I'm familiar with Anton, and I've seen your videos before as well.
I suppose if I review it all enough, I will learn and be able to understand the issues. And then remember.
I do like your analysis that it's not design.
And I think the reasoning is good on that.
Some people emphasize the single side arm idea. But every front wheel drive car is a type of single side arm, or supported only from one side, with no major issues.
So if it's done right, it can be done.
dc
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post #28 of 50 Old May 29th, 2012, 12:17 pm
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Re: What are the suspected reasons for final drive failures

Quote:
Originally Posted by PadG
....based on everything that I have read, both here and in other forums, and my own analysis, I am convinced that these problems are very much "manufacturing" quality issues.

FYI, I am very sure that the axial preload that is applied by the shims are designed to make that preload be at the maximum level of the design tolerance for the deep-groove ball bearing of the crown gear bearing. Why? The largest axial load on the assembly comes from the thrust of the worm gear onto the crown gear (refer to the excellent write up that we all had looked at a few years back, and you had refereed to earlier - http://www.bmwra.org/otl/finaldrive/). This thrust is in the opposite direction to the preload applied by the shims, and therefore has to be cancelled out before any axial load is passed onto the bearing itself.

So, if the proper axial preload is at the maximum of the design limit for the bearing, then over-shimming will push the axial preload pass that maximum, ergo bearing failures!

The FD for the R bikes changed with the beginning of R1200. The design relies on the ball bearing to take up the axial loading. These deep groove ball bearings are designed to be able to handle up to about 50% of the radial load, axially. Note that the thrust of the worm gear onto the crown gear is offset from the center line of the crown gear, which means that the force has a twisting "moment" on the ball bearing. In your LT FD, the taper ball bearing takes care of that, while for the EVO FD, the needle roller bearing on the axle assembly takes care of that load.
Pad,
Thanks for this post. It helps to build a mental picture of the dynamics inside the FD under load.

And while I am being my boorish, picayune self, (Insenitive Moron? - old timers on this site will recall the appellation of "insenitive moron"... ), isn't it a pinion gear and not a worm gear?

Pinion gear pics:
http://www.google.com/search?q=pinion+gear+pic
Worm gear pics:
http://www.google.com/search?q=worm+gear+pic

All in fun,
best regards
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Re: What are the suspected reasons for final drive failures

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Originally Posted by PadG
You are right on, Curtis! As you know, I have been following this topic for several years now, and based on everything that I have read, both here and in other forums, and my own analysis, I am convinced that these problems are very much "manufacturing" quality issues.

FYI, I am very sure that the axial preload that is applied by the shims are designed to make that preload be at the maximum level of the design tolerance for the deep-groove ball bearing of the crown gear bearing. Why? The largest axial load on the assembly comes from the thrust of the worm gear onto the crown gear (refer to the excellent write up that we all had looked at a few years back, and you had refereed to earlier - http://www.bmwra.org/otl/finaldrive/). This thrust is in the opposite direction to the preload applied by the shims, and therefore has to be cancelled out before any axial load is passed onto the bearing itself.

So, if the proper axial preload is at the maximum of the design limit for the bearing, then over-shimming will push the axial preload pass that maximum, ergo bearing failures!

The FD for the R bikes changed with the beginning of R1200. The design relies on the ball bearing to take up the axial loading. These deep groove ball bearings are designed to be able to handle up to about 50% of the radial load, axially. Note that the thrust of the worm gear onto the crown gear is offset from the center line of the crown gear, which means that the force has a twisting "moment" on the ball bearing. In your LT FD, the taper ball bearing takes care of that, while for the EVO FD, the needle roller bearing on the axle assembly takes care of that load.
The crown gear load will increase the preload on the ball bearing not cancel it, if what you say is true it will unload the taper roller bearing, not the ball bearing. The shims are there to preload the taper bearing. The crown gear should not be loaded against the pinion, that's why there is a backlash spec.
I'll spend more time reading the article.
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post #30 of 50 Old May 29th, 2012, 12:26 pm
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Re: What are the suspected reasons for final drive failures

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Originally Posted by CharlieVT
Hiya Howard,
Thanks for posting to clarify.
Yeah, I don't really know about the Evo FD problems, could be design, parts quality, assembly, all of the above.... someone probably knows, but I sure don't.
My hobby has been to understand the K1200LT FD and it's associated problems, no doubt to the point of tedium for some readers on this board. Much of what I state is repetition of what I have posted before, however, many folks are coming to the K1200LT as newbees, and asking the same old questions.
I have no dog to fight either, but rather just trying to share what I think I know and clarify things so that folks reading about their KLT final drive here get to share in the knowledge that has been accumulated not only by me, but by the group on this site over the years. Many knowledgeable mechanical engineeers, professional mechanics, and others have contributed. I just try to distill all the info.

Sorry for pinging on you for grammer, just trying to show my efforts to be precise to the point of being obnoxious; I've posted more than my share of typo's, grammatical errors, and out right blunders.

See if I got this right, "then" vs "than": http://www.wikihow.com/Use-Than-and-Then

In Friendship,
Curtis
Huh, I thought you used than with a number such as one is less than two.
Somebody once taught me to remember it by th(an -a number) guess they were wrong.
Live and learn.
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post #31 of 50 Old May 29th, 2012, 12:28 pm
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Re: What are the suspected reasons for final drive failures

Quote:
Originally Posted by David13
Thank you
I'm familiar with Anton, and I've seen your videos before as well.
I suppose if I review it all enough, I will learn and be able to understand the issues. And then remember.
I do like your analysis that it's not design.
And I think the reasoning is good on that.
Some people emphasize the single side arm idea. But every front wheel drive car is a type of single side arm, or supported only from one side, with no major issues.
So if it's done right, it can be done.
dc
I couldn't possible tell you how many front wheel drive bearings I replaced, there has been that many.
It's far from the same thing as a single sided swing arm.
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post #32 of 50 Old May 29th, 2012, 12:38 pm
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Wink Re: What are the suspected reasons for final drive failures

Quote:
Originally Posted by CharlieVT
Pad,
Thanks for this post. It helps to build a mental picture of the dynamics inside the FD under load.

And while I am being my boorish, picayune self, (Insenitive Moron? - old timers on this site will recall the appellation of "insenitive moron"... ), isn't it a pinion gear and not a worm gear?

Pinion gear pics:
http://www.google.com/search?q=pinion+gear+pic
Worm gear pics:
http://www.google.com/search?q=worm+gear+pic

All in fun,
best regards
Ok, picky!!! You got me. It is a pinion gear. When I write something like this, my mind is deep in my thought rather than what I am writing.......at least, that's my excuse.

Pad. Gajajiva
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1960 Triumph Bonneville (T120)
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post #33 of 50 Old May 29th, 2012, 12:49 pm
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Re: What are the suspected reasons for final drive failures

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Originally Posted by New2rt
The crown gear load will increase the preload on the ball bearing not cancel it, if what you say is true it will unload the taper roller bearing, not the ball bearing. The shims are there to preload the taper bearing. The crown gear should not be loaded against the pinion, that's why there is a backlash spec.
I'll spend more time reading the article.
See the contradiction in your statement that I'd highlighted? The crown gear is not loaded against the pinion. I cannot be. A certain gap is required, and that is controlled by the relative position of the taper bearing's inner race on the aluminum half-shaft. BTW, do keep in mind that the ball bearing has a radial preload as well.

Pad. Gajajiva
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post #34 of 50 Old May 29th, 2012, 1:29 pm
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Re: What are the suspected reasons for final drive failures

Quote:
Originally Posted by New2rt
I couldn't possible tell you how many front wheel drive bearings I replaced, there has been that many.
It's far from the same thing as a single sided swing arm.

I know it's not the same thing. I also have replaced them. But not very many based on the numbers that are out there that never need replacing.

It's similarity is that it is supported on only one side. And it works fine.
You are not suggesting they should use a double support on those, are you?
My comment wasn't directed at you. It was directed at those who say "the problem is the single side arm."
dc
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post #35 of 50 Old May 29th, 2012, 2:03 pm
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Re: What are the suspected reasons for final drive failures

Quote:
Originally Posted by PadG
See the contradiction in your statement that I'd highlighted? The crown gear is not loaded against the pinion. I cannot be. A certain gap is required, and that is controlled by the relative position of the taper bearing's inner race on the aluminum half-shaft. BTW, do keep in mind that the ball bearing has a radial preload as well.
It's in response to this "The largest axial load on the assembly comes from the thrust of the worm gear onto the crown gear"

Then my response to this is "if what you say is true it will unload the taper roller bearing, not the ball bearing"

And yes you shim the ball bearing to preload the taper bearing but it does it using the ball bearing.

"A certain gap is required, and that is controlled by the relative position of the taper bearing's inner race" Yes backlash, I'd have to check if they shim inner or outer race.
I know you need this backlash, my response was to the article, I believe he said the crown gear is loaded against the pinion gear, I'll have to actually read it this time to be sure.

Not seeing the contradiction but I will focus on the article and what has been written and report back.

Yes I do believe over shimming is the main cause of bearing failure but I don't believe the preload is there to cancel worm gear thrust it's there because they are using a tapper roller bearing.
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post #36 of 50 Old May 29th, 2012, 4:55 pm
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Re: What are the suspected reasons for final drive failures

The bearing preload on any spiral bevel assembly is there to prevent gear misalignment under the designed transmissible forces for that arrangement. In other words, the crown gear (technically the bevel gear) is held sufficiently rigid so the transmitted torque does not change the gear mesh quality. Backlash is not left-over clearance or anything like that, it is designed into the gear set to allow for set-up, expansion, lubrication and silent operation when at operating temperature. Backlash must be set in a range while not compromising the contact pattern on the gear teeth, otherwise the drive will operate noisily and lubrication of the gear teeth will be compromised, so shortening the life of the gear set. Bevel gear arrangements are among the most technically challenging to set up (correctly), that's why they need to be well understood, because there is adjustment possible in 2 planes. Hope this helps rather than confuses.

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post #37 of 50 Old May 29th, 2012, 8:30 pm
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Re: What are the suspected reasons for final drive failures

OK, I read the information in the link provided by CharlieVT and I stick by my posts.

I saw nothing to indicate the majority of the axial load is caused by pinion thrust.
Preload is preload no matter which bearing you shim. It will spread the load between the two. With this design it makes sense to shim the ball bearing to achieve this. You could shim the taper bearing but it would require more work and rechecking of backlash. With this design you can't have preload on one and not the other.

The preload keeps the taper bearing centered, if not you would have run out. Do away with the taper bearing do away with preload. I'll stick with the preload is there because of the taper bearing.

It makes sense to me why the ball fails if the preload is excessive rather thean the taper

A final note as far as needle bearings can't resist axial loads, it depends on the orientation. They do make needle thrust bearings.
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post #38 of 50 Old May 30th, 2012, 7:00 am
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Re: What are the suspected reasons for final drive failures

Entertaining reading, watching things get batted back and forth.
I suspect you are both correct in elements of what you are saying.

Sometimes and answer is "All of the above."

It is pretty easy to understand the forces in a gearbox when everything is static. In the our FD the preload stabilizes the tapered roller bearing through the deep groove crownwheel ball bearing. Therefore the preload is also stabilizing the crownwheel bearing. Being a class "C" (sloppy bearing), without some axial preload the crownwheel bearing would be unstable. Additionally, this preload in stabilizing the crowngear assembly, stabilizes the relationship between the crowngear and pinion gear. The gear tooth contact pattern and gear lash are established by a shim in the input pinion shaft area and a shim under the tapered roller bearing, respectively.

When static, all the axial force on the crowngear assembly is from the preload.
When drive line acceleration (not constant velocity, but acceleration, or deceleration) is applied, additional forces will be applied to the crowngear assembly from the input pinion gear.

An engineer's analysis would reveal multiple vectors of force, but one of those vectors is certainly going to be axial to the crowngear assembly and in the direction of increasing compressive force on the crownwheel bearing, i.e. the same axis being applied by the preload but in the opposite direction. How much addtitional axial force would be applied on the crownwheel bearing during acceleration? Answer: how hard are you going to hit the throttle? It seems to me that a very aggressive acceleration would apply a significant axial force on the crownwheel bearing; a force that could easily exceed the static preload force. I suspect that this is what Dennis is referring to.

This axial force applied to the crowngear assembly on acceleration/deceleration will tend to unseat (unload) the tapered roller bearing. The preload needs to resist this unloading to the point that the tapered roller bearing remains stable. The crownwheel bearing sits between the axial force of the preload and the opposite axial force of acceleration.

Add to the static force of preload, and the dynamic force of acceleration the additional forces of pounding down the potholed roads of Vermont, two up, with the bike loaded to maximum with camping gear, and the dynamic forces on the whole FD assembly are indeed complex.

When we get past all this arcane information, the shimming needs to be correct so that there aren't damaging forces applied to components (the crownwheel bearing being the one that fails if the crownwheel assembly preload is excessive) and there is a lubrication space between parts that move with respect to each other.

I'll say again, I believe the engineers at BMW did a decent job of designing the K1200LT FD, and that manufacturing (machining) of components and assembly of those components have lead to multiple types of failures. The most common of those failures, the "classic" crownwheel bearing failure is the result of assembly error, i.e. excess preload shim thickness.

That bearing is in a pretty harsh environment: acceleration and deceleration forces, road surface and pothole pounding, etc. Add to that excess preload, the bearing surface gets spalled, the contacting surfaces are deprived of lubricant, and the bearing cries "Uncle!".
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post #39 of 50 Old May 30th, 2012, 7:18 am
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Re: What are the suspected reasons for final drive failures

I must admit I understand less than 1/2 of what you guys are talking about, but I sure do like reading it. Thanks for caring!

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post #40 of 50 Old May 30th, 2012, 8:56 am
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Re: What are the suspected reasons for final drive failures

OK, I am backing out now. I have had enough discussions on the topic from the past, and really don't want to rehash them again. Curtis has a good understanding, and that is enough for me!

Pad. Gajajiva
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post #41 of 50 Old May 30th, 2012, 9:49 am
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Re: What are the suspected reasons for final drive failures

+1 on Curtis's explanation.

What isn't obvious to many is that gears not only need to have the right profile, they need to have VERY precise centers of rotation or they will make a lot of noise. The loading is complex for the FD axle as not only does it have to react tire loads, it also has to react the gear loads. The gear loads include thrust and separation from the pressure angle of the teeth, the spiral nature of the teeth, all from the transmitted torque.

Preload is necessary for the precision necessary for quiet gear sets. Fortunately the transmitted torque is highest only at very low speeds where gear noise can be tolerated, and preload can be exceeded.

I suspect that the FD engineering job was a SOB at BMW that has been confounded by marginal assembly quality control.

What I'd like to know is where has the 4% failure rate come from. I'm guessing it is more like half. I don't know of any higher mileage local FDs that haven't failed.
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post #42 of 50 Old May 30th, 2012, 10:03 am
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Re: What are the suspected reasons for final drive failures

Quote:
Originally Posted by PadG
OK, I am backing out now. I have had enough discussions on the topic from the past, and really don't want to rehash them again. Curtis has a good understanding, and that is enough for me!
Padej,
Thanks for all your contributions. I have read your past posts with interest and appreciation. Yeah, sometimes the discussion becomes a little argumentative; interesting dynamic, this online discourse thing....

I have always tried to eventually bring the online discourse back to the ultimate search for truth regarding Final Drive failures. Analagous to the scientific process where a theory is proposed and then subjected to tests in an effort to disprove the theory, online discussion (debate) is a process wherein ideas are presented and then challenged.

However, in this forum, anyone, regardless of credentials, can contribute. No referreed journals here. So becomes the challenge to "separate the wheat from the chaff". I come to this party with a scientific background and significant "shade tree mechanic" experience. (Meaning I've a professional scientific academic background and I've stripped a hell of a lot of bolts in my lifetime.) I look at poster's profile to see what they tell us about themselves and I read their posts for content and construction. (Yes, grammer counts. A poster who shoots from the hip and ignores typos, etc. gets less credibility). I estimate the value and veracity of those posts and add information to my FD "database" based on a subjective assessment of those posts.

Yeah, the discussion is repeative and reduntant over time.
(The statement: "repeative and redundant" was brought to you by the department of redundancy department, which brought you this statement.)

It can become tedious, and I have vowed to quit posting on the subject of FDs on many occasions. But, I frequent this board, and when I find a misinformed statement, or question regarding FD failures, I can't help myself and find myself posting on the subject again. (It helps to be retired.)
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post #43 of 50 Old May 30th, 2012, 10:11 am
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Re: What are the suspected reasons for final drive failures

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Originally Posted by CharlieVT
It can become tedious, and I have vowed to quit posting on the subject of FDs on many occasions. But, I frequent this board, and when I find a misinformed statement, or question regarding FD failures, I can't help myself and find myself posting on the subject again. (It helps to be retired.)
... and we are all, well most of us, the better for it, Curtis.

I hope you never find the ability to "help [yourself]" stop posting. Your experience and wisdom would be sorely missed.

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post #44 of 50 Old May 30th, 2012, 10:37 am
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Re: What are the suspected reasons for final drive failures

Quote:
Originally Posted by niel_petersen
....I suspect that the FD engineering job was a SOB at BMW that has been confounded by marginal assembly quality control....
Niel,
I have always appreciated your posts. You've made significant contributions here.

What I have selected from your post and quoted above is an interesting element of the "classic" crownwheel bearing failure.
To what extent are the engineers responsible for making the assembly of their creation easy for those on the factory floor?

I have a theory as to how so many early final drives ended up being overshimmed by the factory, and I've alluded to this in previous posts and won't go into it in detail here. But, frankly, I don't see the assembly of final drive as all that complicated. Certainly, no more complicated that the transmission or the internal combustion engine. Maybe the assembly process or tools that were prescribed to the assemblymen was flawed (I suspect this is the case). But I do not think that the basic engineering of the final drive was flawed.

Having measured for preload shimming of many final drives using different methods of measurement, I have come to realize how easy it would be to come up with a measurement that resulted in excessive preload. It is related to the fact the bearing is class "C" where the inner race and outer race are "sloppy" with respect to each other. In measuring, you have to be very careful that you don't "tilt" the outer race.
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post #45 of 50 Old May 30th, 2012, 12:18 pm
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Re: What are the suspected reasons for final drive failures

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It is related to the fact the bearing is class "C" where the inner race and outer race are "sloppy" with respect to each other. In measuring, you have to be very careful that you don't "tilt" the outer race.
My guess is that is probably what has happened at BMW. What I can't figure out is why they didn't get on top of the problem sooner - or even have they yet?
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post #46 of 50 Old May 30th, 2012, 2:33 pm
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Re: What are the suspected reasons for final drive failures

Quote:
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Padej,
Thanks for all your contributions. I have read your past posts with interest and appreciation. Yeah, sometimes the discussion becomes a little argumentative; interesting dynamic, this online discourse thing....

I have always tried to eventually bring the online discourse back to the ultimate search for truth regarding Final Drive failures. Analagous to the scientific process where a theory is proposed and then subjected to tests in an effort to disprove the theory, online discussion (debate) is a process wherein ideas are presented and then challenged.

However, in this forum, anyone, regardless of credentials, can contribute. No referreed journals here. So becomes the challenge to "separate the wheat from the chaff". I come to this party with a scientific background and significant "shade tree mechanic" experience. (Meaning I've a professional scientific academic background and I've stripped a hell of a lot of bolts in my lifetime.) I look at poster's profile to see what they tell us about themselves and I read their posts for content and construction. (Yes, grammer counts. A poster who shoots from the hip and ignores typos, etc. gets less credibility). I estimate the value and veracity of those posts and add information to my FD "database" based on a subjective assessment of those posts.

Yeah, the discussion is repeative and reduntant over time.
(The statement: "repeative and redundant" was brought to you by the department of redundancy department, which brought you this statement.)

It can become tedious, and I have vowed to quit posting on the subject of FDs on many occasions. But, I frequent this board, and when I find a misinformed statement, or question regarding FD failures, I can't help myself and find myself posting on the subject again. (It helps to be retired.)

I never looked at a profile or put a whole lot on the use of grammar by posters.
What you do as a hobby or "shade Tree" I did professionally. 20 years 3 master certifications from 3 manufacturers. My job for the last 11 years is correcting the mistakes of engineers. There's my profile.

I didn't see anything as argumentative just a conversation.
Some don't like to be challenged, some don't mind.
I've read many of your posts regarding your rebuild process, good but not ideal.

Yes I know this group tends to circle the wagons around the old faithful but sometimes it doesn't hurt to open the gate.
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post #47 of 50 Old May 30th, 2012, 5:13 pm
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Re: What are the suspected reasons for final drive failures

Just thought I'd attach a couple of pics of a small bevel pinion from 1 of our gearboxes. The pinion shaft weighs 600 Kg and the gearbox input power is 2100kW. It runs 24/7, input shaft speed is 990 rpm. We have on-line vibration monitoring and do 3 monthly oil analysis. In some respects, setting these up is easier than our K12 FD's because of the size, but 1 thing does not change - the required accuracy.
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Dennis
1987 Yamaha TY250R
1991 Aprilia Climber 280
1988 K100RT (the pack horse)
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post #48 of 50 Old May 30th, 2012, 7:35 pm
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Re: What are the suspected reasons for final drive failures

Nice pattern - A healthy box!

My last go around was a 4 square automotive test stand which had a pair of 6000 rpm, ~30,000 in lbs but limited to ~400 hp on two 1:1 10 inch dia gear boxes with a spinning hydraulic actuator inside one gear of each box to provide the windup torque. Learned a lot from that one.....
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post #49 of 50 Old May 31st, 2012, 11:16 am
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Re: What are the suspected reasons for final drive failures

Quote:
Originally Posted by K100Dennis
The pinion shaft weighs 600 Kg
What machine is this pinion shaft from? I don't know of a bike that weighs 600Kg.

1996 Kinetic Pride 75cc - First motorized cycle at age 16.
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post #50 of 50 Old May 31st, 2012, 7:02 pm
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Re: What are the suspected reasons for final drive failures

Flender gearbox, model KMP500, overall assembled weight 79 tonnes, 1600 litres of gear oil pumped around at 400 litres/minute. Replacement cost $1.7M AU. It powers a vertical roller mill in our plant. Nice piece of kit, but it too, had an original design problem with the bearing spacer between the pinion shaft bearings. Nice work rebuilding it though. Running happily now. 33 years in industry and I still see new failurs and design problems, makes for an interesting job, shame it takes up so much leisure time which could be spent burning fuel and wearing out tyres.

Dennis
1987 Yamaha TY250R
1991 Aprilia Climber 280
1988 K100RT (the pack horse)
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