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Discussion Starter #1
Looking for a reason for failure.

2005 K1200LT at 36,000 miles had rear end torn down, rear end smaller bearing race had spun on shaft. I believe the inner race to shaft is to be a slight interference fit and the tapered bearing showed no evidence of damage or lack of lubrication.

Is this a case of latent defect from manufacturing/assembly?

Or is there an engineering explanation for this outcome? I am at a loss to determine a cause.

See attached Photo 1 showing shaft damage
Photo 2 showing bearing in place loose on shaft
 

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Yup, machining defect. Not the most common form of KLT final drive failure, but known to occur. Others have reported this failure mode, seems like the year 2005 was the year for this failure. (Earlier bikes more commonly had crownwheel bearing failure, and tapered roller bearing was fine.)

Shaft/seat for tapered roller bearing apparently machined too small resulting in spun bearing. I have rebuilt one final drive with Locktite 600 (this was not a failed final drive, but rather one where I found the bearing to be loose during an inspection).

The pic you posted shows the shaft/seat not looking too bad. I'd consider rebuilding that drive with loctite 660 and using it as a spare final drive. A better rebuild would involve replacing the crown wheel assembly.... but when you evaluate the cost, getting a whole new final drive may make sense.
Here's the Loctite product engineered for this kind of application:
http://www.useloctite.com/products/product_details_retaining.asp?cat=Machinery Repair

More final drive rebuilding info here:
http://www.bmwlt.com/uploads/lt_final_drive_rebuild.wmv

Thanks for posting your photos and description of your failure.



DLundberg said:
Looking for a reason for failure.

2005 K1200LT at 36,000 miles had rear end torn down, rear end smaller bearing race had spun on shaft. I believe the inner race to shaft is to be a slight interference fit and the tapered bearing showed no evidence of damage or lack of lubrication.

Is this a case of latent defect from manufacturing/assembly?

Or is there an engineering explanation for this outcome? I am at a loss to determine a cause.

See attached Photo 1 showing shaft damage
Photo 2 showing bearing in place loose on shaft
 

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Discussion Starter #3
Thanks Charlie
Wonderful video I just finished watching it.

Yes your suggestion looks like the way to go. You are right by the time both the pinyon gear and drive gear (set) and bearings, shims etc with labor the price is with in $100 of a new unit with labor to instal.

I am very tempted by the locktite solution even at this stage.
 

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Hello DLundberg

If the shaft is not too bad I would take it to a machine shop and have it knurled , that will raise up enough metal to take up a couple thousands slop .

Bob G
 

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DLundberg said:
Looking for a reason for failure. ....
What were the symptoms of that particular failure? What prompted you to open the drive?
 

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Discussion Starter #8
The bike went in for its 36,000 mile service. The service tech said the rear wheel had side to side play while on the lift. So I authorized the tear down to determine the problem. As a side note the head shake at 42 mph has been getting worse. It will be interesting to see if the head shake goes away after the rear end is repaired.
 

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Grinding an external diameter undersize for a pressed-on bearing is just lousy manufacturing quality control. This isn't rocket science. It should have been caught at the grind stage, and then again at the assembly stage.

A Russian emigre' friend noted that in the bad old Commie days, such scrap was always saved for future "spare parts". Was something even worse going on at BMW?

I'm starting to change my mind on FD failure reasons. Maybe it is just poor BMW quality.

You could try the Locktite but that doesn't give the pressed-on effect to retain the inner race with the shaft, and there will eventually be rotation between the two. I'd be inclined to try a stainless or even aluminum foil shim sleeve and heat/shrink the two together using an oven (250 degF) and some liquid nitrogen (~-350 degF) I think you can get shim stock down to about .0015" or even .0010" thickness.

MN Engr (retired)
 

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niel_petersen said:
Grinding an external diameter undersize for a pressed-on bearing is just lousy manufacturing quality control. This isn't rocket science. It should have been caught at the grind stage, and then again at the assembly stage.....I'm starting to change my mind on FD failure reasons. Maybe it is just poor BMW quality....
Yeah, that's my vote. Improper external dimenensions have been reported for the crownwheel bearing seat, the tapered roller bearing seat, and for the crownwheel assembly itself where the crownwheel gear (steel) is pressed onto the crownwheel shaft (aluminum) (reported in BMWON). That constitutes ALL THREE machined external diameters on the crown wheel aluminum piece. I think that former Soviet Block East Germans, now working for BMW (Google the managment problems that West Germany has had after reunification) have been working the machining/assembly line at BMW. The final drive failures can be attributed to the sloppy work and poor work ethic of workers of that background. (Just my opinionated opinion ;) )
 

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CharlieVT said:
Yeah, that's my vote. Improper external dimenensions have been reported for the crownwheel bearing seat, the tapered roller bearing seat, and for the crownwheel assembly itself where the crownwheel gear (steel) is pressed onto the crownwheel shaft (aluminum) (reported in BMWON). That constitutes ALL THREE machined external diameters on the crown wheel aluminum piece. I think that former Soviet Block East Germans, now working for BMW (Google the managment problems that West Germany has had after reunification) have been working the machining/assembly line at BMW. The final drive failures can be attributed to the sloppy work and poor work ethic of workers of that background. (Just my opinionated opinion ;) )
:rotf:

McCarthy was RIGHT after all! :D

It WAS a communist plot! ;)
 

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As for the Locktite fix? I know at the machine shop at Delta airlines they use a plasma spray to build up engine parts that have been worn beyond limits. The plasma spray is very durable and can be built up then machined back down to the proper specs. I don't know if this kind of process is available to the average Joe, but it may be something worth looking into.

Whatever you decide, I hope your new/rebuilt final drive lasts you a good long time and you can recapture the joy of riding your LT.
 

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Plasma spray would work, or even hard chrome plate the diameter and grind to proper size, depending on how undersize it is.
 

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Call me crazy and I'm not sure that I would trust it or that it would work but what about aluminum foil tape? No not duct tape but the actual aluminum foil tape that's used in duct work A wrap or two then shrink fit using the oven and freezer method.
 

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Knurl the shaft, use the Loctite when you mount it and hope like hell you never have to take it apart because that stuff works as advertised. Anyway it did on my old Mustang brake hub where the outer bearing race spun.
 

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niel_petersen said:
Grinding an external diameter undersize for a pressed-on bearing is just lousy manufacturing quality control. This isn't rocket science. It should have been caught at the grind stage, and then again at the assembly stage.

A Russian emigre' friend noted that in the bad old Commie days, such scrap was always saved for future "spare parts". Was something even worse going on at BMW?

I'm starting to change my mind on FD failure reasons. Maybe it is just poor BMW quality.

You could try the Locktite but that doesn't give the pressed-on effect to retain the inner race with the shaft, and there will eventually be rotation between the two. I'd be inclined to try a stainless or even aluminum foil shim sleeve and heat/shrink the two together using an oven (250 degF) and some liquid nitrogen (~-350 degF) I think you can get shim stock down to about .0015" or even .0010" thickness.

MN Engr (retired)

+1

FD would never meet six sigma. I would love to get my hands on the design calcs and tolerances of this FD.
 

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By the looks of the contact patern on the coast side of the ring gear, it's gonna be noisy!
The bad bearing allowed the pattern to move, wearing a different pattern on the teeth.
 
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