FD Gear oil analysis - BMW Luxury Touring Community
 
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post #1 of 9 Old Oct 11th, 2012, 11:07 pm Thread Starter
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FD Gear oil analysis

Recently I changed the FD oil and sent a sample off for analysis (Castrol 75W90). Results returned a reading of 69 ppm for Fe (Iron). When the megnetic plug was inspected at the time it had nothing except the "fuzz" on it, but when I left some oil in another clear plastic sample bottle, after standing for a week or so there appeared to be dark deposits suspended throughout the oil. So I took a very strong magnet and taped it to the side of the sample bottle, waited for approximately 2 hours to check and guess what ?...... the oil was crystal clear with all the fuzz over at the magnet. So the fuzz is not aluminium, it is iron based (magnetic) which means of course it must be from gear surfaces or bearings. I have just completed 10,000 Km's in the last month and dropped out the FD oil again. It came out darker than the previous sample which had done 3000 Km's. Sent off a sample to the lab, still awaiting the results, but I have repeated the magnet test and again the oil has cleared off but this time there is a larger amount of fuzz to the side of the bottle (same size bottle and sample volume). I believe I may have discovered a very early failing of the crown bearing and am now tempted to open the FD casing to see what shims exist. I have no measureable wheel movement, no oil leakage, smooth rotation and a new FAG 61917 c3 bearing in my tool box. Thoughts please gentlemen ?

Dennis
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post #2 of 9 Old Oct 11th, 2012, 11:51 pm
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Re: FD Gear oil analysis

Place the magnetic drain plug in a cup and fill it with mineral spirits paint thinner. Any thick oil will dissolve and you can see more clearly the iron fragments. Bottom line is if you have have visible (shiny) fragments, it's on the way out. I caught mine early using a chip detector I built. It was over-shimmed by .20mm. I bet yours is too.


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post #3 of 9 Old Oct 12th, 2012, 12:58 am
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Re: FD Gear oil analysis

I caught a deteriorating ball and the race delaminating by simply looking for shiny flakes.
After taking the drive off and inspecting the bearing there was only one ball that was crazing
and cracking and just a few small spots on the inner and outer race where metal was starting
to release. Of course this all showed up in the oil and very visible to the naked eye. I seem
to recall that heavy fuzz was a precursor to the bearing failure.

At the stage you are at you will not be able to feel wheel wobble nor will any roughness or
noise come from your drive while mounted on the bike. In the manner that this bearing is
mounted significant damage to the bearing and cage will need to occur for these symptoms to occur.

In my opinion your analysis is a little more scientific but you will not need to replace the
bearing until the shiny flakes are upon you.

BTW, my drive had two shims - took out the thinner of the two, replaced the bearing and
dropped the drive back in the bike. Took off for CCR 20011 in Boise, ID. The bike was a
2002 with 58,000 miles.

When I go back from the trip out west I was not satisfied with the temporary fix of just taking
out the thinner of the two shims so I did another bearing replacement and a much more
through cleaning of the drive. Here is a video shot showing a portion of my bearing
replacement and measuring to determine the proper shims I would need for the rebuild.

http://www.bmwlt.com/forums/showpost...5&postcount=28

Good luck in your next steps . . .

Dan Finazzo
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post #4 of 9 Old Oct 12th, 2012, 2:30 am
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Re: FD Gear oil analysis

thanks for the videos Dan... getting a sense of what is going on now.
so much simpler with visual clues than just reading posts.
cheers

Chris
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post #5 of 9 Old Oct 12th, 2012, 7:48 am
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Re: FD Gear oil analysis

Increasing amounts of "fuzz" may well be an indication of early crownwheel bearing failure. I have done a number of preemptive FD rebuilds where the owner noted increasing magnetic fuzz and on inspection of the bearing, wear of the races was present. Note well that some of these bearings did not have spalling/pitting, but rather a wallowing out of the races. Some of my findings were written up here: http://www.bmwlt.com/forums/showthread.php?t=63109

Repeat oil analysis over time would give earlier warning than visual evaluation of fuzz in the lube, but both are an indication of the same thing. i.e. carbon steel parts shedding increasing amounts of metal indicating something wearing out, in this case most likely the crown wheel bearing.

Opening "the FD casing to see what shims exist" won't tell you anything unless you compare the existing shims to shim thickness calculated for a new bearing. That comparison would provide another data point regarding suspected cause of premature crownwheel bearing failure. that is, excess preload.


Outward signs like: "measureable wheel movement, no oil leakage, smooth rotation" have never been reported as indicators of early crownwheel bearing failure. As a matter of fact, even a worn bearing, removed from the final drive, and held in the hand will likely feel smooth on rotation. In my experience, the only way to really assess the status of a bearing is to cut it open for a direct view of the races. The wallowing out of the races that I have seen in early stages of bearing degradation are not obvious even on direct inspection unless other bearing races are available for comparison.

My suggestion is that since you have increasing fuzz, and increasing metal in lube as determined by oil analysis, and you already have a bearing in hand, is to rebuild the final drive with your new bearing using proper technique, carefully measuring for preload of that bearing.
(Once you have done that, comparing your calculated shim thickness to the original shim thickness will give you an indication as to whether the original setup was over-shimmed, but again that is the only reason to be interested in what the original shim thickness is.)


Quote:
Originally Posted by K100Dennis
Recently I changed the FD oil and sent a sample off for analysis (Castrol 75W90). Results returned a reading of 69 ppm for Fe (Iron). When the megnetic plug was inspected at the time it had nothing except the "fuzz" on it, but when I left some oil in another clear plastic sample bottle, after standing for a week or so there appeared to be dark deposits suspended throughout the oil. So I took a very strong magnet and taped it to the side of the sample bottle, waited for approximately 2 hours to check and guess what ?...... the oil was crystal clear with all the fuzz over at the magnet. So the fuzz is not aluminium, it is iron based (magnetic) which means of course it must be from gear surfaces or bearings. I have just completed 10,000 Km's in the last month and dropped out the FD oil again. It came out darker than the previous sample which had done 3000 Km's. Sent off a sample to the lab, still awaiting the results, but I have repeated the magnet test and again the oil has cleared off but this time there is a larger amount of fuzz to the side of the bottle (same size bottle and sample volume). I believe I may have discovered a very early failing of the crown bearing and am now tempted to open the FD casing to see what shims exist. I have no measureable wheel movement, no oil leakage, smooth rotation and a new FAG 61917 c3 bearing in my tool box. Thoughts please gentlemen ?
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post #6 of 9 Old Oct 12th, 2012, 7:53 am Thread Starter
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Re: FD Gear oil analysis

Thanks Dan, yes I've read plenty about this issue, and discussed it with Curtis as well. I'm assuming there are 2 shims in the preload set-up for the crown bearing, usually a thicker one and the thin one for the fine adjustment. It does seem that most of the drives are over shimmed by about 0.15 to 0.2 mm. I too would be tempted to just remove a shim if it happened to be that thickness, based on most of the cases where that's what was found after proper set-up using the jig. A new seal as well of course. I don't think I'll be waiting too long to attack this, sooner rather than later.

Dennis
1987 Yamaha TY250R
1991 Aprilia Climber 280
1988 K100RT (the pack horse)
2005 K1200LTE Light yellow metallic
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post #7 of 9 Old Oct 12th, 2012, 8:19 am
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Re: FD Gear oil analysis

Dennis,

About 50% of final drives have two shims. Preload thickness is calcualted to the nearest 0.05mm. Rather than have twice as many shims in inventory, BMW supplies a range of shims at 0.10mm thickness intervals and one shim that is 0.15mm thick.

If preload calcualtions call for a thickness that is close to a multiple of 0.10mm a single shim is used. If calculations call for a thickness that is a multiple of 0.05mm then two shims will be used, one being the 0.15mm shim. One exception, BMW also reduced inventory requirements by leaving out a 0.50mm shim, requiring that a 0.20 and 0.30mm shim be used in combination for a 0.50mm thickness.

example:
If a 0.30mm shim thickness is called for then a single 0.30mm shim will be used.
If a 0.35mm shim thickness is called for then two shims would be used, a 0.20mm and a 0.15mm shim.

While I have reported that many failed crown wheel bearings were over shimmed by 1.5-0.20mm, many have also had more or less variation. While removing a 0.15mm shim during a failed bearing replacement might be a good approach when trying to get back on the road as soon as possible, I would not advocate that approach for a routine rebuild. If you're going to go to the trouble of replacing the bearing, it is worth the additional trouble to do the measurements and have greater confidence in the setup.

Quote:
Originally Posted by K100Dennis
Thanks Dan, yes I've read plenty about this issue, and discussed it with Curtis as well. I'm assuming there are 2 shims in the preload set-up for the crown bearing, usually a thicker one and the thin one for the fine adjustment. It does seem that most of the drives are over shimmed by about 0.15 to 0.2 mm. I too would be tempted to just remove a shim if it happened to be that thickness, based on most of the cases where that's what was found after proper set-up using the jig. A new seal as well of course. I don't think I'll be waiting too long to attack this, sooner rather than later.
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post #8 of 9 Old Oct 12th, 2012, 6:43 pm
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Re: FD Gear oil analysis

Is this also a product of BMW engineers under sizing the crown bearing or using the wrong bearing set-up, Curious
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post #9 of 9 Old Oct 13th, 2012, 8:07 pm Thread Starter
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Re: FD Gear oil analysis

Thanks for the details on the preload shim increments Curtis, I understand that logic. Yes, I intend to do a proper preload calculation for the new bearing. Sooner rather than later is my approach in order to reduce the time running contaminated lube through all other componenets within the FD unit, including seals, as the "fuzz' is not good to have around them. Interesting is the fact that the magnetic plug does not/will not attract the fuzz to any degree whereby the oil will be cleaned.

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