Mech Engners- Final Drve DeMagnizng Question - BMW Luxury Touring Community
 
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post #1 of 15 Old Jun 2nd, 2009, 8:15 am Thread Starter
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Question Mech Engners- Final Drve DeMagnizng Question

I was gifted a demagnitizer by Saddleman who made the trip from NC to VT for our annual Ride Vermont weekend. (Saddleman is a real gent who knows how to cover the miles on his LT, he got the longest distance traveled award for his participation in RideVT2009).

He is a professional builder of NASCAR engines and gave me a field meter and demagnitizer for demagnitizing machine parts. Interesting concept I had not been exposed to before.

From now on I will test failed bearings for magnetic field using the field meter, and will check and demagnitize new bearings when assembling drives. In the words of Saddleman, checking the field and demagnetizing the crown wheel bearing if needed before assembly "can't hurt".

Here is the concept as I understand it: If the races and balls of the bearing are magnetized, some of the small metal particles that are normally generated when a new gear assembly is breaking in will stick to the balls and races instead of settling onto the drain plug magnet. These little metal particles contribute to the spalling of the balls and races that ultimately results in stress to the bearing retainer and the subsequent failure that some know all too well.

From reading bearing sites, I find that some manufacturers of small precision bearings are very clear on the need for meticulous handling of the bearing during installation, including degaussing the bearing before assembly.

I don't recall this subject being brought up before in posts speculating on causes of crown wheel bearing failure. What is the possibility that some crown wheel bearing got exposed to a magnetic field and were left magnetized? And could that be contributing factor to final drive failures?
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post #2 of 15 Old Jun 2nd, 2009, 12:21 pm
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Re: Mech Engners- Final Drve DeMagnizng Question

Wow, That's really out there. Unfotrunately it also makes sense.

You can certainly magnetize steel so I guess it's not so far out as one would initially think.

I suppose it wouldn't take too much metal adhering to a roller bearing to cause issues.

Interesting concept...I'll have to take that into consideration for future work..

Have degausser will degauss.


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post #3 of 15 Old Jun 2nd, 2009, 2:08 pm
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Re: Mech Engners- Final Drve DeMagnizng Question

I have not heard of the possible benefit for degaussing bearings. The forces involved in crunching fine steel in the races would seem to be orders of magnitude greater than could be generated by even a strong magnet.

There is a lot of precedence for magnetic drain plugs etc, but these should be located at the lowest points in fairly stagnant oil. Our FDs probably don't have much stagnant oil. Rare earth magnets (such as are found in a hard drive) would be even better to attract steel.

Of course steel will slowly self-magnetize in the presence of earth's magnetic field - don't park your bike the same way all the time..............!.

It would be interesting though to try taking a small compass to a failed bearing to see if there is a field contribution from a bearing race. For certain degaussing isn't going to hurt and it is quickly done.
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post #4 of 15 Old Jun 2nd, 2009, 8:07 pm
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Re: Mech Engners- Final Drve DeMagnizng Question

Very cool stuff.................



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post #5 of 15 Old Jun 20th, 2009, 2:54 pm
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Re: Mech Engners- Final Drve DeMagnizng Question

Curtis

Magnetized bearings can definitely lead to premature failure if metallic particles are present, however it is very unlikely that new bearings are magnetized.
If an induction heater is used to heat a bearing for installation - it will cause the bearing to become magnetized - unless the industion heater includes a demagnetizer. http://www.mapro.skf.com/pub/publ/MP3206E.pdf
I'm a big believer in changing the oil in new rear drives and tranmisssions within the first few hundred miles to get rid of these initial wear particles asap and reduce the risk of bearing damage.
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post #6 of 15 Old Jun 20th, 2009, 5:17 pm
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Re: Mech Engners- Final Drve DeMagnizng Question

Yep me too! Changed FD myself at 300 miles, dealer changed it at the 600, with motor and tranny. I carried my own FD and Tranny fluid in, let him make it on the engine oil.

If we did any motor/head work on our HD we always change from 50 to 100 miles to flush it.

This still is a very interesting concept for sure.

I know we always washed bearings with what they we going to be bathed in before final assembly.

Quote:
Originally Posted by RealWing
Curtis

Magnetized bearings can definitely lead to premature failure if metallic particles are present, however it is very unlikely that new bearings are magnetized.
If an induction heater is used to heat a bearing for installation - it will cause the bearing to become magnetized - unless the industion heater includes a demagnetizer. http://www.mapro.skf.com/pub/publ/MP3206E.pdf
I'm a big believer in changing the oil in new rear drives and tranmisssions within the first few hundred miles to get rid of these initial wear particles asap and reduce the risk of bearing damage.
Jim

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post #7 of 15 Old Jun 20th, 2009, 8:06 pm
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Re: Mech Engners- Final Drve DeMagnizng Question

You would be surprized at how many new parts are magnetized. All it takes is a electromagnet picking up a roll of steel. On a splash fed unit such as a trans. or FD every time you stop the oil drains slowly down to the bottom over bearings & gears. The only place you would want a magnet is at the very bottom. A drain plug.

I have had parts that 125psi of air would not blow off the little metal fuzz until it was demagnetized. All I know is that it certainly can do no harm to demagnetize all engine,transmission & final drive parts. Thats just something extra we do at the race shop.

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post #8 of 15 Old Jun 21st, 2009, 6:05 am Thread Starter
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Re: Mech Engners- Final Drve DeMagnizng Question

Hi Dave,
I tested a couple of failed bearing races with the field meter you gave me. They both caused a little needle movement, but not much. I also tested a used, good bearing from a preemptive FD rebuild and there was enough field to cause a little needle movement.
So my conclusion: there is a small magnetic field assoicated with some crownwheel bearings. How significant this is to failure of these bearings can only be a matter of speculation, BUT as you point out demagnetizing them is easy and can't hurt.

I did some online reading of bearing manufacturer sites and found that some manufacturers are very specific about demagnitizing as part of assembly procedure. This was especially true when talking about small precision bearings, but it makes sense that it is applicable to larger bearings as well.
So degaussing these bearings makes sense to me, and it is certianly easy to do If You Have the Tool. THANK YOU!

So what's the status of your bike? All the participants of Ride Vermont 09 where impressed with your coolness under fire, misbehaving bike so far from home, and a limited schedule, and all. And we were all relieved to learn you managed to limp home. Is the bike fixed? What turned out to be the problem?

Best Regards from the Deep South of Vermont,



Quote:
Originally Posted by saddle-man
You would be surprized at how many new parts are magnetized. All it takes is a electromagnet picking up a roll of steel. On a splash fed unit such as a trans. or FD every time you stop the oil drains slowly down to the bottom over bearings & gears. The only place you would want a magnet is at the very bottom. A drain plug.

I have had parts that 125psi of air would not blow off the little metal fuzz until it was demagnetized. All I know is that it certainly can do no harm to demagnetize all engine,transmission & final drive parts. Thats just something extra we do at the race shop.
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post #9 of 15 Old Jun 21st, 2009, 9:32 am
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Re: Mech Engners- Final Drve DeMagnizng Question

Demagnetizing ? I have a few Question?When I rebuilt my final drive I used a induction bearing heater which I use at my job where I rebuild electric motors ranging from 1/3 to 500 horse power motors with speeds from 500 to 3600 rpm.Now this is the recommended method by the bearing manufacturers to heat bearings.The whole time you are heating the bearing you are inducing a field through the bearing which of coarse causes a magnetic field and some of that is residual .Magnetizing is very easy to come by with harden steel that the bearing is made of and add the fact that the bearing is spinning and some of this is natural. Another way magnetizing happens in steel is by cold forming the simple method of hitting steel with a hammer will cause magnetizing.It all seems to make since and what your saying sound dead on to me.The question is how do you prevent it over the life time of the bearing.
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post #10 of 15 Old Jun 21st, 2009, 10:42 am
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Re: Mech Engners- Final Drve DeMagnizng Question

Quote:
Originally Posted by CharlieVT
Hi Dave,
I tested a couple of failed bearing races with the field meter you gave me. They both caused a little needle movement, but not much. I also tested a used, good bearing from a preemptive FD rebuild and there was enough field to cause a little needle movement.
So my conclusion: there is a small magnetic field assoicated with some crownwheel bearings. How significant this is to failure of these bearings can only be a matter of speculation, BUT as you point out demagnetizing them is easy and can't hurt.
,
Not exactly Anova testing

http://www.physics.csbsju.edu/stats/anova.html

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post #11 of 15 Old Jun 21st, 2009, 11:22 am Thread Starter
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Re: Mech Engners- Final Drve DeMagnizng Question

Quote:
Originally Posted by Yamadog
Let's see... I made this statement: ".....So my conclusion: there is a small magnetic field assoicated with some crownwheel bearings. How significant this is to failure of these bearings can only be a matter of speculation, BUT as you point out demagnetizing them is easy and can't hurt.", and you responded with the above post.

Well, I do have an education which includes advanced statistics. I can read your link and understand it; I am familiar with the terms.

After an understanding of "t", ANOVA, etc. I still find that the most salient quote regarding stastics is: "Statistics don't lie, but liers use stastitics." Second to that is: "if you can't dazzle 'em with brilliance, baffle 'em with bullsht" comes to mind.

If you read my statement, you saw such qualifers as "some" and "speculation". No where did I suggest that there has been a demonstrated causal link between magnetized bearings and FD failure. And I certainly didn't pose an hypothesis with data that could be meaningfully analyzed by statistical analysis. Frankly, I am pretty careful not to do that.

What exactly is the point of your statement: "Not exactly Anova testing." ?

Clearly no one has generated enough data to demonstrate a clear causal link regarding FD failures; never mind statistical significance. The cause of FD failures is a matter of speculation. I have simply tried, with the help of members of this board, to understand and shed some light on what factors may be contributing to FD failures. Many thoughtful and knowledge people have posted and contributed to our understanding of what may be making these drives fail. Professional mechanics and mechanical engineers both have weighed in with good observations, suggestions, and information. I regard their contributions to our understanding of FD failures as efforts worth emulating.

Last edited by CharlieVT; Jun 21st, 2009 at 2:58 pm.
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post #12 of 15 Old Jun 21st, 2009, 4:24 pm
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Re: Mech Engners- Final Drve DeMagnizng Question

Thanks for your contributions and effort Charlie, very much appreciated by most of us. Interesting the concept of demagnitization. And, always learning something...

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post #13 of 15 Old Jun 22nd, 2009, 7:38 am
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Re: Mech Engners- Final Drve DeMagnizng Question

Quote:
Originally Posted by CharlieVT

What exactly is the point of your statement: "Not exactly Anova testing." ?
Sorry you were offended Charlie. To answer your question: The point is, this "speculation" of yours is no more valid than a random value. This is no indictment of you, your education, your value as a forum contributor or (and especially) your ideas and interest towards our common goal of understanding our machines. In fact, I'm sure you know more about the K1200LT final drive than I do...how's that for speculation?

Maybe a little more riding (and less speculating) would help

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post #14 of 15 Old Jun 22nd, 2009, 1:17 pm
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Re: Mech Engners- Final Drve DeMagnizng Question

Geez - I retired as a MechEngr from the fatigue testing business seven tears ago & I never heard of it.
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post #15 of 15 Old Jun 22nd, 2009, 1:36 pm
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Re: Mech Engners- Final Drve DeMagnizng Question

Quote:
Originally Posted by CharlieVT
What is the possibility that some crown wheel bearing got exposed to a magnetic field and were left magnetized?
Thats why all my final drives wear a little tinfoil hat. You can never be too careful out there . . .

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