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Discussion Starter #1
In the last week I started noticing an increasing howling noise that I initially attributed to tires. I had 14K on them so I went ahead and mounted a new set - it was due. The noise didn't go away so I drained the FD to check the magnet. I found a pretty good amount of silver slurry with noticeable flecks in it. I went ahead and pulled the FD - much easier than I thought - and after watching the video I tore into it.

I apparently caught it in the very early stages - no visible deterioration of the bearing but I do feel some roughness when I spin it by hand.

Here are the vitals I measured using the Dial Indicator method :

Shim thickness = 0.85mm
Gap W/O shim = 0.20" or 0.508mm

Preload = 0.850-0.508 = 0.342mm :eek:

Preload Spec = 0.05mm to 0.10mm

My calculations show I should have a shim of 0.60mm

Now for the question - am I safe buying that shim or do I really need to measure with the new bearing? I am assuming the spec on the bearing thickness is very tight.
 

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Discussion Starter #2
Ok, on closer inspection under bright light I can see galling on some of the balls. This seems to fit the profile CharlieVT reports.
 

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Send a PM for CharlieVT to confirm in case he misses your thread - I believe that you are right: the bearings are very accurate, the shims take out tolerances in the housing castings.
 

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Hiya Ralph,

You lost a decimal place when you reported a gap of 0.20" but we get it; your conversion of 0.508mm makes sense.

I'd really like to see that bearing, cut it open and take pics or send it to me? Is the retainer intact? You caught it before an oil leak, right?

If you calculate a preload of 0.60mm and you had 0.85mm in there, you were overshimmed by 0.25mm. That is consistent with what I have seen in failed crownwheel bearings.

BTW did you have two shims or just one? For 0.85mm I'm thinking you must have had a 0.70mm and a 0.15mm shim, yes?

I agree with you that for your observed gap you should have a 0.60mm shim. You might be okay preordering one. OTOH you might find a little difference between your old bearing and the new one. I'll gamble with your money :), go for it and order the shim. If you get it right you'll save shipping or extra trip later to get a shim. A $13 gamble.

That is something I want to know too, will measuring the exiting bearing, which I understand is pretty much intact, give you a reliable measure for the new bearing? My assumption has been that you are correct, that the bearing specs are very tight; that's what the mech. engineers tell me. I'd like to know how yours works out.

Thanks for posting.




rcoolbaugh said:
In the last week I started noticing an increasing howling noise that I initially attributed to tires. I had 14K on them so I went ahead and mounted a new set - it was due. The noise didn't go away so I drained the FD to check the magnet. I found a pretty good amount of silver slurry with noticeable flecks in it. I went ahead and pulled the FD - much easier than I thought - and after watching the video I tore into it.

I apparently caught it in the very early stages - no visible deterioration of the bearing but I do feel some roughness when I spin it by hand.

Here are the vitals I measured using the Dial Indicator method :

Shim thickness = 0.85mm
Gap W/O shim = 0.20" or 0.508mm

Preload = 0.850-0.508 = 0.342mm :eek:

Preload Spec = 0.05mm to 0.10mm

My calculations show I should have a shim of 0.60mm

Now for the question - am I safe buying that shim or do I really need to measure with the new bearing? I am assuming the spec on the bearing thickness is very tight.
 

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I'm having a devil of a time getting my measurements, but it looks as though my current bearing should have been shimmed at .18 -. 22, or .2mm, but it's currently shimmed at .5.
 

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Discussion Starter #6
Yep, the gap was 0.020". I did catch it before an oil leak. It looks to be in the very early stages. I just re-measured the shim, it is 0.80 mm.

After I get the new bearing and measure it I would be happy to send this one to you. PM me with an address.

The video was VERY helpful in disassembling the drive. The most time consuming part was grinding down the jaws on my 3 jaw puller to fit under the bearing.
 

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rcoolbaugh said:
Yep, the gap was 0.020". I did catch it before an oil leak. It looks to be in the very early stages. I just re-measured the shim, it is 0.80 mm.

After I get the new bearing and measure it I would be happy to send this one to you. PM me with an address.

The video was VERY helpful in disassembling the drive. The most time consuming part was grinding down the jaws on my 3 jaw puller to fit under the bearing.
I just checked my inventory.... I've got 3 0.60mm shims. You can have one. PM'd you for address.
 

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I finally figured out that I was reefing way too hard on the crown wheel to get my measurement. It takes a very light touch.
I consistently got .05", or about .127 mm. Figuring in the .05 to .1 preload, my shim would likely require a .2 mm shim.
I measured my shim at .019", or .48mm - but likely a .5.
Assuming all this to be correct, I was overshimmed by .3 mm.

I was not able to get my bearing pulled, so I'll probably have the dealer do it when I go to get my parts. I'll get the new bearing seated, then measure, and order what ever shim I need.

Many thanks to Curtis through all this.
 

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fpmlt said:
I finally figured out that I was reefing way too hard on the crown wheel to get my measurement. It takes a very light touch.
I consistently got .05", or about .127 mm. Figuring in the .05 to .1 preload, my shim would likely require a .2 mm shim.
I measured my shim at .019", or .48mm - but likely a .5.
Assuming all this to be correct, I was overshimmed by .3 mm.

I was not able to get my bearing pulled, so I'll probably have the dealer do it when I go to get my parts. I'll get the new bearing seated, then measure, and order what ever shim I need.

Many thanks to Curtis through all this.
Yes, with the cover nice and warm with some drives it takes a very light touch. As a matter of fact in some cases with the cover warm the movement of the crownwheel assembly up and down can be done without the levers, just using fingers. Then as the cover cools, the resistance to movement increases and the levers become necessary. At that point, it may become more difficult to push the assembly back down fully. If the assembly doesn't fully seat, or come all the way up, obviously the observed gap will be measured as less than it acutally is. This is why it is important to make repeated measurements as the cover cools.

Local machine shop, automotive type, would probably pull bearing quicker and with less fuss than your BMW shop. That's were I'd go if I didn't have the tools.

Your measurement of a 0.05" gap is the smallest I've seen. Doesn't mean its wrong, but worth double checking. Not likely, but you are sure you don't have a second shim stuck in the bottom of the bearing seat in the cover? It would be a 0.15mm shim.

The shims rarely measure exactly at what the nominal thickness is. They are very often 0.02 or 0.03mm thicker or thinner than what the specification is. I have noticed this on new shims as well as old shims from failed drives. They make 'em like that; so much for German precision.
 

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Discussion Starter #10
CharlieVT said:
I just checked my inventory.... I've got 3 0.60mm shims. You can have one. PM'd you for address.
Thank you for the offer, but I'm running up to Max BMW Tuesday morning for parts. I'm only 15 miles away and I'm planning on having this back together by the afternoon. :)
 

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Curtis, I don't think there's any more shims in there, I cleaned it REAL well before sticking it in my wife's oven - self preservation. My son-in-law and I were going overboard with the measuring, he really enjoys learing, so gets into it big time. My bearing moved so freely that at one point, each of us would close our eyes and use only feel, while the other observed the dial. Consistently .05, probably 20 or more times. So we either read it right, or did it wrong a lot!!! It'll be interesting to see what the new bearing reads.
Should we be replacing the pilot bearing during all of this too?
 

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fpmlt said:
Curtis, I don't think there's any more shims in there, I cleaned it REAL well before sticking it in my wife's oven - self preservation. My son-in-law and I were going overboard with the measuring, he really enjoys learing, so gets into it big time. My bearing moved so freely that at one point, each of us would close our eyes and use only feel, while the other observed the dial. Consistently .05, probably 20 or more times. So we either read it right, or did it wrong a lot!!! It'll be interesting to see what the new bearing reads.
Should we be replacing the pilot bearing during all of this too?
Sounds good. I didn't think it was likely that you left a shim in there. Just thought I'd check with you on it. When all the shims are out you can see an oil channel at the base of the bearing seat.

Pivot bearings: very often are "notchy". Put a finger in the race and press in while turning the race, you may feel the "notchy-ness". If so, I'd replace 'em.
 

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I really wish there was a better way to measure as-assembled preload. Might it be possible to measure breakout torque (in the gear lash only) before the seal is installed? It would require an agreed-upon lube and would only work for new bearings (I think).

I hope your new bearing is the same as the old - but I wouldn't count on it.

Maybe a final shim from aluminum foil could be epoxied or Loctite'd to the case? The increment would be only about .0006 inches on the cheap foil I checked.

The range of shims available suggests pretty unnecessarily average manufacturing tolerances, which are so much easier to control now than they were say 25 years ago.
 

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Discussion Starter #14
Well, my first FD rebuild is behind me. I just got back from a test ride and it's now smooth and QUIET again. I left Max BMW at 9:20, got home with the parts at 9:45 and was riding at 11:30.

I measured the thickness of the old and new bearings with a micrometer and they both read the same down to 0.0001" (1/10,000) or 0.003mm. I measured at several points on the bearings.
 

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rcoolbaugh said:
Well, my first FD rebuild is behind me. I just got back from a test ride and it's now smooth and QUIET again. I left Max BMW at 9:20, got home with the parts at 9:45 and was riding at 11:30.

I measured the thickness of the old and new bearings with a micrometer and they both read the same down to 0.0001" (1/10,000) or 0.003mm. I measured at several points on the bearings.
Unhhhh...... you can't just measure the thickness of the bearing. There is axial movement between the inner and outer races that is measured when the bearing is mounted in place and measured using either DMAN's dial indicator method, or the BMW Service Manual depth micrometer method. So, I have to wonder, did you mount the bearing on the crownwheel assembly and go through the measurement process using the dial indicator, or just measure the bearing outer race thickness, find it to be the same as the old bearing and assemble it?
 

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I'm ready to do mine now. I have a very precisely cut screw driver - the tape is right on. I'll shove that into the gap between the bearing and the housing, mark it, then get a shim that meets that specific and precise gap. Should be PERFECT!!! ;) ;) ;) ;)(Hint Curtis, those are winks - check your leg for stretch marks)

Actually, I am on my way to get parts. Didn't you once mention that you liked the 19 ball unit better than the 17? NO WINKING, serious question.
 

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CharlieVT said:
Unhhhh...... you can't just measure the thickness of the bearing. There is axial movement between the inner and outer races that is measured when the bearing is mounted in place and measured using either DMAN's dial indicator method, or the BMW Service Manual depth micrometer method. So, I have to wonder, did you mount the bearing on the crownwheel assembly and go through the measurement process using the dial indicator, or just measure the bearing outer race thickness, find it to be the same as the old bearing and assemble it?
In the first post of this thread,he used the dial indicator method to verify the shim needed for the old bearing. If the new one is the same thickness,wouldn't the shim thickness be the same?

dan
 

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Discussion Starter #18 (Edited)
Right .... I did the measurement before I removed the original bearing and calculated the correct shim thickness. I wanted to verify that the new bearing was the same thickness which would make my calculation still valid.

I did measure both inner and outer races on both bearings. The bearings seem to be very consistent.
 

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But did you measure the internal axial clearance of the bearing? That would be the axial distance between the inner race on one side, and the outer racer on the other side. That is how the bearing's operating clearances or preloads are determined.

The race widths by themselves will be very accurate. It is the internal axial clearances that will vary - especially if the inner race is pressed or shrunk onto a shaft..
 

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fpmlt said:
I'm ready to do mine now. I have a very precisely cut screw driver - the tape is right on. I'll shove that into the gap between the bearing and the housing, mark it, then get a shim that meets that specific and precise gap. Should be PERFECT!!! ;) ;) ;) ;)(Hint Curtis, those are winks - check your leg for stretch marks)

Actually, I am on my way to get parts. Didn't you once mention that you liked the 19 ball unit better than the 17? NO WINKING, serious question.
No preference with respect to bearings. I've been using the German FAG 19 ball bearing in all my recent rebuilds. I am running the French 17 ball in my bike; for about 40Kmiles now.

Recently I tried a difference source and had a BMW dealership tell me there was a "new" bearing and they offered me the 17ball bearing for $130. I went back to my usual source of MaxBMW and got a German 19 ball for about $80.
Addendum: PLUS- I got the M&Ms!
 
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