R100 Rear Main Seal R&R

Discussion in 'Old's Cool' started by StumpThumper, May 4, 2009.

  1. StumpThumper

    StumpThumper Adventurer

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    I'm sure this has been covered a dozen times but this is my first rear main seal replacement. The bike is a '84 R100. I replaced the rear main seal following the steps in my Haynes manual. After putting it back together I get a chirping sound from the clutch area at idle after it gets good and warmed up. When it cools after stopping for a few minutes it no longer chirps until it get hot again. It stops when revving the engine but returns at idle. I called Bob's BMW and spoke to a tech there who said if I let the crank move forward the thrust washer can slip off it's pins and get wedged in between the flywheel and bearing. It would have been nice if the Haynes manual had mentioned this. I removed the clutch, the brand new rear main seal and right jug to look at the bearing. Both the front and rear thrust washers are still pinned but there doesn't seem to be much end play in the crank. Anybody got any ideas on what I need to check next? I was a Honda / Yamaha mechanic back in the 70's and have done lots of restorations but this is my first airhead. (I'm digging it!) Any help would be appreciated. I checked the airhead tech pages but my clutch and flywheel doesn't look like R90 in their pictures. Thanks in advance.
    #1
  2. bmwrench

    bmwrench Long timer

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    If the thrust washers had moved, you wouldn't have been able to rotate the crankshaft. End play is very small in these motors-from memory .004-.008", though it is frequently even tighter than .004". Did you use the latest seal, the teflon type with no garter spring? Is it placed where it should be? And did you oil the seal lip?
    #2
  3. AntonLargiader

    AntonLargiader Long timer

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    If the washer has slipped off and you reinstalled the flywheel, it will look like that but in fact the mounting pins may be punching new holes in the bearing. The end play is really small (probably less than 0.10mm wet) and I'm not sure how you can really tell without pulling the crank. Possibly the pins have been pushed back slightly toward the flywheel; that would be one sign.
    #3
  4. StumpThumper

    StumpThumper Adventurer

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    I did use the teflon seal; I didn't oil it first. If a dry seal is making that noise then I now know how crickets are so loud.
    With the flywheel removed and the right jug removed I can just see the pins in the thrust washers so I know they haven't moved. I read too late that I should have measured the depth of the original seal and seated the new one at the same. How do I determine the depth now? Could that be causing the chirp?
    #4
  5. jackd

    jackd Long timer

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    The instructions of whether or not to lubricate the seal lip always baffled me - some do and others (that would be me) don't. Does oiling this lip lead to oiling wicking past the seal? Someone please explain.

    My guess is that you might have got away with changing the seal without blocking the front of your crankshaft. You would have problems with turning the motor over now if the thrust washers have dropped out of their positions. They do instruct you to lubricate the contact areas of the diaphragm spring during re-assembly - did you do this? I would guess that your clutch actuation thrust bearing is giving you the cause of your noise. I would start looking at this area first.
    #5
  6. Country Doc

    Country Doc Wanderer

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    +1 on suggestions from Jackd. I had very similar symptoms and the problem was the clutch throwout bearing/piston. When I reinstalled it after replacing the tranny, the little seal lip had twisted/flipped over, because it's a pretty tight fit in there, and I didn't notice the first time.

    I took it out, cleaned it up, greased the throwout bearings, replaced the little seal, and carefully worked the piston back in with a small screwdriver to prevent the seal lip from flipping back, and that solved the chirping for me.

    Might not be your problem but it's a quick and easy check.

    dc
    #6
  7. bpeckm

    bpeckm Grin!

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    Thrust bearing, thrust rod etc are possibilities... presumably you have listened for noise with clutch engaged, disengaged, slowly engaging, etc. But as noted above, it is a very easy check to pull the rod and thrust bearing and check it all. I put a touch of moly on the end of the thrust rod as well.

    :D

    Another thought: does the chirping get faster and higher pitched as you slowly rev? With the '84 you probably have the ball bearing throwout, if it is a separate-able piece from the plastic carrier, the carriers have been known to "grow" when warm.... though they are not supposed to rotate, if the throwout bearing is bad it could be trying to rotate that part as well?
    #7
  8. StumpThumper

    StumpThumper Adventurer

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    When I heard the chirping the first time I figured it was a dry clutch plate as I cleaned all the clutch parts before reassembly. I removed the pressure plate and lubed it with moly. I just knew this was the problem. I also checked the throwout bearing and lubed it with Belray waterproof grease. I put a light coat of grease on the entire push rod. I didn't put moly on the top of it though. The chirping does follow engine rpm. It is a high pitched metallic sound like the flywheel is scrapping steel.
    I just noticed where the flywheel mates against the crank has several polished spots. Could it be the flywheel is dancing around on the end of the crank? It seems odd that it wouldn't be pinned where it couldn't move. There is certainly enough room in the bolt holes for movement. I torqued the bolts to spec but I didn't use new ones. Maybe they streched?
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  9. Country Doc

    Country Doc Wanderer

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    weird.

    FWIW, BMW does say to never reuse the flywheel bolts, as they do stretch, apparently, when torqued. Same with the driveshaft bolts, though that is apparently less critical, and many reuse them if they thread in smoothly.

    dc
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  10. StumpThumper

    StumpThumper Adventurer

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    I ordered a new seal, new flywheel bolts and new Ujoint bolts this morning. Hopefully this will fix the problem. Thanks for all the replies.
    #10
  11. bmwrench

    bmwrench Long timer

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    If the flywheel has been touching the seal, that's where the noise is coming from. Put the next one in just a bit farther. An old service bulletin suggested we install the flywheel and check for proper seal seating. Sounds like it might be the right thing to do, especially in your case.

    I would not reuse the flywheel bolts in any case. Have you seen what a new crankshaft costs? Makes bolts look very inexpensive.
    #11
  12. jackd

    jackd Long timer

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    Where would a person find these old Service Bulletins? There isn't much info in the factory manuals and the Clymer is also lacking in details. Anywhere on the net that you can go to get these?
    #12
  13. StumpThumper

    StumpThumper Adventurer

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    The flywheel was not touching the seal. My flywheel fits flat against the end of the crankshaft and no part extends past it. The seal had plenty of clearance past the end of the crank. Is it possible to push the seal in too far? It appears to have a shoulder that it seats on.
    #13
  14. PaulRS

    PaulRS Dutch fool

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    In my manual it says it is ok to reuse the old bolts, just torque them up to 130Nm.

    Don't know where this comes from, though, I never heard of a sb from Herr BMW regarding this :deal

    5 bolts for less then 10€, it's a no-brainer.

    Paul.
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  15. outfit

    outfit Been here awhile

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    I did my rear seal last year on a R100 - 1981, so it is the same engine.

    The seal was flush to the casing. I suspect if you put the seal in upto the shoulder then you have put it in too far.

    Maybe a silly question but, when you replaced the seal you will have taken the 'centre boss' out before the seal goes in? If you did'nt the seal lip will be facing the wrong way.

    Safe riding Karl.
    #15
  16. Joerg

    Joerg Long timer

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    Hi,
    May I ask where this information comes from, please? :deal

    The factory manual does not mention anywhere that new bolts should be used here, and these are certainly not stretch bolts - neither on the flywheel nor on the driveshaft. If these were stretch bolts, then the instructions would probably read something like "torque to 100 Nm, then add 1/4 turn". Which is not the case.

    The BMW factory manual says 100 Nm. What are you reading ... ? :deal

    Btw, full story of my recent crankshaft seal change here: http://jhau.maliwi.de/mot/r80gs.htm#cseal The replacement seal is supposed to be "pre-formed" and oiled before installation.

    [​IMG]
    #16
  17. PaulRS

    PaulRS Dutch fool

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    Reused bolts can, I say can end in this :cry

    [​IMG]

    One fokked-up crank and fly-wheel.

    Still feel lucky and saving 10€?? :evil

    Paul.
    #17
  18. AntonLargiader

    AntonLargiader Long timer

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    I can't be sure, but if those dimples in the seal are hammer marks from installation I would question the entire repair history of that part of the bike. I would think that if they are from the flywheel hitting it there would be other marks back there (such as on the oil pump cover), and there aren't.
    #18
  19. PaulRS

    PaulRS Dutch fool

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    Haynes.

    @Anton, the seal came loose with the flywheel, I just hammered it back in not to loose the shim behind in transport.

    Paul.
    #19
  20. StumpThumper

    StumpThumper Adventurer

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    I formed the lip around a piece of tubing that was close to the same size as the crank and then used a popsicle stick to guide the lip over the crank when I installed it. I wasn't sure if the centre boss was removable; I haven't been able to move it but haven't tried a puller either.
    #20