BMW Rear Main Seal Nightmare

Discussion in 'Airheads' started by bmwhacker, Jan 12, 2012.

  1. bmwhacker

    bmwhacker Still on 3 wheels

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    I just completed (so I thought) a rear main seal replacement / oil pump seal replacement on my R100S engine.
    The new seal began leaking within a 100 miles. Pulled the flywheel back off yesterday and carefully cleaned / dressed the mating surface on the flywheel. The surface had a little discoloration prior to cleaning it up with crocus cloth. The flywheel surface looks good, no wear or grooves visible to the eye.
    Put it back together this AM and again am beginning to lose oil from behind the transmission. :baldy
    The old original seal was loose in the bore and I was able to pull it out with my fingers.
    The new seal went in nice and snug. ....I have an aluminum disc that fit the seal outside diameter and was able to "tap" the new seal in without any trouble. The seal looked straight and was not messed up on installation.
    One thing I noticed, the seal lip on the "new" seal is a very hard material and not soft like most seals I've seen.
    Is that normal?....or did I get a 40 year old "new" seal?
    I'm running out of ideas on what in the world is wrong...or what I'm doing wrong....:deal
    Any inmate insight and opinions would be appreciated.

    I just ordered another new seal and I'll be able to remove the transmission blindfolded with all this practice.
    Bike is hooked to a sidecar so that makes it even more fun to remove.:cry
    #1
  2. Wirespokes

    Wirespokes Beemerholics Anonymous

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    There's another hidden o-ring that could be causing this. And I don't know why it is - makes no sense to me, but it's on the guide ring - that piece on the end of the crankshaft the flywheel bolts to. Part # 11221337099.

    I've gone through similar with an R65.

    If it's not that, then it's time to check for cracks in the block.
    #2
  3. bmwhacker

    bmwhacker Still on 3 wheels

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    Ya, I did replace that o-ring too. Found a little "crud" in the groove but cleaned it well before installing the new o-ring.
    I'll also remove the new oil pump o-ring and inspect it to be sure I didn't mess it up. I ordered another pump cover o-ring too.
    I'm still questioning the "brittleness" of the "new" main seal material. I've never handled one before but the rubber was really hard and stiff....
    #3
  4. Wirespokes

    Wirespokes Beemerholics Anonymous

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    The new seals are teflon - kind of a brownish material. And they're flat when you get them, no spring like the old ones.

    I remember ten years ago guys having difficulty with these things - and there were three or four different ideas how to install them - some even contradictory. I've installed a couple with good luck and they haven't leaked, but always kept my fingers crossed.
    #4
  5. supershaft

    supershaft because I can

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    Those seals have been out now for 30 years? 25 for sure. They are ten times better than the rubber ones. Install them just like a normal seal.

    Pump O-ring? Somebody was sealing the wrong part recently. It wasn't BMW.

    The O-ring is on the guide plate to keep oil from leaking out the flywheel bolts. Later flywheels have the same thing for the same reason. It works.
    #5
  6. pommie john

    pommie john Long timer

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    #6
  7. bmwhacker

    bmwhacker Still on 3 wheels

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    I'll look the block over real good when I go in for the 3rd. time.
    The 1977 engine rear main seal seats directly on the flywheel. I see in the thread above photos that the configuration is different.
    Is there any way oil could come through the flywheel mounting bolt threads?
    The flywheel internal o-ring wouldn't stop oil from getting through the threads. I did replace the flywheel bolts.
    #7
  8. bgoodsoil

    bgoodsoil Dare to be Stupid

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    Did you make sure to put the seal in and then the guide ring? The teflon 'ribs' won't ride on the guide ring if you put in the guide ring first. If the guide ring is already on the crank when you install the seal then the ribs will get pushed out when you press it in.
    #8
  9. bmwhacker

    bmwhacker Still on 3 wheels

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    Nothing resembling a "guide ring" under the flywheel. The flywheel bolts directly to the crank end. It appears that the flywheel end sits directly on a thrust bearing surface.


    mine doesn't look like this....this must be a later model.

    [​IMG]





    Mine looks more like this:
    (Stole this from "pbeckm's" /6 thread)

    [​IMG]

    Photo from the first flywheel removal / cleanup.....I was surprised to find a drilled flywheel living there. It doesn't weigh much.

    [​IMG]
    #9
  10. supershaft

    supershaft because I can

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    The flywheel O-ring doesn't keep oil from going through the bolt holes. It keeps the oil from getting to the bolt holes.
    #10
  11. bmwhacker

    bmwhacker Still on 3 wheels

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    Gotcha.....The flywheel bolt holes in the crank must be "dead end" holes.(?)
    #11
  12. bmwrench

    bmwrench Long timer

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    Yes, they are blind holes. Occasionally oil will get past the o-ring and trickle past the bolts in a very small quantity. It is obvious when this has happened-a bit of oil will be found on the inside of the wheel, and some will run out when a bolt is removed. If this is the case, put a light ring of sealant (I use Hylomar) under the bolt heads where they engage the bolt hole only. It is most likely that your seal preparation and installation weren't correct; the teflon lip must be gently shaped to accept the flywheel. You can do that with a clean fingertip. Use a small amount of WD-40 to ease the seal into the case. The outer face of the seal should be just inside of the bevel in the seal bore. Do not lube the seal surface where it contacts the flywheel with grease; it is intended to be run in dry. Grease won't hurt the seal material, but can prevent it from "seating".

    Don't lose heart. I think all of us were stunned when this seal was introduced. I remember calling BMWNA and telling them they'd got a batch of unfinished seals. History has proven this seal to be an excellent design.

    This seal was introduced about 1988, so SS is on the mark. It pleases me that BMW continued to refine these bikes so late in the series run.
    #12
  13. bmwhacker

    bmwhacker Still on 3 wheels

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    On the 2nd. go-round I did use a small amount of "BMW #10" lube on the seal..... Oops...Used no lube the first time around. .Thinking about running it a while as is and see if the leakage subsides...wishful thinking.... I only drove it about 10 miles and see a small bit of oil coming from the "shelf". I'll run it a few more miles and see what happens. Just don't want to oil "foul" the new clutch plate.
    If the leak persists I'll replace the two o-rings and the seal again and maybe go back to a stock flywheel.
    #13
  14. supershaft

    supershaft because I can

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    My nitty gritty advise is slightly different. I never preshape the seal with my fingers. I don't touch it per BMW's slightly later advise. The seal boss in the case often needs chamfered with a Exato razor blade or the sharp edge will peel the ribs on the seal's OD. I lube the OD with a bit of motor oil. Knock on wood I have never had a problem that I know of.

    What about your pump cover O-ring? There are some wrong parts for that out there.

    Don't worry about reusing the 11mm bolts per BMW but I always replace the 10mm bolts!
    #14
  15. wirewrkr

    wirewrkr the thread-killer

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    make sure it's actually motor oil on the shelf. Trans oil smells totally different.
    Also, sometimes the oil pump cover is actually loose!
    I have seen that more than once.
    #15
  16. bmwhacker

    bmwhacker Still on 3 wheels

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    I bought a complete engine gasket set from Huckys so they appear to be BMW OEM stuff.
    I did replace the oil pump seal while I was in there. I'll revisit that again next time in. When I pulled the flywheel this time, oil was all over the rear so I can't tell exactly where it is coming from.
    I'll definitely look for anything resembling cracks.
    Oddly the original rear seal I removed was loose in the bore.... I picked it out with my fingers.
    #16
  17. Boxer Metal

    Boxer Metal Mad Scientist

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    x2. I was thinking the same thing as I was reading this thread. If the oil smells like cat but then it's gear oil. It looks like you got the seal in straight so in theory the seal should be fine. I have never had the newer style seals leak.
    #17
  18. bmwhacker

    bmwhacker Still on 3 wheels

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    Motor oil / Gear oil is like comparing Coors Light to Guinness Stout:freaky (I prefer the Guinness)
    I've been absorbing automotive related fluids (some toxic?) since I was 12.:lol3
    #18
  19. supershaft

    supershaft because I can

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    Those oil pump cover threads in the case are prone to mess up. I suspect that between people over tightening them and then using all kinds of different goop including red Loctite they have a hard life. I also suspect they get taken off a lot for no reason because it is usually the RMS leaking and not the oil pump but that is another story. I heat those bolts up hot every time before I break them loose in case they have red Loctite on them. The threads often need cleaning. I use a role tap or thread chaser and not a regular tap. Those are precious threads and cleaning threads with a cutting tap removes quite a bit of precious material. I highly recommend having a couple of role tapes around. They are great for saving threads as well as rolling them. All your serious threads are rolled these days anyway. You can tell by looking at them with a magnifying glass.
    #19
  20. Wirespokes

    Wirespokes Beemerholics Anonymous

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    Since your flywheel is swiss cheesed, I'd suggest running the engine while the transmission is off, and observe where/if it's leaking. Clean the block really well and sprinkle talc/baby powder on the rear of the block to make the leak really stand out.

    Your engine has a guide ring, it just looks like the end of the crank you're looking at. Take a look at the flywheel bolt holes - they not threaded to the surface - the unthreaded part is the guide ring.

    Removing them can be a bitch, especially evidenced by the damage they suffer at previous hands. But we don't need the damage to prove that to us. :lol3
    #20