Airhead main seal again.

Discussion in 'Airheads' started by pommie john, Nov 24, 2009.

  1. pommie john

    pommie john Long timer

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    This is a main seal question with a difference.

    It was fine for about 15 years ( I've owned the bike since the mid 90s) then last year the main seal started leaking.
    I had it replaced by an independent BMW shop who are normally very good, but after a year and two race meetings ( did I mention it's a race bike?) it's leaking again.

    I decided to do it myself this time and when I got the old seal out look what I found

    [​IMG]

    It seems that they've done a fair bit of damage removing the old seal and it's clear to me why the new one is leaking already/ You can see traces of loctite around the outside and that tells me that they've tried to stop it leaking. Why else would you fit a seal with loctite?

    Anyway. How can I fix it? Loctite clearly doesn't work, maybe silicone sealant or would metal paste like devcon or JB weld?

    Advice much appreciated.

    John
    #1
  2. krehmkej

    krehmkej Been here awhile

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    Man that sucks. After you burn their shop down..

    I'd surely try JB Weld. Clean really well with acetone before. Its really not stressed there, so would have a good chance of success.
    #2
  3. Infracaninophile

    Infracaninophile Finding My Way..

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    Pommie:

    Can you help ME understand what is wrong in the picture? I'm so new I can't even tell what's so obvious.

    Thanks,

    Tom
    #3
  4. pommie john

    pommie john Long timer

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    Sure. The seal sits in that machined recess. See that scrape across the recess ? Oil can get along that scrape, if you like it's going around the back of the seal and getting into the clutch housing.
    It was probably caused by the careless use of a big screwdriver to lever out a seal.
    [​IMG]
    #4
  5. bmwrench

    bmwrench Long timer

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    I'd use a silicone sealant to fill the scar before I installed the seal, then push a litle more in after it's installed.
    #5
  6. pommie john

    pommie john Long timer

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    Better than Devcon or JB weld? It feels quite deep.
    Loctite didn't seal it.
    #6
  7. jackd

    jackd Long timer

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    No big deal. I would use something like Yamabond or something of that nature to put around the outer circumference of the seal before I pushed it in. This is a non-rotational surface - the seal just sits there and so the blemish is not a big issue. It's the inner seal lip and what it rides on that's important.
    #7
  8. mcma111

    mcma111 Long timer

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    +1 on the Yamabond. jackd beat me to the punch with this one. You'd want to use a non-hardening type of sealer there. Don't know why there was loctite in there as it's not a thread. Might try polishing the gouge down some with 600 wet or dry sand paper. Push the seal in a little deeper. Good Luck
    #8
  9. Bloodweiser

    Bloodweiser honestly

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    Great timing.

    Just spotted this little dinger on my rear main

    [​IMG]


    it can just barely catch a finger nail... do I need to worry about it?
    #9
  10. batoutoflahonda

    batoutoflahonda Long timer

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    On airplane stuff, when we need to fill gaps, holes, scrapes etc. with thicker epoxy and sealants, we fill in the gap then go over the top with some 1 mil Mylar tape and let the goo dry. Then pull the tape. The result is a nice smooth surface that cuts way down on the sanding and forms better than just trying to work it in. Mylar works well because it's stiff, if you can get your hands on some. Thick packing or maybe scotch tape would probably work as well too.

    http://www.tapecase.com/p.2561.656/1-mil-clear-mylar-silicone-splicing-tape.aspx
    #10
  11. Steptoe

    Steptoe steptoe

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    Just thought i'd mention ( ignore me if you know) better safe than sorry, you do know that the center boss that's still on the end of the crank has to come off before you install the new seal.

    Remove center boss, install new seal, re-insert center boss.

    And you do know that you the front of the crank needs any play to be secured before re-installing the seal, boss and flywheel by wedging something between the front cover and alternator.

    If you move the crank forward slightly the inner crank thrust washers will drop off their mounting lugs and lock the engine up. Which means the crank out to reposition them.
    #11
  12. pommie john

    pommie john Long timer

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    hi Steptoe, yeah, that's under control thanks.I put the boss back to the give me something to lever against to get the seal out.

    Are you the Steptoe who's in Peckham? I heard about you from this forum. I lived in E Dulwich for years until i came to brisbane in 1999. Strange that we never came across each other.
    I bought a fair chunk of my bike from Adrian Rivett in E Dulwich. Do you know him?
    #12
  13. Wirespokes

    Wirespokes Beemerholics Anonymous

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    That may, or may not, be your problem. If it was good for a year then I wouldn't suspect that gouge. Perhaps the same guy who removed the seal also replaced it, and perhaps nicked or damaged the sealing surface. But I don't understand how it could have stayed sealed for a year and then started leaking. Was there an indication of oil seeping past there when the seal was removed?

    A guy in the area here has a 78S that he pushes pretty hard. At 100K it was weeping and replaced the rear main. It kept leaking, so figuring it hadn't been done properly, replaced it a second time. When it continued to leak, he started it up with out the trans in place, cleaned up, and talcum powder sprinkled all around in an attempt to see where the leak was coming from.

    Turned out the block had several cracks radiating outward from the rear main area and the oil was seeping from them.
    #13
  14. pommie john

    pommie john Long timer

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    I'll certainly look at that possibility.

    The thing is, it does really really low mileage. If it's not leaking a great deal it could take a couple of race meetings before the weep gets down to the step under the gearbox ? Maybe?

    From memory, I had the seal replaced, and did the big ends and rings etc at the same time.
    I then ran the bike in at one test session, say an hour and a half track time.
    Then I did one race meeting: two qualifying sessions of 15 minutes each, and three races, same again , so total 2 and 3/4 hours runnning so far.
    Add two hours on the dyno where I saw a slight weep on the shelf, and then the last race meeting where it leaked in qualifying, so I stopped.


    Total running time since the seal was changed: 5 hours
    #14
  15. RecycledRS

    RecycledRS Along for the ride

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    What are you doing to try and reduce the crankcase pressure? It could be that with the revs your turning racing the case pressure is biuilding too high and dumping out the rear seal.
    #15
  16. pommie john

    pommie john Long timer

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    Nothing much has changed over the years, so I can't really see that being the problem. At the last race meeting it was a very low speed circuit and I never got to full rpm, and it leaked there.

    I have a deep sump and longer oil pick up. This means I run the normal amount of oil, but it sits lower from the engine increasing the crankcase volume by a litre or so, and I have the later reed valve breather.

    I have just put a full fairing on it so it's getting a bit hotter. Maybe that could be an issue?
    The oil temp was 114C which isn't too bad.
    #16
  17. jackd

    jackd Long timer

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    This thread is ringing home to me. I will soon be into my third rear seal change in as many years. I actually suspect that this is the fourth seal in the bikes life. My attempt at re-surfacing the crank shaft guide ring is what I suspect as being the cause of my latest leak. The plan is to buy a new guide ring. When I pulled the clutch housing last time, there was no clear indication of what was the cause except for some dampness around the inner seal lip area. The pump cover o-ring, as well as the guide ring o-ring were also replaced. The knowledge that others have also had multiple seal changes gives me hope that the guide ring might be the cause. But I might start looking for cracks in the housing (Bike has only 46k on it) Running it withough the transmission might be a thought as well. Anyone else ever tried re-surfacing their guide ring and had bad results?
    #17
  18. Wirespokes

    Wirespokes Beemerholics Anonymous

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    There are other things that can cause leaks back there. One of them is the ORing at the guide ring. It fits between the crank and guide ring. I don't know why that one is so important, but it is. I chased a leak several times before finally replacing that sucker just because I'd done everything else, and it went away.

    If your crank bearings are worn it can cause excessive rocking at the crank/seal connection and allow a leak.

    I also remember when the new style seals first came out, some guys had problems getting them to work, and there were all sorts of different ways to prep and install them.
    #18
  19. jackd

    jackd Long timer

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    So what are these ways of prepping these new seals? I put mine in dry as has been the suggestion in this forum. Others do different. I install many seals in my trade and I have never seen a fussier set-up than this. Rank novices are having better luck than an old salt like me!
    #19
  20. Wirespokes

    Wirespokes Beemerholics Anonymous

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    I don't recall the variations I'd heard back then. I think the accepted method now is to soak them in oil for several hours stretched over a comparable surface like the guide ring. Check 'the bum' for his take on it.

    As I recall, the guide ring is highly polished. How did you re-surface it? It just may be it needs replaced, and those dumb things aren't cheap (as if anything on these bikes is!).
    #20