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Thread: Output shaft noise

  1. #1
    Don't forget your towel
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    Output shaft noise

    Over the past several months my '91 K100RS with 60,000 miles on it has developed an increasingly loud knocking noise at idle. Louder than the usual clutch rattle, this also doesn't go away when I pull in the clutch lever... We also have an engine oil leak coming from the tranny to engine joint and out the weep hole. Paging through Clymer they mention a Service Bulletin from 1988 that had something to do with bad springs in the output shaft. Can somebody enlighten me? I clearly need the put a new main seal in so dropping the oil pan to work on the shaft appears to be just a few more bolts away. I had been planning to get a lift this winter anyway I guess this just moves it up on the priority list.

    Steve

  2. #2
    looking for a coal mine knary's Avatar
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    Rear main seals on old K-bikes eventually leak. If you've only got a slow weep, I wouldn't worry about it. And rather than being the seal, it's very likely that it's the large O-ring on the output shaft. If your bike is due for a clutch spline lube, you might consider going ahead with the additional work.

    As for the knocking sound, it might be something as simple as the alternator rubber bushings. If this is the problem, the knock it produces can be pretty unsettling - and, of course, has nothing to do with the clutch/tranny.

  3. #3
    Blocking the slow lane
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    Unfortunately Steve, progressing from the main seal area into removing the output shaft is pretty significant work. The rear bellhousing and water/oil pump need to come off before the bottom sump (which holds the output shaft) can be removed. I also don't know if the frame has to be lifted up for this kind of access.....how badly is this noise bothering you?
    Jon Diaz
    BMW K75/K12GT
    BMWMOA Ambassador

  4. #4
    Don't forget your towel
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    You're right, getting to the shaft IS a lot of work, I'm hoping I don't have to go through the process. The question I hope to have answered here is what did the Service Bulletin mentioned in Clymer refer to? I have an oil leak and it's time for a spline lube so I'll have to pull the bike apart anyway. With a bit of luck only the alternator bushings are shot....I can already sense this project getting out of hand as I contemplate all those 12 year old rubber bits so nicely "out of sight, out of mind" while covered by bodywork. At least it'll be up on which ever lift I decide to get. (Waffling between a "Lift-Buddy" (lift-buddy.com) and the "pro-cycle" from Direct-Lift (directlift.com) leaning towards the lift-buddy but that is a subject for a different thread)

    Can I live with the noise if it turns out not to be the alternator bushings? Well, that depends on whether or not a problem with the output shaft's internals is simply going to tear up another oil seal, the old adage "in for a penny, in for a pound" strikes again while maintaining a BMW. Once you get the back end of the bike torn apart and supported to get the clutch removed, dropping the motor out doesn't seem like all that much more work.

    Anybody want to chime in on best methods for pulling the output shaft oil seal without dropping the oil pan? Sheet metal screws and a prybar? Is the "clutch centering tool" for the Ks the same one I have for my airheads? (Probably too much to hope for...)

  5. #5
    bmwmick
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    Steve,
    I've had my Lift-Buddy for a little over a year and I love it! You can't go wrong with this choice.
    The leak you have is probably the O-Ring, like Scott said. I did mine last year (just before buying my lift)
    My rear oil seal was like new at 120,000 miles. I replaced it anyway, along with the tranny input shaft seal even though it wasn't leaking. While I was there, I replaced the alternator drive rubbers, mine were OK but it's an easy job once the back of the bike is disassembled.

    Mick

  6. #6
    Blocking the slow lane
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    Originally posted by sgborgstrom
    Anybody want to chime in on best methods for pulling the output shaft oil seal without dropping the oil pan? Sheet metal screws and a prybar? Is the "clutch centering tool" for the Ks the same one I have for my airheads? (Probably too much to hope for...)
    Steve, we used an automotive main seal removal tool to get out the old one, and it was a bargain at ~$7. It cantilevered the old one right out, and will also double as a fork seal removal tool when the time comes for you to do that.

    I got my K clutch tools from Ken Lively, but I'm sure the airhead one will work fine.
    Jon Diaz
    BMW K75/K12GT
    BMWMOA Ambassador

  7. #7
    ziegelreiter
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    Quote Originally Posted by sgborgstrom View Post
    Over the past several months my '91 K100RS with 60,000 miles on it has developed an increasingly loud knocking noise at idle. Louder than the usual clutch rattle, this also doesn't go away when I pull in the clutch lever... We also have an engine oil leak coming from the tranny to engine joint and out the weep hole. Paging through Clymer they mention a Service Bulletin from 1988 that had something to do with bad springs in the output shaft. Can somebody enlighten me? I clearly need the put a new main seal in so dropping the oil pan to work on the shaft appears to be just a few more bolts away. I had been planning to get a lift this winter anyway I guess this just moves it up on the priority list.

    Steve
    I may be hearing this same noise from the output shaft springs.
    My question is about the BMW Service Information Bulletin mentioned above.
    Is a Service Information Bulletin just something to give the mechanic at the dealer a heads up on what may be causing the problem or is it like a recall that's covered by BMW?

  8. #8
    Registered User
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    The noise may be the output shaft rivets or the thin gear that has a spring on it to keep the crank gear and output shaft from having any free play. google k100 output shaft rivets there is quite a lot of info out there, you should have the uprated 12 rivet shaft but you can look by opening up the crank cover and watching the output gear while moving the rear wheel back and forth with bike in gear, there should be no free play. I just did the job 87 k100 rt, not to bad really.

    Brian
    Brian

    86 k100rt, 78 r80/7

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