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Thread: Major engine oil or 80/90 leak - R100GS

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  1. #1
    Registered User ohiorider's Avatar
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    Major engine oil or 80/90 leak - R100GS

    Approx 500 miles after a Master BMW mechanic with years of airhead experience. All previous work he has performed on this bike have been without issues. (between 60,000 and 155,000 miles)

    - replaced the clutch plate.
    - rear main seal.
    - pulled tranny - replaced major bearings and wear items in shift mechanism.
    - other odds and ends that are not related to this problem.
    After 400 + trouble free miles, I took the old gal out for 70 miles on a semi-pleasant January Saturday.
    Returned home, parked the bike in the garage, warmed up with hot shower. Called it a day.

    The following day, I went to the garage to plug in the trickle charger, and found a very large (and getting larger) puddle of either engine oil or 80/90 gear lube on the floor. It appeared to be coming from around the rear swingarm boot, where it attaches between swingarm and final drive.

    The mechanic has asked me to return the bike to his shop, which I'll gladly do when we have a day over 40F, and no snow on the ground. In the meantime ........
    a couple of questions:
    - I can't tell from smell or feel whether the leak is engine oil or gear lube.
    - I'd like your opinions on possible sources of such a large leak.
    - Does the airhead have any breathers that could possibly clog up or fail, causing such a mess?
    - Could engine oil (if rear main failed) make its way into the swing arm?
    - Could tranny lube makes its way into the swingarm?
    - Could final drive lube?
    - Any possibility that the final drive seal(s) may have failed?

    Since the shop will dismantle and repair, my questions are purely academic

    Thanks in advance for any thoughts you can offer.

    Ohiorider

  2. #2
    Registered User PAS's Avatar
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    Check your private message.

  3. #3
    Liaison 20774's Avatar
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    Look around to see the highest point where things are wet...that will help to find the source of the leak.

    - engine oil can't get back to the driveshaft unless it runs along the bottom of the oil pan
    - the speedometer cable bolt has a hole down the center which is designed to allow the transmission to "breathe" as fluids heat/cool
    - I believe there is a notch at the 12 o'clock position in the seal at the output shaft of the transmission...nominally this is open...some models it is closed

    Given that the mechanic took the transmission out and apart (from what I can read) the problem must be associated with the transmission. Or it could be with the boot that connects at the back of the transmission. R100GS...I forget if these driveshafts take oil or not...I think so but the paralever models did not have any oil in the driveshaft. You can tell if the final drive seals have failed by seeing if the fluid level is low in the housing. If it's where it should be, then that's not the problem.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  4. #4
    Registered User b25bsaboy's Avatar
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    Quote Originally Posted by ohiorider View Post
    Approx 500 miles after a Master BMW mechanic with years of airhead experience. All previous work he has performed on this bike have been without issues. (between 60,000 and 155,000 miles)

    - replaced the clutch plate.
    - rear main seal.
    - pulled tranny - replaced major bearings and wear items in shift mechanism.
    - other odds and ends that are not related to this problem.
    After 400 + trouble free miles, I took the old gal out for 70 miles on a semi-pleasant January Saturday.
    Returned home, parked the bike in the garage, warmed up with hot shower. Called it a day.

    The following day, I went to the garage to plug in the trickle charger, and found a very large (and getting larger) puddle of either engine oil or 80/90 gear lube on the floor. It appeared to be coming from around the rear swingarm boot, where it attaches between swingarm and final drive.

    The mechanic has asked me to return the bike to his shop, which I'll gladly do when we have a day over 40F, and no snow on the ground. In the meantime ........
    a couple of questions:
    - I can't tell from smell or feel whether the leak is engine oil or gear lube.
    - I'd like your opinions on possible sources of such a large leak.
    - Does the airhead have any breathers that could possibly clog up or fail, causing such a mess?
    - Could engine oil (if rear main failed) make its way into the swing arm?
    - Could tranny lube makes its way into the swingarm?
    - Could final drive lube?
    - Any possibility that the final drive seal(s) may have failed?

    Since the shop will dismantle and repair, my questions are purely academic

    Thanks in advance for any thoughts you can offer.

    Ohiorider
    Good morning,

    I had a chuckle with the following comment, as this happened to me on when I rebuilt my first AirHead:

    The rubber boot that fits over the drive shaft that connects the swing arm and rear transmission flange has clamps both front and back. I forgot to snug them down, thus when riding the oil migrated up the shaft as its supposed too, settles in the lower pocket. If the clamps are not tight, it will weep.

    Tightened mine down, and not a drop there after. This is a common over looked mistake that we all at one time or another make!
    Rick MacPherson
    Success is Not a Destination, But a Journey.
    Accredited Motorcycle Appraiser
    1968 BSA Starfire, 73 R75/5 SWB, 2008 Honda GL-1800 Lehman Trike

  5. #5
    I don’t think that the paralever bikes had oil in the driveshafts. If there’s oil at the boot, it’s almost certainly out of the transmission, though I’d have to believe that hypoid oil would be discernible by aroma. If the output seal has failed, was the tranny overfilled, or was the vent bolt replaced with a conventional one?

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