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Thread: Which O Ring? '88 RT Rear Brake Cam Lube

  1. #1
    Registered User 88bmwjeff's Avatar
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    Which O Ring? '88 RT Rear Brake Cam Lube

    I was talking with someone who helped me with my winter project, and he suggested I take out the brake cam to clean and re-lube, which sounds like a good idea. Looking at the BMW parts fiche, there are two different O Rings indicated for O ring for the cam shaft (both are listed as part #20. FYI, this is not the felt ring, that's listed separately). One O ring is 10x2, while the other O ring is 12 x 1. Is there a way to determine which O rings I need prior to disassembly? The bike 1988 R100 RT.
    Jeff
    1988 R100 RT (the other woman)
    2018 R1200 GS (the mistress)
    "I got my motorcycle jacket but I'm walking all the time." Joe Strummer

  2. #2
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    BMW changed the rear brake cam pre 8/89 or post 8/89. I think the post 8/89 is the 12 x 1 as it lists the Mystic. for that part as well.
    Dave Hutton '78 R100S (mfg 7/77), '06 Kawasaki Concours, '82 Suzuki GS1100G, '82 Yamaha Exciter 250, '73 TS125

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    Registered User GTRider's Avatar
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    Check the production date on your bike. The 12 x 1 was started 1/26/87.
    Best,
    DeVern
    DGerber
    1983 R80ST 1984 R80 G/S-PD 2010 K1300GT 2018 R1200GS
    BMWMOA#52184, AMA#271542, IBA#138

  4. #4
    Fortis Fortuna Adiuvat Omega Man's Avatar
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    I would order both O-Rings. Just in case.
    OM
    "You can do good or you can do well. Sooner or later they make you choose". MI5
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    2009 F800GS 1994 TW200

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    Liaison 20774's Avatar
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    Adding to title for more clarity in future searches.
    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!

  6. #6
    Registered User 88bmwjeff's Avatar
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    Quote Originally Posted by Omega Man View Post
    I would order both O-Rings. Just in case.
    OM
    I don't mind spending a bucks or so, but, BMW charges about $5 each for the 12x1. The 10x2 is $0.50 each. I have no idea why the 12x1 is 5 times the cost of the 10x2. Granted, EME has them for $2.50 each, which is better, but still a bit much for my taste. I may change my mind though.
    Jeff
    1988 R100 RT (the other woman)
    2018 R1200 GS (the mistress)
    "I got my motorcycle jacket but I'm walking all the time." Joe Strummer

  7. #7
    Registered User 88bmwjeff's Avatar
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    Quote Originally Posted by GTRider View Post
    Check the production date on your bike. The 12 x 1 was started 1/26/87.
    Best,
    DeVern
    Bike was built in December 1987.
    Jeff
    1988 R100 RT (the other woman)
    2018 R1200 GS (the mistress)
    "I got my motorcycle jacket but I'm walking all the time." Joe Strummer

  8. #8
    Fortis Fortuna Adiuvat Omega Man's Avatar
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    Quote Originally Posted by 88bmwjeff View Post
    I don't mind spending a bucks or so, but, BMW charges about $5 each for the 12x1. The 10x2 is $0.50 each. I have no idea why the 12x1 is 5 times the cost of the 10x2. Granted, EME has them for $2.50 each, which is better, but still a bit much for my taste. I may change my mind though.
    Ordering the wrong size takes up time and, in this case, probably cheaper than the replacement shipping cost.
    This is how I deal with O-Ring woes-

    IMG_0812.jpg

    Both round and square edge style.

    OM
    "You can do good or you can do well. Sooner or later they make you choose". MI5
    Moderator Team.
    2009 F800GS 1994 TW200

  9. #9
    Registered User GTRider's Avatar
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    Quote Originally Posted by 88bmwjeff View Post
    I don't mind spending a bucks or so, but, BMW charges about $5 each for the 12x1. The 10x2 is $0.50 each. I have no idea why the 12x1 is 5 times the cost of the 10x2. Granted, EME has them for $2.50 each, which is better, but still a bit much for my taste. I may change my mind though.
    I get a lot of my o-rings from McMaster-Carr or my local hydraulics service and supply shop, for two reasons. First is cost, obviously, tho the difference between the two isn’t much on a $0.50 o-ring. For me, the bigger reason is I can select the material composition or durometer hardness I want. For example, the o-rings BMW used in brick-K clutches were buna-n as shipped, and they all tended to last around 65k miles before turning hard enough from heat to crack and start oiling the clutch disk. Replacing that o-ring with a Viton ring, with higher heat tolerance, resolves the issue. Same thing for the o-rings on the cam end covers on 90s oilheads.

    It would be a cold day in a hot place before I’d pay $5 apiece for those o-rings, but that’s just me. And, my advice is worth exactly what you paid for it.

    https://www.mcmaster.com/products/o-...000mm/id~12mm/


    https://www.mcmaster.com/products/o-...000mm/id~12mm/

    Best,
    DeVern
    Last edited by GTRider; 05-23-2023 at 08:36 PM. Reason: Links
    DGerber
    1983 R80ST 1984 R80 G/S-PD 2010 K1300GT 2018 R1200GS
    BMWMOA#52184, AMA#271542, IBA#138

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