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Thread: restoring a 1976 BMW R75/6 - Oring Cross Over

  1. #31
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    Feb 2006
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    9

    Ever have any luck?

    Quote Originally Posted by b25bsaboy View Post
    Good afternoon,

    Finally after several years I am getting to the 76 BMW R75/6 restoration. Just pulled the backend where the flywheel is located and placed my order with my local BMW dealer when the thought crossed my mind, in that has anyone crossed over the BMW part number to a Parker O-Ring number? I just find it frustrating in that I want to complete the reassembly, only to have to wait till the parts arrive which sometimes takes up to ten (10) days.
    I realize this thread is somewhat old, but was just wondering whether you found the o rings you were looking for. I took my used o rings to a local place where they measured them and sold me a couple of viton rings for the oil pump cover and the flywheel. I'm still a little nervous about using them, but they look like they should work. If I use them, I can get everything back together today, which would be nice. Otherwise, it will probably be Monday before the ones I ordered arrive. The ones I got are -Flywheel 57mmx63mmx3mm. Oil pump cover- didn't have a metric, but gave me a 2-3/8 X 2.5 x 1/16.

  2. #32
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    Quote Originally Posted by Gary Lee View Post
    I realize this thread is somewhat old, but was just wondering whether you found the o rings you were looking for. I took my used o rings to a local place where they measured them and sold me a couple of viton rings for the oil pump cover and the flywheel. I'm still a little nervous about using them, but they look like they should work. If I use them, I can get everything back together today, which would be nice. Otherwise, it will probably be Monday before the ones I ordered arrive. The ones I got are -Flywheel 57mmx63mmx3mm. Oil pump cover- didn't have a metric, but gave me a 2-3/8 X 2.5 x 1/16.
    Do you mean oil pump cover, or do you mean oil filter cover?

    If you know the exact o-ring size (metrics are also available) you can substitute ones from an o-ring supplier like McMaster-Carr.

    Several things besides just size are also critical. The material - must be heat and oil resistant - vitons were used on hot plastic hydraulic machines, but there also is teflon, and other materials like buna - read MCarr page and it explains uses for various materials. Also critical is the durometer rating - this is how hard the oring is. 70 durometer is common, but at the plastics factory, they liked 90 better - less deformation under pressure.

    One other thing, when determining oring size, be careful as some of the methods are a little "iffi." Also, try to use the proper oring for the location and measure a NEW one. Some orings get distorted after use, and sometimes expand, and sometimes shrink or get hard and brittle which makes measuring more difficult.
    "The difference between death and taxes is that death doesn't change every time congress meets." - Will Rogers

  3. #33
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    Thanks Jimmylee. I guess I had better just be patient and wait for the parts to arrive.

  4. #34
    Registered User b25bsaboy's Avatar
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    Quote Originally Posted by jimmylee View Post
    Do you mean oil pump cover, or do you mean oil filter cover?

    If you know the exact o-ring size (metrics are also available) you can substitute ones from an o-ring supplier like McMaster-Carr.

    Several things besides just size are also critical. The material - must be heat and oil resistant - vitons were used on hot plastic hydraulic machines, but there also is teflon, and other materials like buna - read MCarr page and it explains uses for various materials. Also critical is the durometer rating - this is how hard the oring is. 70 durometer is common, but at the plastics factory, they liked 90 better - less deformation under pressure.

    One other thing, when determining oring size, be careful as some of the methods are a little "iffi." Also, try to use the proper oring for the location and measure a NEW one. Some orings get distorted after use, and sometimes expand, and sometimes shrink or get hard and brittle which makes measuring more difficult.
    Good morning,

    Thought I should jump in here and add some comments to JimmyLees. When I originally posted the question, I honestly thought O-rings are a standard size both in the Imperial Measurement and Metric. After spending some time at the local o-ring supply house here in Calgary, I came away being more confused than when I went in. I agree with the term "iffie", in that JimmyLee is on to something. Thought about it hard and long and decided to just wait and order the BMW OEM supplied material, cause I hate redoing things a second time because of either being in a rush or using something that I shouldn't have.

    Just to add to the Durometer information, in that the harder the material the less likely you will have absorption from outside medium or gases. I have seen this first hand in my world were Viton Durometer 70 O-rings were exposed to H2S (Hydrogen Sulphide) and the o-rings absorbed the media and expanded 10 times its original size. That is a no no when working around piping and transmission equipment especially when lives are at risk, as one whiff of H2S can knock you down and send you to the gates of heaven.

    Bottom line is, use BMW OEM supplied material, as you know your getting the right material and size.
    Rick MacPherson
    Success is Not a Destination, But a Journey.
    Accredited Motorcycle Appraiser
    1968 BSA Starfire, 1976 BMW R75/6, 2009 R1200RT

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