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Thread: What is this O Ring?

  1. #1
    Join Date
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    What is this O Ring?

    I was taking off some old gasket around the water pump, lower cover area and this O ring suddenly popped off from somewhere. Any ideas as to where I should look where it may have come off of?IMG_7533.JPGIMG_7534.JPGIMG_7535.JPG

  2. #2
    Join Date
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    2007 Z4 M Coupe
    This might help:

    IMG_7545 (1).JPG
    Current: 2007 Z4 M Coupe (blue/black)
    Previous: 2001 740iL Sport (black/black), 2000 528i Sport (black/tan), 1995 318is (black/black), 1991 318is (white/black)

  3. #3
    Join Date
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    98 740il, 00 540i,04 ZHP
    Replace it. It seals the oil passage to the lower tensioner. It should have a larger hole than that picture though
    '98 740il | 9/97 build | schwarz 2 | sandbeige | 5AT | 270k
    '04 330i ZHP sedan | Mystic blue | Alcantara | 6MT | 120k
    '00 540i sport | Titanium silver | Black | 5AT | 152k
    '85 Mustang GT convertible | Medium charcoal metallic | Gray | 5MT | 216k | one owner, all original

    mods: m-pars | Bilsteins & B&G springs | ValentineOne | StealthOne
    retrofits: full nav | MKIV | bluetooth TCU | BM53 w/ AUX input | video module w/ AV input & backup cam | oem sirius xm | xenon | shades | PDC | rain sensor | BMW DWS TPMS | lighted door handles | front seat heaters | heated steering wheel | euro rear fog lights | ski pass | folding mirrors


  4. #4
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    Reference RealOEM like it's a BMW bible!

    O-ring:
    https://www.realoem.com/bmw/enUS/sho...48#11141736758

    Always cross-check with a picture, since some of these part diagrams may be confusing. If RealOEM doesn't have a picture, then take the part number and search online.

    For example, FCP Euro:

    https://www.fcpeuro.com/products?utf...1-14-1-736-758
    Current: 2007 Z4 M Coupe (blue/black)
    Previous: 2001 740iL Sport (black/black), 2000 528i Sport (black/tan), 1995 318is (black/black), 1991 318is (white/black)

  5. #5
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    Quote Originally Posted by Ruskii View Post
    This might help:


    IMG_7545 (1).JPG
    Cute! I like the reply. How do you do that red circle?

  6. #6
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    Quote Originally Posted by racer2086 View Post
    Replace it. It seals the oil passage to the lower tensioner. It should have a larger hole than that picture though
    Strange, I have never seen a tensioner gallery seal with a restrictor plate. The '01 didn't have one, no does the M62tu I'm building. Can't recall seeing
    one in the others I've been in. Realoem shows just the seal. Very odd.

  7. #7
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    Quote Originally Posted by oldroller View Post
    Strange, I have never seen a tensioner gallery seal with a restrictor plate. The '01 didn't have one, no does the M62tu I'm building. Can't recall seeing
    one in the others I've been in. Realoem shows just the seal. Very odd.
    Indeed! Mine didnt have that plate either and Jerry's car is also '01.

  8. #8
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    Quote Originally Posted by Jerry Scholder View Post
    Cute! I like the reply. How do you do that red circle?
    If you have Windows on your computer, then use the Paint program. You can make basic shapes, add text, resize/flip images, etc.
    Current: 2007 Z4 M Coupe (blue/black)
    Previous: 2001 740iL Sport (black/black), 2000 528i Sport (black/tan), 1995 318is (black/black), 1991 318is (white/black)

  9. #9
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    Quote Originally Posted by oldroller View Post
    Strange, I have never seen a tensioner gallery seal with a restrictor plate. The '01 didn't have one, no does the M62tu I'm building. Can't recall seeing
    one in the others I've been in. Realoem shows just the seal. Very odd.
    What restrictor plate? Please explain as I don't know what this means.

  10. #10
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    Quote Originally Posted by Jerry Scholder View Post
    What restrictor plate? Please explain as I don't know what this means.
    Guys are talking about the "washer" like plate sitting behind the o-ring, which has a tiny hole in it. See the picture.

    IMG_7534.JPG

    When I did my guides, I also did not have this plate, only the o-ring. It's odd to see it there, given that we have similar cars. Plus, RealOEM and part places don't mention this plate, only the o-ring as a replacement.

    Given that all of us have only replaced the o-ring, I suggest leaving that plate out and replacing the o-ring.
    Current: 2007 Z4 M Coupe (blue/black)
    Previous: 2001 740iL Sport (black/black), 2000 528i Sport (black/tan), 1995 318is (black/black), 1991 318is (white/black)

  11. #11
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    I am a firm believer of if it aint broke don't fix it, put it back like you found it, because someone with more brains than us put it there.

  12. #12
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    There is no reference to a 'restrictor' for the tensioner gallery seal in Realoem, TIS, or any other sites/pages I can find.
    Restrictors serve a purpose in some cases, but not here.
    The big issue, imho, is the size of the hole, easily blocked resulting in loss of pressure to the tensioner.
    Take it out, replace the seal, and carry on.
    Timing cover.png

  13. #13
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    Maybe somebody did this job already and put back a wrong piece? This is some X-files level mystery

  14. #14
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    98 740il, 00 540i,04 ZHP
    I thought that was just a defect in manufacturing of the o-ring. Like the machine didn't stamp out one side of the o-ring. It surely should be open.
    '98 740il | 9/97 build | schwarz 2 | sandbeige | 5AT | 270k
    '04 330i ZHP sedan | Mystic blue | Alcantara | 6MT | 120k
    '00 540i sport | Titanium silver | Black | 5AT | 152k
    '85 Mustang GT convertible | Medium charcoal metallic | Gray | 5MT | 216k | one owner, all original

    mods: m-pars | Bilsteins & B&G springs | ValentineOne | StealthOne
    retrofits: full nav | MKIV | bluetooth TCU | BM53 w/ AUX input | video module w/ AV input & backup cam | oem sirius xm | xenon | shades | PDC | rain sensor | BMW DWS TPMS | lighted door handles | front seat heaters | heated steering wheel | euro rear fog lights | ski pass | folding mirrors


  15. #15
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    Is it possible we are looking for where it came from in the wrong place as I may have misled you? Thanks for the explanation. I did see around 5 different locations in realoem.com that it may have come from.

  16. #16
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    Oldroller's picture above is where that o-ring goes. There's only 1 place for it and it is in the passenger side head to the outside to seal to the passenger side upper timing cover to seal the oil passage that pressurizes the lower tensioner that screws in and out of the passenger side upper timing cover.
    '98 740il | 9/97 build | schwarz 2 | sandbeige | 5AT | 270k
    '04 330i ZHP sedan | Mystic blue | Alcantara | 6MT | 120k
    '00 540i sport | Titanium silver | Black | 5AT | 152k
    '85 Mustang GT convertible | Medium charcoal metallic | Gray | 5MT | 216k | one owner, all original

    mods: m-pars | Bilsteins & B&G springs | ValentineOne | StealthOne
    retrofits: full nav | MKIV | bluetooth TCU | BM53 w/ AUX input | video module w/ AV input & backup cam | oem sirius xm | xenon | shades | PDC | rain sensor | BMW DWS TPMS | lighted door handles | front seat heaters | heated steering wheel | euro rear fog lights | ski pass | folding mirrors


  17. #17
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    Quote Originally Posted by oldroller View Post
    There is no reference to a 'restrictor' for the tensioner gallery seal in Realoem, TIS, or any other sites/pages I can find.
    Restrictors serve a purpose in some cases, but not here.
    The big issue, imho, is the size of the hole, easily blocked resulting in loss of pressure to the tensioner.
    Take it out, replace the seal, and carry on.
    Timing cover.png
    Ordered a new seal/Oring and replaced. Thanks for the information.

    - - - Updated - - -

    Quote Originally Posted by racer2086 View Post
    Oldroller's picture above is where that o-ring goes. There's only 1 place for it and it is in the passenger side head to the outside to seal to the passenger side upper timing cover to seal the oil passage that pressurizes the lower tensioner that screws in and out of the passenger side upper timing cover.
    Thanks a lot for your information. Really appreciate the response to help me out.

    - - - Updated - - -

    Quote Originally Posted by georgebest View Post
    Maybe somebody did this job already and put back a wrong piece? This is some X-files level mystery
    Thanks everyone for weighing in on this. I did replace just the O ring without the plate at the designated location (new).

    - - - Updated - - -

    OP thinks this thread is now complete. Thanks everyone for the help.

  18. #18
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    Recently discovered the answer to this question. This O-ring and restrictor plate sits in the U shaped guide and seals against the block.





    Numbers one and two in the picture.
    2000 740i Sport | 2004 330xi | 1988 325i Vert | 2003 Z4 2.5 | 1995 Ford F150 | 2018 GTI

  19. #19
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    Wow very interesting. Looks just like the upper timing cover o-ring. Looks like the guide rail has the small bore in it, which makes me wonder why they bothered putting it on the o-ring?

    Also, in the context of the original post, I'm not sure how that would show up from taking off the water pump...
    '98 740il | 9/97 build | schwarz 2 | sandbeige | 5AT | 270k
    '04 330i ZHP sedan | Mystic blue | Alcantara | 6MT | 120k
    '00 540i sport | Titanium silver | Black | 5AT | 152k
    '85 Mustang GT convertible | Medium charcoal metallic | Gray | 5MT | 216k | one owner, all original

    mods: m-pars | Bilsteins & B&G springs | ValentineOne | StealthOne
    retrofits: full nav | MKIV | bluetooth TCU | BM53 w/ AUX input | video module w/ AV input & backup cam | oem sirius xm | xenon | shades | PDC | rain sensor | BMW DWS TPMS | lighted door handles | front seat heaters | heated steering wheel | euro rear fog lights | ski pass | folding mirrors


  20. #20
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    I didn't take a pic of the other side of the rail but I don't believe the aluminum casting has that small of a hole, so the "throttle plate" is added. I would guess that it fell out of the old guide upon removal, and landed somewhere hidden away until such time the water pump was removed.

    Funny, as soon as I noticed it I had to start searching for this thread.
    2000 740i Sport | 2004 330xi | 1988 325i Vert | 2003 Z4 2.5 | 1995 Ford F150 | 2018 GTI

  21. #21
    Join Date
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    98 740il, 00 540i,04 ZHP
    Damn good memory sir
    '98 740il | 9/97 build | schwarz 2 | sandbeige | 5AT | 270k
    '04 330i ZHP sedan | Mystic blue | Alcantara | 6MT | 120k
    '00 540i sport | Titanium silver | Black | 5AT | 152k
    '85 Mustang GT convertible | Medium charcoal metallic | Gray | 5MT | 216k | one owner, all original

    mods: m-pars | Bilsteins & B&G springs | ValentineOne | StealthOne
    retrofits: full nav | MKIV | bluetooth TCU | BM53 w/ AUX input | video module w/ AV input & backup cam | oem sirius xm | xenon | shades | PDC | rain sensor | BMW DWS TPMS | lighted door handles | front seat heaters | heated steering wheel | euro rear fog lights | ski pass | folding mirrors


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