Advertise on Bikeforums.net



User Tag List

Results 1 to 7 of 7
  1. #1
    Я люблю суп abarth's Avatar
    Join Date
    Jul 2008
    Posts
    1,248
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)

    Facing a Bottom Bracket

    What method do you use to check if the bottom bracket needs to be face? Is using a caliper to measure the length at various points on the bottom bracket a good enough method?

  2. #2
    just pokin' along desertdork's Avatar
    Join Date
    Aug 2008
    Location
    the desert
    Posts
    1,070
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Someone around here has suggested using a feeler gauge to determine if there are uneven distances between an external BB cup and the shell.

  3. #3
    Senior Member
    Join Date
    Apr 2009
    Location
    New Rochelle, NY
    My Bikes
    too many bikes from 1967 10s (5x2)Frejus to a Sumitomo Ti/Chorus aluminum 10s (10x2), plus one non-susp mtn bike I use as my commuter
    Posts
    21,552
    Mentioned
    51 Post(s)
    Tagged
    1 Thread(s)
    If the BB shell's rim has concentric tool marks made by the circular motion of a facing tool, then it's been faced and you don't need to do it again.

    When I see a BB that I'm not sure needs facing, I paint it with a magic marker, or toolmakers dye, then do a light pass with a facing tool. If it removes the dye over 270 degrees, it's fine and I don't have to face. Otherwise I face until I've achieved at least 300 degrees of face, which is needed for supporting cups flat. (low spots don't count, the cup is oriented by the high points of contact, so theoretically 3 areas forming a triangle would be sufficient)

    For a home mechanic, you can test by putting a thin grease film on the face or cup, and watching to see if it squeezes out evenly most of the way around. But if in doubt, a skim pass with a facer is to only definitive way to know.
    FB
    Chain-L site

    An ounce of diagnosis is worth a pound of cure.

    “Never argue with an idiot. He will only bring you down to his level and beat you with experience.”, George Carlin

    “One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN

    WARNING, I'm from New York. Thin skinned people should maintain safe distance.

  4. #4
    Senior Member
    Join Date
    Sep 2008
    Location
    Loveland, CO
    My Bikes
    Two LOOK 585s, one KG461
    Posts
    4,987
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Tighten the cups until they contact a .010 inch feeler gage, then use .008-.012 inch feelers to check for high or low spots. All paint should be removed from the faces of the BB shell before doing this.

  5. #5
    cab horn
    Join Date
    Jun 2004
    Location
    Toronto
    My Bikes
    1987 Bianchi Campione
    Posts
    28,295
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by FBinNY View Post
    If the BB shell's rim has concentric tool marks made by the circular motion of a facing tool, then it's been faced and you don't need to do it again.

    When I see a BB that I'm not sure needs facing, I paint it with a magic marker, or toolmakers dye, then do a light pass with a facing tool. If it removes the dye over 270 degrees, it's fine and I don't have to face. Otherwise I face until I've achieved at least 300 degrees of face, which is needed for supporting cups flat. (low spots don't count, the cup is oriented by the high points of contact, so theoretically 3 areas forming a triangle would be sufficient)

    For a home mechanic, you can test by putting a thin grease film on the face or cup, and watching to see if it squeezes out evenly most of the way around. But if in doubt, a skim pass with a facer is to only definitive way to know.
    Quote Originally Posted by DaveSSS View Post
    Tighten the cups until they contact a .010 inch feeler gage, then use .008-.012 inch feelers to check for high or low spots. All paint should be removed from the faces of the BB shell before doing this.
    I don't agree with the 300 degrees, unless it's a typo. It's an unbroken 360 degree ring that is the proper test of complete facing. The ring does not need to be the full width of the face. 300 degrees leaves 60 degrees left of a possible
    Last edited by operator; 07-12-10 at 10:52 AM.
    Mes compaingnons cui j'amoie et cui j'aim,... Me di, chanson.

  6. #6
    cab horn
    Join Date
    Jun 2004
    Location
    Toronto
    My Bikes
    1987 Bianchi Campione
    Posts
    28,295
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by abarth View Post
    What method do you use to check if the bottom bracket needs to be face? Is using a caliper to measure the length at various points on the bottom bracket a good enough method?
    Caliper tells you nothing. With a painted BB shell it's evident either by tool marks or removal of point that facing may have been done. If there's any doubt, measure the width and face it. Severe BB shell facing errors show up in bottom brackets after installation as binding all around/unusual spots. Or a BB that spins fine until it's fully torqued.
    Mes compaingnons cui j'amoie et cui j'aim,... Me di, chanson.

  7. #7
    Old fart JohnDThompson's Avatar
    Join Date
    Nov 2004
    Location
    Appleton WI
    My Bikes
    Several, mostly not name brands.
    Posts
    12,839
    Mentioned
    11 Post(s)
    Tagged
    0 Thread(s)
    Paint the faces with machinist's blue and run the facer over it lightly. If the bluing is removed unevenly, it needs facing.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •