Advertise on Bikeforums.net



User Tag List

Results 1 to 7 of 7
  1. #1
    Senior Member GrayJay's Avatar
    Join Date
    Sep 2009
    Location
    EagleRiver AK
    Posts
    1,229
    Mentioned
    2 Post(s)
    Tagged
    0 Thread(s)

    Fork Crown / steertube failure

    I recently converted a vintage Bottecchia road bike into a cyclocross bike, added cantilevers to the fork.

    http://www.bikeforums.net/showthread...=#post12603264

    Seward, AK April 2011 001.jpg

    After several miles of use, I noticed that something felt wierd with the steering and there was a mild shudder when braking. Then, rather unexpectedly the front brakes locked up and I flipped over the bars. Inspection revealed that the fork steer tube had separated from the cast fork crown, looked to be really insufficient factory brazing. I suspect that the shuddering cantilevers stressed the joint more than the original fork crown mounted centerpulls ever had. Nothing was actually bent or damaged in the crash (besides my hands), the crown was so loose I was able to remove it from the steer tube by hand. Once I cleaned away the scant remaining brass, the OD of the steering tube is 25.4mm and the ID of the cast hole in the crown is 26.0mm, makes for a really loose fit between the two. Is a 0.6mm loose fit at all typical at the fork crown? If I were to braze it back together and completely fill the void between the tube and crown with brass, should it hold together OK with such a large brazed gap or are there other measures I should take to fix?
    Last edited by GrayJay; 05-13-11 at 02:13 PM.

  2. #2
    Senior Member mudboy's Avatar
    Join Date
    Sep 2008
    Location
    Collegeville, PA
    My Bikes
    Ruckelshaus Randonneur, Specialized Allez (early 90's, steel), Ruckelshaus Path Bomber currently being built
    Posts
    1,354
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    That is not a typical gap, IMO. Should be a close sleeve fit, but not a press fit. Sounds like an ISO steerer and a JIS fork crown? Or was JIS 27.0?
    --~--~--~--~--~--~--~--~--~--~--~--~--~--~--~--~--
    Ruckelshaus Randonneur Ruckelshaus Path Bomber
    Flickr Photostream
    FrameBuilderSource.com Framebuilder Database

  3. #3
    Framebuilder
    Join Date
    Dec 2007
    Posts
    481
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Sounds like the caliper brake bolt had been holding things together, so when it was gone...
    If the steerer/crown was so badly brazed, I wouldn't trust the blade to crown joints either.
    New fork time.
    Last edited by Live Wire; 05-13-11 at 07:04 PM.

  4. #4
    Randomhead
    Join Date
    Aug 2008
    Location
    Happy Valley, Pennsylvania
    Posts
    12,730
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    ouch. I'm not sure it follows that the fork blades are a problem, but I would certainly have a hard time trusting it. It takes a lot of heat to braze a fork crown/steerer with brass. And it's not a job for a beginner.

  5. #5
    Senior Member bobbycorno's Avatar
    Join Date
    Sep 2007
    Posts
    2,545
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by mudboy View Post
    That is not a typical gap, IMO. Should be a close sleeve fit, but not a press fit. Sounds like an ISO steerer and a JIS fork crown? Or was JIS 27.0?
    AFAIK, 1" steerers are 25.4mm, regardless of headset dimensions. The 26.4/27.0 dimension is the diameter of the collar at the top of the crown. But it DOES sound like a mighty sloppy fit. I wouldn't trust it.

    SP
    Bend, OR

  6. #6
    Senior Member GrayJay's Avatar
    Join Date
    Sep 2009
    Location
    EagleRiver AK
    Posts
    1,229
    Mentioned
    2 Post(s)
    Tagged
    0 Thread(s)
    The crown casting does not have a collar around the steertube above the flat section of the casting. The race was held in place with a thin 26.4mm shim around the steertube. If I try to fix it, I will probably also add an external fillet around the steer tube to provide a bit stronger connection and cut it to correct 26.6mm size to retain the crown race without a shim.

  7. #7
    Senior Member
    Join Date
    Mar 2007
    Posts
    6,088
    Mentioned
    2 Post(s)
    Tagged
    0 Thread(s)
    That's way too much gap for my money. In your shoes, I'd either start over, or buy one of Soma's traditional cyclocross forks.

Posting Permissions

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