Heavy Rider - BB Threads Stripped?

Discussion in 'Cycling Equipment' started by (PeteCresswell), Feb 24, 2006.

  1. I just toasted the drive side threads on my FS's BB. No cross threading,
    they're just sheared off all around.

    Happened sometime during the course of a three-hour ride.

    Now that I think of it, I went around and around with a previous bike's maker
    because I thought they had tapped the BB shell off-center. i.e. the threads
    were very shallow (or sheared off?) in on part of the shell. A trip though it
    with a thread chaser seemed to help a little - and the thing never failed in
    use.


    Could a heavy rider tear these threads out? The older bike was Alu and the
    latest one's BB shell is magnesium.

    No previous problems with the BB. Torqued to spec and all that.
    --
    PeteCresswell
     
    Tags:


  2. Werehatrack

    Werehatrack Guest

    On Fri, 24 Feb 2006 10:06:51 -0500, "(PeteCresswell)" <[email protected]>
    wrote:

    >I just toasted the drive side threads on my FS's BB. No cross threading,
    >they're just sheared off all around.


    The threads in the BB shell of the frame, or the threads on the BB
    itself?

    >Happened sometime during the course of a three-hour ride.
    >
    >Now that I think of it, I went around and around with a previous bike's maker
    >because I thought they had tapped the BB shell off-center. i.e. the threads
    >were very shallow (or sheared off?) in on part of the shell. A trip though it
    >with a thread chaser seemed to help a little - and the thing never failed in
    >use.
    >
    >
    >Could a heavy rider tear these threads out?


    Although I would not ordinarily expect this to be possible, I suppose
    that a brittle thread material might be subject to shearing if a heavy
    rider did a lot of standing to pedal on the bike, but if the failure
    mode is what I'm thinking about, the BB would need to be able to move
    around a bit in order to do this. Since you state that the threads
    had been chased with a tap, I think there's a possibility that the
    original problem that caused the threads to need chasing may have
    contributed to the eventual failure by permitting the BB to squirm in
    the shell.

    > The older bike was Alu and the
    >latest one's BB shell is magnesium.


    Ugh. Magnesium. In my opinion, this is part of the problem. Usage
    of any significant amount of Mg in an aluminum alloy makes the metal
    much more susceptible to cracking.

    >No previous problems with the BB. Torqued to spec and all that.


    Looks like your best option is probably to find one of the threadless
    BB cartridges.
    --
    Typoes are a feature, not a bug.
    Some gardening required to reply via email.
    Words processed in a facility that contains nuts.
     
  3. M-gineering

    M-gineering Guest

    Werehatrack wrote:

    >
    > Looks like your best option is probably to find one of the threadless
    > BB cartridges.


    ream and tap Italian!
    --
    ---
    Marten Gerritsen

    INFOapestaartjeM-GINEERINGpuntNL
    www.m-gineering.nl
     
  4. Per Werehatrack:
    >Although I would not ordinarily expect this to be possible, I suppose
    >that a brittle thread material might be subject to shearing if a heavy
    >rider did a lot of standing to pedal on the bike, but if the failure
    >mode is what I'm thinking about, the BB would need to be able to move
    >around a bit in order to do this. Since you state that the threads
    >had been chased with a tap, I think there's a possibility that the
    >original problem that caused the threads to need chasing may have
    >contributed to the eventual failure by permitting the BB to squirm in
    >the shell.
    >
    >> The older bike was Alu and the
    >>latest one's BB shell is magnesium.

    >
    >Ugh. Magnesium. In my opinion, this is part of the problem. Usage
    >of any significant amount of Mg in an aluminum alloy makes the metal
    >much more susceptible to cracking.


    Talked to the local dealer - who rode the same bike I have for several years.
    He concurred that the mag is prone to stripping out - even kept a spare link
    around for himself, and he only weighs about 180.

    >
    >>No previous problems with the BB. Torqued to spec and all that.

    >
    >Looks like your best option is probably to find one of the threadless
    >BB cartridges.


    I think my first move is going to be to see if Maverick will sell me one of
    their links - which appear tb made of something more robust than the magnesium
    that Seven's are made from.

    I'll Google "threadless BB cartridge".... that concept was what came to mind
    first... just didn't know if an implementation existed.
    --
    PeteCresswell
     
  5. Per Werehatrack:
    >Since you state that the threads
    >had been chased with a tap,


    Separate issue. I was describing a situation on a previous bike.
    --
    PeteCresswell
     
Loading...
Loading...