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  1. #1
    You know you want to. Eatadonut's Avatar
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    Headtube stress and cracks

    Say I have a Pinarello Paris frame with a bit of a crack in the headtube. JB weld can be used on aluminum, but I don't know what kind of pressure the headtube is under. Is this asking for a concrete faceplant?

    If I wrapped a pipe clamp around it, would that hold it?
    Weather today: Hot. Humid. Potholes.

  2. #2
    You need a new bike supcom's Avatar
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    JB weld is not going to solve your problem.

  3. #3
    Senior Member Retro Grouch's Avatar
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    Quote Originally Posted by Eatadonut
    Say I have a Pinarello Paris frame with a bit of a crack in the headtube. JB weld can be used on aluminum, but I don't know what kind of pressure the headtube is under. Is this asking for a concrete faceplant?

    If I wrapped a pipe clamp around it, would that hold it?
    Are you seriously talking about riding a Pinarello Paris that has JB weld and a hose clamp holding the head tube together? Now there's a visual to make me smile.

  4. #4
    Senior Member concernicus's Avatar
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    doesnt matter. just ride.
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    it would be wise to get a new frame, or, if you can, have a local framebuilder fix it up for you

  5. #5
    Senior Member barba's Avatar
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    i saw it on ebay as well. i wouldn't try it.

  6. #6
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    The only safe "repair" for a cracked headtube is replacement. The headtube is under a lot of stress during braking, cornering and from bumps in the road and is too vital to the control of the bike to ever be compromised.

  7. #7
    You need a new bike supcom's Avatar
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    Ah, an ebay special. Don't buy into someone else's problem.

  8. #8
    You know you want to. Eatadonut's Avatar
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    What a bunch of party poopers

    I may buy it anyway because it's gorgeous, though I wish it had curves like the new ones.

    I'm convinced there's a way to repair aluminum reliably, even if it's ugly. I'll figure it out eventually.
    Weather today: Hot. Humid. Potholes.

  9. #9
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    Quote Originally Posted by Eatadonut
    What a bunch of party poopers

    I may buy it anyway because it's gorgeous, though I wish it had curves like the new ones.

    I'm convinced there's a way to repair aluminum reliably, even if it's ugly. I'll figure it out eventually.
    We hate to rain on your parade but you did ask.

    Sure there is way to repair Al reliably. It's called Heliarc welding followed by suitable heat treatment. The question is is the cost worth it?

  10. #10
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    heh, like that info would fit here...
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    You can zip it up with a clean weld and then hang it to 'cure' for about 6 months to a year. Then you've only got about a 30% chance of catastrophic failure when riding it fast down a hill in traffic. You a gambling man?

  11. #11
    You know you want to. Eatadonut's Avatar
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    Quote Originally Posted by r-dub
    You can zip it up with a clean weld and then hang it to 'cure' for about 6 months to a year. Then you've only got about a 30% chance of catastrophic failure when riding it fast down a hill in traffic. You a gambling man?

    Sounds good. I think i'll back up the weld with elmer's glue. It just seems like such a waste to let a beautiful frame die because of 1/2" of material that's cracked.
    Weather today: Hot. Humid. Potholes.

  12. #12
    Gone, but not forgotten Sheldon Brown's Avatar
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    Quote Originally Posted by Eatadonut
    Say I have a Pinarello Paris frame with a bit of a crack in the headtube. JB weld can be used on aluminum, but I don't know what kind of pressure the headtube is under. Is this asking for a concrete faceplant?
    The photos on eBay aren't clear, but I've seen aluminum frames with vertical cracks along the head tube caused by problems with headset installation.

    The risk is that the crack ends at a sharp "stress riser." It's sorta like a cellphane potato chip bag...as long as the edges are flat, it's super strong, but once a tear starts, it takes very little to make it grow.

    If you do buy this frame, it would be a good idea to drill a "stopper hole" at or just below the end of the crack. This can get rid of the stress riser so the crack won't be so likely to grow.

    Given the nature of headsets and frame stresses, I don't believe this would be particularly dangerous to ride. You should certainly keep an eye on it to see if the crack is growing, but I would expect that the worst that might happen would be that the headset would become somewhat loose, gradually over time. I don't see this causing a sudden failure and crash.

    If I didn't already own too many bikes I'd be tempted by it myself...the price is right, and I've always had a weakness for red bikes...

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  13. #13
    Senior Member spunkyruss's Avatar
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    Quote Originally Posted by Sheldon Brown
    .....The risk is that the crack ends at a sharp "stress riser." It's sorta like a cellphane potato chip bag...as long as the edges are flat, it's super strong, but once a tear starts, it takes very little to make it grow.....
    I have never heard a better description of a stress riser.

    I also agree that the bike may still be usable.

  14. #14
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    What do you prefer, a pretty bike or a pretty face?

  15. #15
    You know you want to. Eatadonut's Avatar
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    Quote Originally Posted by ivan_yulaev
    What do you prefer, a pretty bike or a pretty face?
    Even if I had a pretty face to begin with, the answer is always pretty bike. Nice try though
    Weather today: Hot. Humid. Potholes.

  16. #16
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    Why would you hang the bike for 6 months to cure? After the metal has cooled, what more could possibly happen?

  17. #17
    Senior Member DannoXYZ's Avatar
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    Without post-weld heat-treatment, aluminium takes many months to harden back up to full-strength. But it requires stressing it, not hanging it on a wall... You'll see a lot of "artificially age-hardened" when it comes to aluminium...

  18. #18
    Senior Member capwater's Avatar
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    All this talk about welds and stress fractures and clamps, etc is just overkill. All ya need is a couple of wraps of duct tape and you'll be good to ride the Giro.

    Serious note: bike riding, especially FAST bike riding/racing carries with it inherent risks of body damage (here's praying for buddy Saul Raisin). Why compound those risks with a known physical defect to your frame? Broken bones and injury at any price aren't a deal.

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