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Old 04-08-06, 05:18 PM   #1
Eatadonut
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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?
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Old 04-08-06, 06:12 PM   #2
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JB weld is not going to solve your problem.
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Old 04-08-06, 06:37 PM   #3
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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.
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Old 04-08-06, 08:05 PM   #4
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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
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Old 04-08-06, 08:11 PM   #5
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i saw it on ebay as well. i wouldn't try it.
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Old 04-08-06, 09:37 PM   #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.
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Old 04-08-06, 10:26 PM   #7
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Ah, an ebay special. Don't buy into someone else's problem.
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Old 04-09-06, 10:56 AM   #8
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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.
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Old 04-09-06, 11:40 AM   #9
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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?
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Old 04-09-06, 12:34 PM   #10
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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?
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Old 04-09-06, 12:40 PM   #11
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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?

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.
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Old 04-09-06, 06:22 PM   #12
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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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Old 04-09-06, 10:33 PM   #13
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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.
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Old 04-09-06, 11:15 PM   #14
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What do you prefer, a pretty bike or a pretty face?
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Old 04-09-06, 11:18 PM   #15
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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
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Old 04-10-06, 02:15 AM   #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?
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Old 04-10-06, 02:42 AM   #17
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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...
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Old 04-10-06, 06:52 AM   #18
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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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