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carbon fiber repair kit

Old 08-08-23, 02:31 PM
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carbon fiber repair kit

My Wilier had a stuck seatpost. Getting it out I used some serious force and manage to have a small crack wander down from the slit opening of the seatpost. It is not a full crack but you can see the stress as if the carbon torn a bit at the end of the U channel where the seatpost goes in. Structurally I don't think it is catastrophic but would like to use a carbon fiber repair kit to go over it and make is what I hope will be as strong as it was.
Has anyone used one of the kits? I watched a video of it on youtube and the kit cost $100. That seems like a lot given the frame is probably worth only about $300-350 if it was not damaged. It is a 2013 Grand Turismo but I like it because it has threaded BB. THe frame has about 18000 miles on it. Any thoughts or has anyone done this? Cheaper kits that do the same thing?
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Old 08-08-23, 03:11 PM
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Perhaps someone who knows what they're talking about with regard to carbon structures will chime in, but:

If it were my frame, I'd drill a hole at the bottom of the crack (that matches the diameter of the higher drilled hole), butter the seatpost with anti-seize paste and install it, and thereafter keep an eye on the crack.

This assumes that, with the saddle at the correct height, the seatpost extends a safe distance below the newly drilled hole.
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Old 08-08-23, 04:01 PM
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I just did a home repair with carbon fiber on a broken steel chainstay. I purchased a kit from ebay for about $40 and have plenty left over. A carbon frame will likely be easier to prepare and end up with a stronger repair than mine so I say go for it. Obviously, I am no expert but watch some YouTube vids and learn as much as you can. Some vids were a bit questionable but there are several from pro shops and CF suppliers. Main thing is to have the surface very, very clean and sanded down (watch the vids) to create extra grip for the repair and have everything you need all ready to go and organized. You'll see it recommended to use a vacuum wrap around the repair while it cures but some vids showed using electrical tape wound tightly which is what I did and came out surprisingly well. Pro repair shops can make it invisible but don't expect that on your home repair but it can still be very strong.
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Old 08-09-23, 12:39 PM
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I would just be aware of the failure mode of carbon. best analogy is an under ripe banana is hard to break the top to peel, but nick it with knife and it is easy. Anything that cuts into the carbon fiber introduces a week point

So you would need to think how the seatpost puts pressure on the affected area.

I also don't think the drill a hole to stop a crack works the same with carbon.

If you do try to repair do super good prep and absolutely use some type of pressure (vacuum bag, wrap with stretched old innertubes (cut in half) etc
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Old 08-09-23, 04:56 PM
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don't try this at home.
 
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My one year old 2014 carbon Bianchi developed a small crack in the end of the compression slot below the seatpost clamp. I think it's just in the paint. I took some photos to track any progression of the "crack". 35,000 miles later, there's no change at all.

Just get a couple of photos and check it periodically. It's likely okay.
Pull out the seatpost and look inside -- is the crack showing there too?
Even if it's structural, the clamp and seatpost inside the frame will keep it from failing suddenly. The post probably extends below the seat stays.

If the crack continues to extend, then a repair wrap of multiple layers around the frame would be good.

Last edited by rm -rf; 08-09-23 at 05:02 PM.
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Old 08-09-23, 06:22 PM
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I deal with Carbon Fiber daily and what you describe can be an easy fix with a strong shear strength epoxy filled into the crack and then smoothed before setting. The epoxy isn't cheap about $40 per tube of part A&B in a 50/50 mix. You will need to force the epoxy into the crack just hand pressure will work but it needs to be inside the crack. Each type of CF will have different shear strengths and depending on the pre-preg quality the final product will have a lot of different strengths. CF is cured in an oven at about 315 to 330 degrees. And it will delaminate above 350 degrees so it is a very temperature dependent material when in use.
It is hard to put another layer onto CF after the initial layer has been cured, because it takes the matrix material to merge at temperature to make the CF in the first place. Cold set matrix will likely separate upon some stress due to the differences in the way the material is cured. HTH, Smiles, MH
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