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Old 01-10-11, 03:23 PM   #1
toegnix
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Fix dented, cracking aluminum top tube

I'm looking for advice and potential vendors to fix a dented and cracked aluminum top tube.

I have a Cannondale CAAD8 aluminum frame that I crashed and dented the top tube with the handlebars a few years ago. I started riding the frame again last year and recently noticed it's starting to crack.



I want to keep riding this frame and would like to get an idea of how and how much to repair. I'm a NOT at all interested in making it look beautiful or light, just rideable.

Does anyone have experience with this? What solutions will work? Can you recommend a vendor (SoCal, preferably OC or LA county)?

More photos: http://picasaweb.google.com/toegnix/...aleCAAD8Crack#
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Old 01-10-11, 03:30 PM   #2
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toegnix, Try the framebuilders forum. If it were mine... recycle bin or a trip to the LBS for a replacement frame. While Cannondale warrantees their frames for life to the original owner WRT production issues I think there might be a discounted price for crash damage.

Brad
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Old 01-10-11, 03:40 PM   #3
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toegnix, Try the framebuilders forum. If it were mine... recycle bin or a trip to the LBS for a replacement frame. While Cannondale warrantees their frames for life to the original owner WRT production issues I think there might be a discounted price for crash damage.

Brad
^^^^
I would think that the repair would out-cost a replacement since a new caad 8 complete bike is $900.
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Old 01-10-11, 03:47 PM   #4
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C'dale will sell you a replacement frame.

Or go to an aluminum Welder, welding shop ..
they can lay a bead down, after prepping that crack.
and or a patch welded on, over that area, double the wall thickness
where you banged the handlebars into that spot in the crash.
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Old 01-10-11, 04:08 PM   #5
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The reason the frame cracked is because of the heat treating that was done to make the very thin tubing stronger (higher yield strength and higher fatigue strength), so it retains alignment and lasts longer during hard use.
However, heat-treated aluminum cannot be dented without introducing precurser cracks, and is thus no longer malleable.

Any welding done after heat-treating will return the metal to it's original, weak state.
If this frame doesn't use butted tubing, there is some excess of strength along the mid-sections of each tube, and the heat treating was done firstly to strengthen the ends, where the stresses are highest. Whether or not the middle of each tube is thick enough to retain sufficient strength after welding would be very hard to calculate however, and cracks anywhere in a heat-treated frame tend to spread rapidly in brittle (sometimes spectacular) fashion.
I've seen and heard Cannondale frames snap in two, with a bang, the metal is that brittle!

Last edited by dddd; 01-10-11 at 04:17 PM.
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Old 01-10-11, 04:23 PM   #6
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Yea toss it, note to self, .. in future , you can fix steel.

Last edited by fietsbob; 01-11-11 at 02:18 AM.
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Old 01-10-11, 04:53 PM   #7
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The reason the frame cracked is because of the heat treating that was done to make the very thin tubing stronger (higher yield strength and higher fatigue strength), so it retains alignment and lasts longer during hard use.
However, heat-treated aluminum cannot be dented without introducing precurser cracks, and is thus no longer malleable.

Any welding done after heat-treating will return the metal to it's original, weak state.
This. ^

The only plausible way to safely repair the frame would be to cut out the whole tube, weld in a replacement, and re-heat-treat the entire frame. The cost of doing this would likely approach that of a brand-new replacement frame.
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Old 01-10-11, 05:35 PM   #8
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This. ^

The only plausible way to safely repair the frame would be to cut out the whole tube, weld in a replacement, and re-heat-treat the entire frame. The cost of doing this would likely approach that of a brand-new replacement bike.
^fixed.

New frames of similar quality are dirt cheap, and if you want to stay with Cannondale they have a crash-replacement program. Unless you are an experienced aluminum tig welder and posses equipment ready to do the heat treatment then a proper repair will almost definitely be more expensive than buying a replacement frame.
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Old 01-10-11, 10:50 PM   #9
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I guess you could drill holes at the ends of the crack and sleeve it with carbon...
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Old 01-11-11, 08:36 AM   #10
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Toss it or take advantage of Cannondale's crash replacement policy. There is no cost-effective and safe way to repair your frame.
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Old 01-11-11, 11:37 AM   #11
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If you want to experiment, use J-B Weld (from hardware or autoparts store). It may stop or slow cracking from spreading. You can fill the dent and wrap J-B Weld with blue masking tape until dry. It's gray color after mixing. Make sure you follow a direction, like prep that surface (remove paint), etc...
http://jbweld.net/products/jbweld.php
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Old 01-11-11, 12:07 PM   #12
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Please don't JB Weld it. That is a very dangerous idea.

That frame will never be safe to ride again.
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Old 01-11-11, 12:23 PM   #13
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Please don't JB Weld it. That is a very dangerous idea.

That frame will never be safe to ride again.
Please educate me. Does it take any thing away? it's bonded. Is it weak the frame?
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Old 01-11-11, 12:42 PM   #14
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I've thought about repairing cracks in tubing by filling the tube with something like epoxy or a melted polymer.

The substance would have to have the right strength and rigidity.
For smaller diameter tubes the "resin" could be high-density, whereas for a large-diameter tube it could be dispensed as a foam, with some volume percentage of air.

I've used engineering resins for "potting" of electrical circuits, both for vibration resistance and water exclusion. The resins can be custom-tailored to the customer's needs.

Unfortunately, there seems to be no data on what has worked for a bicycle frame.

Also, any bandage-type repair has to take into consideration the possibility of excessive stress concentration where the bandage ends and the original structure takes over, so the repair material has to have flexibility via some combination of material properties and tapering of the thickness. Lastly, some degree of bond adhesion would likely also be a factor in any such repair's durability.

Overall then, designing a repair is more complicated than it first seems. Doubly so in the case of high-performance (i.e. lightweight) structures.
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Old 01-11-11, 12:55 PM   #15
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Please educate me. Does it take any thing away? it's bonded. Is it weak the frame?
I do not think JB weld will make the frame any worse, but the idea of using it for frame repair is nonsense. JB weld is just an epoxy and has nowhere near the strength of a proper welded joint or the original tube. Nowhere near meaning like less than 1/100th the strength, if you are lucky.

You would be better off just getting a skilled aluminum welder to put a patch over it... but that ist't too good either.
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Old 01-11-11, 01:29 PM   #16
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time for a new frame. I wouldn't ride it ! The crash replacement sounds like the best idea
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Old 01-11-11, 01:39 PM   #17
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Also, let's not forget that welding aluminum causes significant distortion in the tubing after the weld has cooled, not to mention the related residual tension stress which further greatly weakens the structure. Only re-heat-treating will cure the loss of strength and stress-relieve the welded region.

LarDasse has it right, JB Weld won't fix the crack.
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Old 01-11-11, 03:39 PM   #18
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If you're going to ride that frame can I be the beneficiary on your life insurance policy?
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Old 01-11-11, 04:34 PM   #19
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If you're going to ride that frame can I be the beneficiary on your life insurance policy?
+1
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Old 03-27-11, 10:53 PM   #20
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Looked into carbon sleeving and aluminum fixes and both weren't worth it.

I've gotten another 1,000 miles on it but the crack has grown. Probably another 30-60 days before I retire it.
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Old 03-27-11, 11:11 PM   #21
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ZOMG. It'll go in the blink of an eye, dude.

Busted-open face in 3... 2...
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Old 03-28-11, 05:37 AM   #22
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It's a thin walled aluminum tube, the crack will propagate. There are no plugs or fillers or sleeves that will prevent that crack from propagating. You may be able to prevent a catastrophic failure at that location, but the crack will spread and the top tube will crack elsewhere.

I strongly suggest you stop riding that frame, but if you refuse to yield to common sense at least keep a close watch on that area while you're riding. You might get some sort of hints just before eminent failure like rapidly spreading crack, or even creaking sounds.
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Old 03-28-11, 07:59 AM   #23
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Quote:
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I've gotten another 1,000 miles on it but the crack has grown. Probably another 30-60 days before I retire it.
I'd put a fair bet on it not lasting another 30-60 days if you ride it. The fact the crack has continued to propagate should really tell you something important.
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Old 03-28-11, 08:42 AM   #24
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Holy spit you should stop riding that. It has already failed. The only thing you are waiting for now is for the tubes to neatly separate themselves for easier disposal.
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Old 05-18-11, 09:02 AM   #25
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UPDATE: I stopped riding it about two weeks into April. The crack grew enough that it started to worry me. The bike currently hangs in the garage, waiting for me to strip it and transfer everything to another frame I have waiting.

So now, what are some good ideas for the frame? Anyone want to buy it for some reason? eBay? Make a lamp out of it? Trash?
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