Bicycle Mechanics - 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.

http://lh5.ggpht.com/_ILaMONg0Xdk/TSqgxmfI6sI/AAAAAAAABs8/obDQz8ZSOuI/s640/110109%20Cannondale%20CAAD8%20Crack%204.jpg

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/CannondaleCAAD8Crack#

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

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.

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.

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!

Yea toss it, note to self, .. in future , you can fix steel.

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.

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.

I guess you could drill holes at the ends of the crack and sleeve it with carbon...

Toss it or take advantage of Cannondale's crash replacement policy. There is no cost-effective and safe way to repair your frame.

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

Please don't JB Weld it. That is a very dangerous idea.

That frame will never be safe to ride again.

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?

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.

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.

time for a new frame. I wouldn't ride it ! The crash replacement sounds like the best idea

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.

If you're going to ride that frame can I be the beneficiary on your life insurance policy?

If you're going to ride that frame can I be the beneficiary on your life insurance policy?

+1

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. :)

ZOMG. It'll go in the blink of an eye, dude.

Busted-open face in 3... 2...

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.

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.

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.

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?

Scrap dealer.

toegnix, My son has broken car and motorcycle parts welded into a free roaming sculpture...

Brad

Cut the rear triangle out, drill and tap a few holes into the seat and/or chain stays, and use some long bolts to make it into a stylie truing stand.

Or cut the whole frame lengthwise (through middle of head-tube, top-tube, down-tube, seat tube, and bottom bracket, and separate the left chain and seat stays from the right, and use each half as a wall hanging.

If you are bent (no pun intended) on riding that frame there is only one way to do a repair that will come close to providing original strength that is somewhat cost effective. It will also be ugly as hell and I would consider it temporary and limited duty.
Find a section of high strength alum tube long enough to cover the damaged area and extend 3 times the diameter of the damaged top tube on both sides of the damage. Cut a strip out of the new tube just wide enough to allow it to be worked over the damaged area.
Sand the ends to gradually "feather" their thickness towards the end edges. This will reduce stress risers at the ends of the patch piece.
Very thoroughly prep and clean the inside of the repair tube and damaged frame as well as drilling a small hole at each end of the crack. ( to inhibit propagation)
Coat the repair tube and frame with JB weld or similar high strength epoxy then work on the "patch" so the part from which you cut a strip is opposite the crack.
Clamp with hose clamps for several days while the bike is parked in a warm area and not used while the epoxy cures.
Keep in mind this would be considered an emergency/ temporary repair and I would only ride the bike sort term and very gently as I sought a replacement frame.
I assume no liability for the results of riding the above mentioned frame.

As you've concluded that it's probably a bad idea to ride it in it's current state, you might want to somehow render it completely unrideable (i.e., cut it in half), so it can't be used by an unsuspecting kid who finds it in the dumpster.

Drill the frame full of holes in the old-fashioned "weight reducing" method and see how little you can get it to weigh and keep it as a conversation piece.

Drill the frame full of holes in the old-fashioned "weight reducing" method and see how little you can get it to weigh and keep it as a conversation piece.

^^^ +1 Best idea yet!!

Good call. JB weld has no structural integrity to speak of. It just would have be a band aid over a wound.

use this frame as a donor frame and make a Bamboo bike.
http://build-its.blogspot.com/2010/09/building-bamboo-bike-frame.html

or donate it to me so I can make a bamboo bike.

use this frame as a donor frame and make a Bamboo bike.
http://build-its.blogspot.com/2010/09/building-bamboo-bike-frame.html

or donate it to me so I can make a bamboo bike.

Cool idea, but I have neither the time nor the patience. And I would consider donating it to you but shipping it to VA isn't economical at all.

Cut the rear triangle out and make it into a stool.

You guys underestimate the strenght of JB weld:
Tensile strenght:3960-PSI
Adhesion:1800-PSI
Flex :730-PSI
Shear:1040-PSI

With a 4 square inch patch,it would have 16,000 lbs of tensile strenght,plenty.You could fix the frame with JB if you HAD too.Get another one.

JB weld it and give it to Booger1.