I didn't see the post you made that said the other side was cracked too. A truly skilled welder could safely weld the stay but I think you have some other issues involved. You must be one hell of a masher, don't doubt that you are and can put the torque to a frame. With both stays broken I'd rather not repair it to ride, take the components and other goods and build up a nice steel bike that suits your riding. Best of luck in whatever you decide to do.

Bill

A well-designed high-performance structure has one defining characteristic, that the entire structure is highly-stressed.

Most frames have higher and lower levels of material stress throughout the structure, so the highest-stresses areas will fail first while the balance of the structure will have accumulated fatigue degradation before failure.

It's known that aluminum has a more sharply-defined service life in terms of fatigue failure, as happened here.

This frame is literally worn-out in terms of fatigue-limit service life, and repairing it to go additional years is somewhat dangerous.
Any testing that was likely done before manufacture would have been given the quicker go-ahead if/when the first failure was relatively fail-safe as was the case here. Repairing it and continuing on with service would make failure of some less-failsafe part more likely, such as a head tube joint.
Welded aluminum frames have been heat-treated after welding, and re-welding without again heat-treating is just asking for more-rapid failure, not to mention the difficulty in maintaining alignment after welding both chainstays and in maintaining a round-enough bb shell after any welding was done at that junction.
This rider is large, and would be best advised to look for a newer frame imo, and it appears from the OP's post that such decision has already been made.

Patrik Tegnér reparing broken frames:
https://www.flickr.com/photos/5764199...th/5360366182/
https://www.flickr.com/photos/5764199...th/5304078741/

I repair aluminum frames all the time. Most commercially available 7005 chain stays are pretty thin and you can see a couple of fairly cold welds on that frame as well. With all due respect to other opinions, repaired frames seem to hold up quite well without a secondary age cycle.

If both the chain stays are cracked in the same place, they are too thin and should be replaced.

Most of what was said regarding "finite fatigue life" is true. I don't suggest you repair this frame. Mostly due to your size. Aluminum frames are made to be light and last long enough. Not forever.

frank- does it make sense to completly replace the tubes with new stronger ones?

in my eyes its not a repair then- but an upgrade/replacement

Yes, that would be ideal. There are only two 7005 tapered chain stays on the market. One is the Deda part and the other is the "open source" Easton profile. The one in this bike looks like the Easton part. The deda is very large. I have never seen either crack at the bridge when used in a road bike. (the same part is used for the MTB but curved) The deda would be the only option different than what is currently in place and while I have not seen any failures, they are so thin you can shine a light through them (kidding)

I would like to see the tubes, inside and out to see what happened. I build some special frames for criterium racing with stronger chainstays but it would look like it had "sausage legs" because they are very large.



So an assumption may be reached that either something went wrong with the welding or some other weird issue . Ill look at the pics again and we will talk more later.


Exactly.


Did you know your fork was aligned in a facility where sanitary manufacturing techniques are used to process aluminum frames? Have you had any symptoms of allergic reaction?

Life alert?

sounds like a very good upgrade- especially if he knows there is an issue- and he likes the frame he has.

"custom re-made for the owner" !

These sentences are significant.

How do "they" know how long is long enough?
Apparently TBB's bike didn't last long enough.

If theblackbullet is built like the German track stars, no aluminum frame is safe.

From the NY Times

Steel has a fatigue limit - a level of cyclic stress below which it will basically last forever. Aluminum has no such limit. All aluminum things will eventually fatigue crack. That's why airframes are inspected on a regular basis, and why aircraft manufacturers have quite elaborate methods for building and repairing them so as to minimize the risk of failure within the bounds of weight and cost imposed upon them. As others have said, you can certainly repair this frame. It will eventually fail again, somewhere. If you can't live with that, you shouldn't be using an aluminum frame. Love the color scheme, BTW.

welding a crack is a "FIX"
full replacement of the tubes with more heftier ones by someone qualified to make the call-
like Frank- is more of an "UPGRADE"

I have not. This must mean that aluminum frames are not the evil scourge they were purported to me to be. I shall no longer fear them. Thank you!

I hate to be the one to bring it up, but you might want to get a (gasp!) carbon frame. A good strong beefy one from a reputable manufacturer with a good lifetime warranty. Yes, I know, there's a special place in Colonel Lloyd's Hell for me for suggesting it, but CF doesn't fatigue at all ever.

If he was the original owner you are correct. If he is not the original owner, it lasted long enough for the original owner. That is a 50% average. Do you think there are 50% of the original simplex Delrin derailleurs remain, well never mind that example.

I found out there is another chain stay available from Nova cycles that is 2mm thick.

Jim, you are the "they" because you use aluminum handlebars and that makes you one of the people who buy aluminum tubes "damn the torpedos". Once you let the cat out of the bag it's pretty much a matter of time before you find an Alan dripping with Campy and you too will be enamored by the glow of polished aluminum tubing but this time it will be attached to dropouts. Will it matter?

Only time will tell..

Ha. I was thinking of "they" as the designers. "They" designed it to last long enough, but how do they know what long enough will be? Supposedly the original designed lifetime for the wonderful Austin-Healy 3000 was only 10 years. Now 60 years later people still drive and cherish them.

On the other hand there is the answer that Calvin's dad gave when Calvin asked how they knew the load capacity of a bridge - they drive heavier and heavier trucks over it until it collapses, then they weigh the truck and build another bridge exactly like the first one.

Um, I don't think I stress my aluminum handlebar so much. I'm just strong or heavy enough!

But I take your meaning.