- - Cracked Kona frame downtube
(https://www.bikeforums.net/framebuilders/1272502-cracked-kona-frame-downtube.html)
Andrew R Stewart
05-20-23 08:31 AM
Originally Posted by Breadfan
(Post 22895851)
So we are under the consensus that the tube cannot be replaced? Or, for economics sake, a sleeve would not hold up? I’m not too worried about the surface rust on the head tube. That’s all it is.
The tube can be replaced. It will not be inexpensive. It is only the owner who decides on the value as it is they who will pay. Sleeving the cracked area will also work but is also not cheap to do and has its own aspects that need to be done well. I would not sleeve this and would only consider replacing the tube if I had to keep this bike on the road. Andy
Breadfan
05-20-23 11:49 AM
Originally Posted by unterhausen
(Post 22896035)
A sleeve just introduces more problems.
Could you elaborate on that?
guy153
05-21-23 01:45 AM
Originally Posted by Breadfan
(Post 22895851)
So we are under the consensus that the tube cannot be replaced? Or, for economics sake, a sleeve would not hold up? I’m not too worried about the surface rust on the head tube. That’s all it is.
It could be replaced but idk how much it would cost if you had to pay someone to do that. My concern with a sleeve is that I think this crack is about where the butt ends. This means that the lower part of the sleeve would be welded (or brazed) onto the very thin part of the tube. Part of the reason it's so thin there is isn't designed to suffer the heat of welding (or even brazing). That's one of the reasons why you have butts in the first place. In fact the failure may have been promoted by that region getting overheated when all those cable guides and things were brazed on when the frame was made. The extra thickness of the sleeve and the heat would make a failure on the tube just below the new weld rather likely. Relying on something rather likely not happening is not good enough for something as safety critical as this.
If you replace the whole tube you're welding back onto the HT and the BB shell. These are both relatively much thicker metal and will be fine. You also have a small weld with the butted region at the bottom of the ST. But at least it's butted and it's only part of the weld.
Breadfan
05-21-23 02:32 AM
This is all very good to know and I appreciate everyone making me understand. I’ll just hang it up on my wall and I’ll wait for the right time to get it replaced.
