Repair frame with crack by seatpost clamp

Question

Is it feasible to repair a crack in a frame around the seatpost clamp? Being an aluminium frame I understand soldering is problematic. It doesn’t matter if seatpost is fixed in place as per a solution involving epoxy/some kind of wrap etc.

crack frames repair

David D · Accepted Answer

Is it feasible to repair a crack in a frame around the seatpost clamp?

feasible:
1. possible to do easily or conveniently.
2. likely; probable.

It is possible to repair an aluminum frame. It is not easy or convenient.

It's all about how much effort/money you are willing to put into this project.

Finding someone with a gas tungsten arc welding rig who would be willing to weld on your frame is one thing. Finding someone who knows what they are doing is something else.

Here is a discussion on a welding forum with an intelligent answer on aluminum bicycle frame repair. Here is a snippet of the conversation relating to repairing a frame:

Any repair should be made via gtaw (tig-heliarc) by an EXPERIENCED welder.  If the frame is truely 7005 then 5180 would be the filler material of choice.  This will allow the frame to undergo heat treatment to restore it to its original condition.    If the frame is actually a t6 alloy more than likely you should use a 4643 filler which again will allow heat treatment.....if you wish to repair without heat treatment use 5356 which will work on either alloy but without heat treatment it will never be in the condition it was when produced.

The most feasible solution is to see this as an excellent opportunity to upgrade.

yettsoman · Answer

It IS possible to repair this. It is possible to repair practically EVERYTHING that is man-made. Although it is impossible to say how cost-effective or how easy it will be by just looking at a couple of pictures, I would be confident that this frame could be repaired well and fairly cheaply. Yes, I'm one of those that hate the throw-away society we've become.

Answered by yettsoman on June 13, 2021

juhist · Answer

Is it feasible to repair a crack in a frame around the seatpost clamp? Being an aluminium frame I understand soldering is problematic

This is very typical of aluminum frames and in fact is the reason why I don't recommend aluminum frames (and forks) to be used. Instead, double butted chromium molybdenum steel (chromoly) wouldn't have this problem.
Aluminum has a finite fatigue life in contrast to steel that has an infinite fatigue life. The finite fatigue life means eventually after hard use a crack will appear, and start to grow.
Repair requires welding.
Welding an aluminum requires a new heat treatment after the welding in comparison to welding steel that doesn't. (Yet another reason why butted chromoly is better.)
A heat treatment requires putting the whole frame into an oven. This means you want to detach everything on the frame -- in fact, you want to remove the paint too. So you need to re-paint it after the heat treatment.
The expense of all this is so much that it will not be cost efficient. Since you need to anyway detach everything on the bike frame, it would be far easier to start looking for a new frame to attach your components to. Not only that, but if you repair an aluminum frame, the inherent flaw of aluminum that causes cracks to appear and propagate is still present. "It's a feature, not a bug." So the problem will repeat, perhaps after 10 000 km, perhaps after 100 000 km.
Make sure the new frame you purchase is butted chromoly and not aluminum so the problem won't repeat.

Repair frame with crack by seatpost clamp

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