# How to repair seat tube and top tube crack?



## febikes (Jan 28, 2011)

One of the local riders in my area has a crack in the seat tube and top tube of a three year old steel frame made by a major international brand. I think it was constructed in Taiwan and construction looks good. We prefer not to mention the brand because there is no point in turning this into brand bashing.

The frame is no longer covered by warranty and seems to be in good shape in other areas. From the way the crack developed I think the root cause was an overly flexible titanium seat post. The Ti Post also cracked as well. He was able to remove the post; the frame actually cracked a few months after the post cracked but my theory is that the two events are related.

I have not yet seen the frame in person. From the photo you can see what looks like a crack crossing the weld of the seat tube and top tube. It seems to also have a crack along the toe of the weld. The frame is cracked on both sides of the joint.

What types of repair techniques make sense here? Does it make sense to repair by stop drilling then TIG welding the crack and filling the stop drill holes?

Would welding a couple of small gusset top side and bottom side of the ST/TT joint also make sense?


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## Rody (Sep 10, 2005)

FEbikes,

A very common tube failure that has two contributing factors; an extended seat post that levers on the upper portion of the externally butted seat tube and the hardtail design that places forward pressure from the seat stays in the multi tubed junction.

The dynamic stress of the rider's weight constantly levering towards the rear of the bike compounded by the forward pressure of the stays create a hinge like fatigue that bulges the outer aspects of the tubing, resulting in the bi lateral failures.

Honestly, there is no clean repair other than removing the top tube and seat tube and replacing, a ton of work to salvage a frame unless it has historic or personal value to the owner, but an excellent opportunity for experience if you've not done such work before. Gussets and attempts to drill and weld the failure will only patch against the forces temporarily, as it will continue to propagate long term.

I've had one failure like this in a frame that was 4 seasons old and modified my seat tube design to protect against this in future builds.

The unfortunate truth is that all materials will fail eventually, designing and fabricating to offer the greatest probability of long term happiness and safety of our customers as they use our product should be our goal.

cheers,

rody


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## whydomylegshurt? (Jul 28, 2004)

Contact the manufacturer for a crash replacement. That is not an uncommon failure for that particular frame and they will give the owner a deal on a replacement. Have your buddy get a long seatpost so he has as much post in the frame as possible.


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## febikes (Jan 28, 2011)

Thanks Rody I totally agree and think the frame is going to become wall art or just go to recycling.


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## tamen00 (Mar 10, 2004)

whydomylegshurt? said:


> Contact the manufacturer for a crash replacement. That is not an uncommon failure for that particular frame and they will give the owner a deal on a replacement. Have your buddy get a long seatpost so he has as much post in the frame as possible.


This is a VERY VERY common failure for this particular frame - and the manufacturer is great at handling issues like this one. When I was riding this frame I had multiple of exactly the same failure (with a Thompson post extended way below the junction) and the manufacturer always took care of it.

Totally worth getting even the crash replacement on this one if it is out of warranty


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