# Cracked weld question/possible repair



## JPS2345 (Jul 25, 2012)

Since this is probably the best source for people who understand the forces applied on bike frames, I was wondering if you could shed some light on why my frame cracked where it did, and if its safe to repair(I have a good friend who is a professional TIG welder).

This is a 2005 Giant Trance 4, I am running an in-spec fork(100mm) and the rear shock has been worked over by push, it mainly gets XC,Trail, and some very light AM style riding. Im about 240lbs ready to ride. If you need anymore details Ill be happy to add anything.

The broken weld







Zoomed out








Broken area highlighted in red


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## watts888 (Oct 2, 2012)

Alloy fatigue. It's a 2005 after all, and alluminum only has so many stress cycles. If you're friend is a good tig welder, and has the skills to do a proper post weld heat treatment, he could probably re-weld it and add a reinforcement gusset. Otherwise, maybe it's just time to get a new frame.


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## boots (Aug 15, 2008)

Two years ago i found a fatigue crack above the bottom bracket on my 2007 Intense 5.5. I prepped the crack and had it TIG welded by a professional then primed and painted it. I then sold it to a buddy and he has been riding it ever since without issue.
































Sent from my iPhone using Tapatalk


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## JPS2345 (Jul 25, 2012)

New frame is definitely the solution, I assumed the age was probably the culprit, but assumed it would have cracked in a different location than under there since there is a reinforcement above it. 

Do I need to have a copper slug made to slide down the seat tube to keep it from burning through and not allowing the seat post to go all the way down?


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## watts888 (Oct 2, 2012)

JPS2345 said:


> Do I need to have a copper slug made to slide down the seat tube to keep it from burning through and not allowing the seat post to go all the way down?


For this, I'd talk to your welder friend. tig welding heat is precise and accurate enough that he should be able to weld that area up without messing up the inside of the tube. As long as the weld is done without any stress of the frame (ie. depressurize the shock), should be good.


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## JPS2345 (Jul 25, 2012)

Im gonna strip it down to just a front triangle, one thought I had, would it be better to add some filler rod since those tubes are fairly thin already


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## watts888 (Oct 2, 2012)

Tig welding requires filler rod. A good welder can tig an aluminum pop can. If your friend is good, he can tig this. I'd tig the existing weld bead against the seat tube, and then add a new aluminum brace (probably a 90/45/45 degree flat 1/4" plate with a gap cut out in the 90-deg corner).


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## afwalker (Apr 26, 2012)

I wouldn't consider even touching this repair, but a good aluminum tig welder might but I hope he would insist on post-heat treating otherwise I doubt it would last as long as you would hope. Temper matters.
Aluminum Workshop: Achieving T6 designation for 6061 - TheFabricator.com
andy walker


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## bamwa (Mar 15, 2010)

according to bikepedia the frame is aluxx sl which is a 6000 series alum.

2005 Giant Trance 4 - BikePedia

ALUXX | Technology - Giant Bicycles | United States

6000 alum. needs different post heat treatment and filler rod than 7000 series.
http://www.sillygrin.co.uk/techstuff/service/easton/fab_instructions-7005_6061.pdf

But you can just weld the crack and see what happens also. Might last quite a while.


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