frame stress cracks

Questions about purchasing bicycles and parts

frame stress cracks

Postby reparto corse » Wed Feb 21, 2007 9:45 pm

Hi All,
i was wondering if anyone here has had any experience with stress cracks appearing on their frames. I ask this as i haven't seen one before. what are the characteristics to look out for? Are the symptoms symilar in different materials ie. carbon, alloy and cromoly do the symptons appear the same in each material? If one discovers cracking what can be done about it? How does one test for cracking? If anyone has any knowledge on this topic, it would be very appreciative if you could shed some light on the matter.
I ask this as i recently bought a frame on ebay, after cleaning her i noticed what looked like a hair line crack in the paint. maybe it's just paint crack, then again maybe not.

cheers
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by BNA » Wed Feb 21, 2007 9:54 pm

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Postby heavymetal » Wed Feb 21, 2007 9:54 pm

What material is the frame and where about is the crack?

Different materials usually crack in different places. I had a relatively new aluminium frame a few years ago crack around the welds, but I had a steel one crack and break on the chain stays.

There is a picture at the bottom of this page with a cracked alloy frame and his temporary repair :D

http://www.lunky.com/viewday.php?l=2-11-2003&page=3
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Postby reparto corse » Wed Feb 21, 2007 10:17 pm

The material is aluminium, the crack is at the very tip of the weld, not on the weld but rather where the tubing meets the weld. It's very fine, I wouldn't have even noticed it if the grease buildup hadn't seaped into it.
It's located on the downtube about 3 inchs before it meets with the head tube. There are two triangle wedges that are welded on to both the head tube and the down tube, one on iether side. This crack appears at the end of one of these support wedges.
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Postby sogood » Wed Feb 21, 2007 10:25 pm

reparto corse wrote:The material is aluminium, the crack is at the very tip of the weld, not on the weld but rather where the tubing meets the weld. It's very fine, I wouldn't have even noticed it if the grease buildup hadn't seaped into it.
It's located on the downtube about 3 inchs before it meets with the head tube. There are two triangle wedges that are welded on to both the head tube and the down tube, one on iether side. This crack appears at the end of one of these support wedges.

That sounded bad. Common location of damage from frontal impact. :(
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Postby heavymetal » Wed Feb 21, 2007 10:27 pm

Aluminium always ends to crack at the weld points. It may only be a crack in the paintwork if it's very fine, but it usually indicates some movement if the paint has cracked.

You may be able to get an aluminium welder to re-weld it, but if its a fine crack I'd leave it and see what develops. It all depends on what you are using the bike for. The fact that it's cracked at the gussets, may indicate that it's had a hard life.

My aluminium bike had corrosion (looked like rust) in the cracked weld, which is how I spotted it. It was an MTB and the crack got longer, so I threw the frame out in the end as it wasn't worth the trouble fixing it and the cracked weld was in the down tube near the bottom bracket.
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Postby Mulger bill » Wed Feb 21, 2007 10:30 pm

The base of a gusset is not a nice place for a crack, the gusset is there because it's a high stress area.

There's a place in Vic called Gripsport who can repair alloy frames, I've seen an MTB with a cracked and flared headtube that was fixed by them, the owner said it was way stiffer than before.
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Postby reparto corse » Wed Feb 21, 2007 10:48 pm

looks like i'll have to get it xrayed, would be a shame if it is cracked as it's a nice frame. It definatly whasn't treated with the respect it deserved.
looked like it never had been degreased, with the amount of grease stains that i had to buff out on the chain stays.

do you know how much it cost the bloke to have his frame repaired? mulger bill.
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Postby Mulger bill » Wed Feb 21, 2007 11:45 pm

Sorry, no.

I was too busy trying to keep the lungs inside, he was getting ready to hit the hill in the right direction. And laughing at the old bastard :x

It was a mud brown Kona hardtail if that helps :?
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Postby reparto corse » Thu Feb 22, 2007 5:41 pm

Thanks guys for your input i really appreciate it.
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