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Hairline crack in my head tube - Aluminum Frame - Pics

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Hairline crack in my head tube - Aluminum Frame - Pics

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Old 04-23-08, 08:56 PM
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renlopez
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Hairline crack in my head tube - Aluminum Frame - Pics

I posted the same thread in the mechanics forum.

I took my mountain bike offroad for the first time in about 7 years. I noticed this crack in the head tube. I don't notice a difference in the ride or the steering. It's a 1996 Nishiki Backroads 7075 aluminum frame.

Is this something I should be worried about? If so, how worried?

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Old 04-23-08, 09:04 PM
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Originally Posted by renlopez View Post
Is this something I should be worried about?
yes
Originally Posted by renlopez View Post
If so, how worried?
very
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Old 04-23-08, 09:27 PM
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mcoine
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You shouldn't be worried at all since you will never be riding that bike again. And.. thats not a "hairline crack"
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Old 04-23-08, 09:33 PM
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Word.

Time to start afresh.
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Old 04-23-08, 09:58 PM
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You might find your answer here.
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Please dont outsmart the censor. That is a very expensive censor and every time one of you guys outsmart it it makes someone at the home office feel bad. We dont wanna do that. So dont cleverly disguise bad words.
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Old 04-23-08, 10:13 PM
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It can be repaired, but it might be hard to find someone that can do the repairs and it would probably cheaper to get a new frame.
Have a look at these before and after photos of repairs to head tubes:
http://www.gripsport.com.au/main.php?part=gallery&galID=16

Last edited by cobba; 04-24-08 at 10:04 AM.
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Old 04-23-08, 10:32 PM
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That crack = FAIL
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Old 04-24-08, 07:31 AM
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Before you go and ride that thing please make sure I'm listed as a beneficiary on your life insurance.
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Old 04-24-08, 07:47 AM
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Frame is done.
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Old 04-24-08, 09:00 AM
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DO NOT RIDE THIS BIKE. It's got one foot in the grave and the other on a banana peel. You will seriously F yourself up on the next jump or 2.
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Old 04-24-08, 10:13 AM
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7075 al is used because it is more easily machinable, because it is more brittle. The tensile strength is higher but for aluminum it's still easily machinable compared to steel. This means that the chip breaks quickly so you can hog more material off at a time, especially when boring a hole, which is great for making stuff. Brittleness, however, is not great for the end user. 7075 actually costs more pound for pound than 6061- twice as much, but the cycle times are reduced so much that manufacturing is cheaper in the end.

Because of the severe brittleness of your frame, you won't get much warning when it decides to break all the way. In fact I'm surprised (Godly intervention?) that it cracked like it did and didn't crack all the way through. I can tell by the photo, just from being a machinist and mechanical designer for so many years, that the head tube is WAY to thin for 7075 T6 by design.

It most likely chose to break when it did because while it was sitting you probably got some corrosion on your bearings or races making them ever-so-slightly uneven, which applied an uneven force to the head tube, which is real bad for brittle material. They probably tested the head tube with direct pressure in a lab, since if any indirect pressure from bad bearings would defer liability onto the bike owner.

So here's the easy answer: If you ride it you will die.

BTW Don't try to weld it. It cannot be fixed. The bottom of the head tube needs to be dead-flat or the bearings won't be under even pressure and you'll get another crack. You'll also lose the annealing (T6 most likely) the material was given once you apply the heat from welding, making it completely vulnerable to cracking. Even if you took all of that into consideration, you have to strip the paint to weld it . JB weld wont hold something like that together so don't try.

So you on the Darwin Award's page.....

Last edited by imcrushingyerhd; 04-24-08 at 10:19 AM.
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Old 04-24-08, 10:17 AM
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Wow. I get the message. Thanks.
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Old 04-24-08, 10:44 AM
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I think it's lucky you noticed this.....
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Old 04-24-08, 10:50 AM
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Boom, son. Yah done.
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Old 04-24-08, 11:49 AM
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This belongs in that ghetto thread about cracked pipes..
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