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Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

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Old 05-14-12, 10:31 PM   #1
bobotech
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Crack on bottom bracket, is it dangerous?



You can see the crack, circled in red.

Is this dangerous?

In a nutshell, Schwinn will warranty the frame however they want me to destroy the bike which is fine with me. However my 22 year old son does not want me to destroy the bike in exchange for the new one. He feels that the crack is insignificant and not worth worrying about. He doesn't want the red replacement bike that Schwinn offered us.

Ugh.

So tell me, is this a dangerous crack?
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Old 05-14-12, 11:22 PM   #2
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I would replace it, particularly since Schwinn is providing a free replacement. Send it out to get painted if the color is a problem.

My guess is that your crack will only get worse. I don't know that I'd call it "dangerous" the way I would a fork crack but it will fail.
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Old 05-15-12, 12:39 AM   #3
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Hard to tell if it's really a crack, or an original imperfection in the BB shell. It has a bit of an "always been there" look to it.

Also, why does your FD cable seem to have a strage bend in it ?
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Old 05-15-12, 12:51 AM   #4
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To find out if it is a crack or just an imperfection you would need to grind that bb down a little to see how far it penetrates... as for the skewed cable angle...that might stem from a slightly skewed cable guide.
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Old 05-15-12, 02:19 AM   #5
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Couldn't he pull the crank out too to see if crack goes through to the inside?
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Old 05-15-12, 03:05 AM   #6
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I take it there was something that led you to inspect the bottom of the bb and led you to determine it was cracked ? At first and even to this point I tend to lean towards it not being a crack from the bend or round of the mark. I mean, a crack is usually one direction and a straight fault line ? That mark starts in at one angle from the edge and then makes a rounded turn.
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Old 05-15-12, 04:46 AM   #7
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I'd take out the bb and look the shell from a profile angle to see if the crack is real and deep or just an imperfection.
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Old 05-15-12, 06:18 AM   #8
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+1, and no i doubt the ibke will explode with a crack in that area, the worse case scenario is that the BB will start creaking and at some point the driver side cup will get lose. Well the crack might spread up to the other side of the BB shell too.

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To find out if it is a crack or just an imperfection you would need to grind that bb down a little to see how far it penetrates... as for the skewed cable angle...that might stem from a slightly skewed cable guide.
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Old 05-15-12, 07:10 AM   #9
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Well yes, it is a crack. I took the bottom bracket out and looked inside and the crack is present on the inside of the bottom bracket shell wall.
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Old 05-15-12, 08:10 AM   #10
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I was going to say take the paint off, but seeing the same crack line,
on the inside seems to confirm.. I suspect welding up the crack
and having the BB re machined makes no economic sense..

so cut up the frame, as scrap metal.
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Old 05-15-12, 08:25 AM   #11
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Quote:
Originally Posted by bobotech View Post
Well yes, it is a crack. I took the bottom bracket out and looked inside and the crack is present on the inside of the bottom bracket shell wall.
Cracks on things that are repeatedly stressed inevitably spread. You need another frame.

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Old 05-15-12, 08:28 AM   #12
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You need another frame.
+1.
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Old 05-15-12, 08:42 AM   #13
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Absolutely warranty the frame. Ignore the kid and get a frame that structurally sound. Spray paint is cheap. If he's that bothered about the color let him repaint it.
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Old 05-15-12, 09:08 AM   #14
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Quote:
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Well yes, it is a crack. I took the bottom bracket out and looked inside and the crack is present on the inside of the bottom bracket shell wall.
Put a fork in that frame... it's done.
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Old 05-15-12, 10:55 AM   #15
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That is totally what I thought I would hear. And I am going to just re-explain to the kid just how big of a deal this is.

Really cool thing is that Schwinn went and emailed me back this morning saying that they found another bike that maybe has a color that he would like better and I'm going to show him. Its a bit of an upgrade as well which is cool.
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Old 05-15-12, 11:11 AM   #16
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You're being offered a new frame and you're questioning the merits of the defect based on what your 22 year old son has to say about it? I was an idiot when I was 22, figured I was invincible, can't imagine he's any different. I'd jump on an opportunity to trade my all frames in for free for a new paint refresh, let alone a repair.

Tell your son he'll understand when he's older.
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Old 05-15-12, 11:17 AM   #17
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You're being offered a new frame and you're questioning the merits of the defect based on what your 22 year old son has to say about it? I was an idiot when I was 22, figured I was invincible, can't imagine he's any different. I'd jump on an opportunity to trade my all frames in for free for a new paint refresh, let alone a repair.

Tell your son he'll understand when he's older.
I totally and one hundred percent agree with what you said. You summed it perfectly.

My son just thinks I'm an anal overly detailed minded nutcase who doesn't know everything. He doubts me every way he can and he is stubborn as a mule. I just want to scream sometimes.
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Old 05-15-12, 01:49 PM   #18
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I would replace it, particularly since Schwinn is providing a free replacement. Send it out to get painted if the color is a problem.
+1 this.

If you really think this is a cosmetic flaw, pull out the bottom bracket cups and see if the crack extends through the full thickness of the shell. If it does, it's time for replacement.
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Old 05-15-12, 05:10 PM   #19
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My son just thinks I'm an anal overly detailed minded nutcase who doesn't know everything. He doubts me every way he can and he is stubborn as a mule. I just want to scream sometimes.
Well, there is a cure for both of your problems; let him continue to ride that frame in its current condition. When it fails and strands him several miles from home, remind him what you recommended and why he rejected the advice. The long walk home should give him plenty of time to ponder your sudden wisdom.
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Old 05-15-12, 05:15 PM   #20
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The welds look generous... like an aluminum frame. They'd be unusually big beads for steel. If aluminum, then really, you're lucky to have a crack. Often, the failure mode is catastrophic. Aluminum can suddenly fail and the whole cup might break out of the right side of the shell and cause the right side crank to touch the ground, and then that could cause a major crash. If he insists on keeping the bike, I'd find a steel ring that just fits over the BB and press fit that thing on and put epoxy on it to prevent slide off. It might only last a few more rides and fall off.
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