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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 06-25-06, 12:35 PM   #1
Mchaz
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Cracked BB Shell

Hello everybody. Here's the story, I just bought a 1996ish Specialized Rockhopper A1 Comp (aluminum frame) from a guy for $40 to make a commuter out of. The components were a bit rough, but the bike had potential. After the half and hour drive, when I got home I flipped the bike over, and noticed a hairline crack running across the width of the bottom bracket shell. It is a little to one side of the drain/screw hole for the cable guides.

So my question is, is this safe to ride? It will be a commuter so the most it will see is a drop off a curb, or going through a pothole. It doesn't seem to pose a threat structurally because of the triangulation of the frame. I mean the whole frame couldn't suddenly split in half because of the top tube/seat stays holding it together. I thought about just putting some JB Weld epoxy in the crack and calling it good enough. I don't know though, and that's why I'm asking.

I'll post pics later, camera has to charge, grr.
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Old 06-25-06, 12:47 PM   #2
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Call the guy up and tell him you want your money back. The frame is trash. The BB shell takes a lot of stress (why the crack appeared in the first place) and will get worse with time.

JB Weld is of no use here and will do nothing to fix the problem.
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Old 06-25-06, 01:01 PM   #3
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The crack goes all the way across? I would not ride it anymore. And JB Weld will do no more for the strength of the metal than a piece of electrical tape.

If there is a crack going all the way across the BB shell, it is already flexing when you ride it. There's a lot of stress in that part of the frame. Aluminum doesn't like to flex and it's a sure bet there will be more cracking soon - if there isn't already. If it cracks across the top of the BB shell now, it very well could split open and spit out the crank, causing you much pain.
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Old 06-25-06, 02:43 PM   #4
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Thanks for the info guys, I call the guy up. I might just try to have him give me some money back because the wheels, crank, brakes, ect are still good.
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Old 06-25-06, 05:25 PM   #5
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What you have here is a dead bike, not just a cracked BB. bk
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Old 06-25-06, 11:04 PM   #6
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Yeah you should get your money back.

But I do know people who've had good luck with TIG welding aluminum. If you know someone who does TIG welding you could give that a shot.
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Old 06-25-06, 11:08 PM   #7
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Yeah you should get your money back.

But I do know people who've had good luck with TIG welding aluminum. If you know someone who does TIG welding you could give that a shot.
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Old 06-28-06, 10:13 PM   #8
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It's not just a matter of TIGing aluminum. Different aluminums respond differently to welding - that is, they retain different degrees of their pre-welded strength.

The most common aluminum alloys used in frame building fall into one of to categories: a) those that need artificial aging post-welding; b) those that need all out heat treatment post welding. The difference between the two processes seems to be primarily how hot, and how quickly cooled.

Anyway, these alloys require this additional step because welding takes a lot out of them.

Hence, I'm sure the crack can be TIGed, but I wouldn't ride the bike afterwords.
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Old 06-29-06, 06:26 AM   #9
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If you got some useful components your $40 wasn't badly spent and maybe you should only get part of the money back. Nashbar has brand new frames in both MTB, road and "touring" configuration, usually with a fork included, at very low prices and these would be a great start to a commuter or other utilitarian bike build.
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