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Yeah... um... so I was wrenching on my bike after it spent a month in the shed. I took the bike out. It was in BAD shape. Wow... so as I was cleaning it down and taking things apart to start repacking bearings, cleaning rust (god, that chain's nasty).. and I discovered this...




Now... it's an aluminum MTB frame that's _NEVER_ seen anything but on-road riding. (I know... shoulda bought a road bike). Now... it might be a scratch. It might be worse. I can't tell. I can't see light through the BB housing. But I can't clean the "blemish" either.

What're your thoughts?
 

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Don't think so

I don't reckon that's a crack. The underside of the bottom bracket shell is one place where I would least expect a crack on a frameset because even though your BB runs through that part of the frame it is an area of relatively little stress. It looks more like a deep scratch and nothing to worry too much about.
Also, if your down tube showed signs of cracking (in my experience most frames fail somewhere on the down tube, especially near the bottom bracket lug or weld) I would be a bit worried in the event of a failure – your bike could literally fall apart. A failure to the underside of your BB doesn't strike me as a particularly dangerous. What's the worst that could happen?
I would mark and measure the scratch and if it continues to grow – even a little bit – then it's a crack.
 

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simoriah said:
Yeah... um... so I was wrenching on my bike after it spent a month in the shed. I took the bike out. It was in BAD shape. Wow... so as I was cleaning it down and taking things apart to start repacking bearings, cleaning rust (god, that chain's nasty).. and I discovered this...




Now... it's an aluminum MTB frame that's _NEVER_ seen anything but on-road riding. (I know... shoulda bought a road bike). Now... it might be a scratch. It might be worse. I can't tell. I can't see light through the BB housing. But I can't clean the "blemish" either.

What're your thoughts?
Another vote to keep riding it. Hey, some road frames have the bottom bracket shells drilled out (for draining away water), and it doesn't really compromise the bike.

Is it possible that this is a casting mark, or a paint/plating imperfection? Try taking a pin or needle or scratch awl or whatever, and go exploring with that; much better than the nakked eye.
 
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