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I just picked this frame up for $100. Is this a crack? It looks and feels deeper than a surface scratch. I intended on this being my 1st build, should I continue? I hope I didn't waste my money Frame 1 Frame 2 Bianchi

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    The starting point is a concern - right on a small radius corner - exactly where a crack would start. I would suggest treat it as crack until proven otherwise.
    – mattnz
    Jul 29, 2017 at 21:20
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    Sand it down and find out
    – paparazzo
    Jul 29, 2017 at 23:08
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    You can tell steel from alu with magnets ;)
    – PTwr
    Jul 29, 2017 at 23:19
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    Apropos of nothing: what is that a braze on for? It looks like it's for a friction shifter but the bike looks too new for downtube shifting. It'd be a weird place and too big for cable guides.
    – RoboKaren
    Jul 30, 2017 at 2:35
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    Borrow an endoscope camera, there are cheap digital ones and route it inside from the steering tube. If it's a crack you'll see it from the inside as well!
    – Carel
    Jul 30, 2017 at 20:31

2 Answers 2

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Yes, that is a crack, or at least looks to be with about as much certainty as a pic can provide. That's a relatively common place for cracks to occur, with the thick square-edged boss creating a stress riser on the thin tube.

That the line of it continues into the area where a shifter or cable stop would cover the paint adds to my doubt that it's a scratch in the paint.

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  • Yes, you can see the surface level difference in the reflections.
    – edeverett
    Jul 30, 2017 at 7:37
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The only way to know for sure (unless you have access to an X-ray machine or ultrasonic tester from your side job ... say at Boeing or Airbus) is to take the paint off and see if it's a surface scratch or deep crack.

Since it's a metal bike, sanding it down won't hurt it and if it is a crack, your bike is toast anyway. Aluminum frames can't affordably rewelded like a steel frame.

Update: If you have balls or labia of steel and are willing to risk it (WARNING: STUPID ADVICE FOLLOWS) you could mark the endpoint of the crack with a sharpie and carefully monitor its progress while riding gently. If it lengthens or widens, it's a crack. If it doesn't, it still might be a crack. In any case, it'd be highly risky.

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