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I am buying a second-hand road bike. This is one of the candidates. It looks like a nice bike, except for this crack on the head tube.

I have read that bikes with cracks on their frame should not be ridden for a single meter because they could fail anytime. Is this the same diagnosis for a crack of this size?

Thanks a lot.

enter image description here

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    Can you confirm the frame material to save us guessing? That might indicate whether it's repairable and whether there's a possibility of it being just a scratch. I certainly wouldn't set out on a bike with a suspected head tube crack, let alone buy one. I'd also worry about the state of the fork given how that area is likely to be damaged
    – Chris H
    Aug 25, 2022 at 11:51
  • If the frame's aluminum I certainly wouldn't buy it. Dunno about carbon, and it's unlikely to be steel. Aug 25, 2022 at 12:55
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    That frame is toast.
    – Paul H
    Aug 25, 2022 at 15:32
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    @PaulH That could just be a crack in the paint, but there's no real easy way to tell. A tap test is probably worth trying. But a tap test can only tell you that the frame is cracked - it can't tell you that it isn't. Aug 26, 2022 at 19:37
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    That looks like it may have been caused when a new headset was installed misaligned causing the headtube to crack. I saw a mechanic force my headset cups in completely wonky and that was using the proper parktool headset press. He didn't seem to care and when I pointed it out, just said it'll be fine. Also I know of a shop that uses a vice and blocks of wood to push headsets in 🤦‍♂️. Don't assume your local bike shop mechanic can actually do the job properly.
    – Neil
    May 24, 2023 at 17:11

1 Answer 1

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That spot on the headset is not normally loaded during steady-state riding, because the weight is normally on the opposite side of that bearing.

Option 1 The prime suspect for this is a frontal impact - the bike was ridden into an immovable object like a car or kerb/curb or pothole, and the front wheel was pushed back. The top of the fork was levered forward, stressing the head tube which cracked.

Option 2 The headset bearing was forced into an undersized hole with pressure. Over time the stressed headtube cracked, but this happened after painting.

Option 3 The paint has cracked due to... something ?

I would say the seller is being potentially dishonest not disclosing details they know, or they may literally not know of this problem. On balance, I'd buy a different bike or use this one as a parts-donor only.

Checking If you already owned this bike, your best action is to completely disassemble the headset and remove the fork and upper bearing race. This lets you see the affected area from the other side.

If the crack propagates through to the inside, the frame is not safe to ride. Aluminium would be a write-off, but a carbon fibre specialist may have skills to repair it. In that case, consult a frame specialist in your area in person.

If you still can't tell, use a sharp pick or point to remove paint (no sanding or filing) to see the surface underneath. If it is just a crack in the paint then sand it smooth and apply a suitable colour of touchup paint, either automotive or nail polish. You may need 3-6 very thin coats allowinfg dry time, and then some clearcoat on top.

Risk If the crack was all the way through, it becomes a focus for stresses and may continue to spread. A frontal impact (like a pothole) while riding could result in excessive damage and immediate failure larger than what you might expect from an undamaged bike.

Gradual crack propagation might be missed too - the bike suddenly gets really floppy and you stop before it fails outright.

Summary You buy an undamaged and safer bike. Share this with the owner so they can act ethically (part it out and scrap frame, if they were OP then they check warranty, etc.) There's always another bike.

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