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See picture below, I am in this situation with a new alluminium frame (don't ask me how I ended up here, it's a heartbreaking story.) It’s a Cinelli Mash Parallax.

The headtube has a dent and I don't know exactly what caused it, but the frame has allegedly never been used. With a bit of a stronger push than usual, my lbs mechanic managed to fit the headset. As for now, the bearings don't seem to be compressed by the dent, but I am still worried. I am going to ride this bike on the track, so I want it to be very reliable.

How safe is it? Do you suggest I try to fix the dent or will I only make it worse?

picture of headtube

More photos here: https://imgur.com/a/JdZKwU1

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    What material is the frame? Steel? Aluminum? Titanium? Carbon? – cmaster Dec 21 '18 at 13:39
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    edited the question with material and exact model – Alessandro Cosentino Dec 21 '18 at 17:56
  • I'm guessing the mech who installed the headset had a super-close look at the inside of the tube before? If there was cracking then they wouldn't have installed the bearing race? Did the mechanic say anything else ? – Criggie Dec 21 '18 at 21:07
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    @Criggie correct, mech said no cracking, he was only concerned about the possibility of bearings compression. – Alessandro Cosentino Dec 21 '18 at 21:27
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The dent is not in a high stress area.

If the headset turns OK, I would ride it.

Inspect regularly for cracks, both near the crack as well as the welded side of the headset.

  • I'm not sure I'd say the location of a major bearing is a 'low stress area'. During normal riding any bumps to the fork are transmitted right into that area on the front of the headtube – Argenti Apparatus Dec 21 '18 at 20:23
  • @ArgentiApparatus if it were at the bottom of the head tube, that's where all the weight is carried by the bearing. The top bearing is more for alignment and it also carries the weight of the fork and front wheel when the tyre is off the ground. So it is a low(er) stress location. – Criggie Dec 21 '18 at 21:04
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    @Criggie true, but when the wheel is forces backwards, the top of the steerer imparts a force on that forward section of the head tube. – Argenti Apparatus Dec 21 '18 at 21:09
  • @jefferybell in addition to inspecting, I'd suggest OP takes a photo every couple months to compare and make sure its not slowly deteriorating. I have a crack in something and because I see it every day, slow growth goes unnoticed. But comparing back to a year-old photo I could see the slow progression. – Criggie Dec 21 '18 at 21:09
  • @ArgentiApparatus excellent point - braking forces will push the inside of the dent somewhat, and given its already deformed one way will be easier to dent the other way, being aluminium. – Criggie Dec 21 '18 at 21:10
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It's hard to say for sure, but I think it's more probable than not that this will cause issues with headset adjustment, creaking noises, and/or bearing life. I've met bikes with welding distortion issues in the bearing seat area where the headset basically didn't work right, and I don't see why this wouldn't create a similar situation.

I would probably try just riding it as it is and seeing if there are problems before trying to fix it, because all the fixes are a little risky. If it came to it, I can imagine very carefully working the bulk of the dent out with an adjustable wrench or other jawed tool and then finishing with a integrated headset reaming tool to get the bearing seat good again. If you just reamed without doing anything else, my fear would be it's dented enough you might get the wall section down too thin that way.

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