How Does this Handlebar Bolt Work?
10-09-25 | 02:08 PM
#1
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How Does this Handlebar Bolt Work?
Hello. I'm trying to adjust the handlebars on this Carnielli stem, and I'm unable to loosen (or for that matter) tighten the stem bolt. There is nothing on the front of the bolt to react the torque applied to the nut, such that the bolt just spins around? Searching the threads I saw a Cinelli stem with a keyed or serrated bolt. Is that what is used in this stem? Or am I missing something obvious (I don't know why the bolt head has a flat on one side)? Thanks
10-09-25 | 02:12 PM
#2
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The flat on the side of the bolt is supposed to engage the flat on the stem casting to keep the bolt from spinning. It looks like you might have the wrong bolt or the flat on the stem has worn away.
Brent
Brent
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10-09-25 | 02:17 PM
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Interesting. Thanks obrentharris ! That seems logical, maybe I'll try to find something to jam in the gap to help.
10-09-25 | 02:22 PM
#4
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If you line up the two flat sections on the stem and bolt you might be able to wedge the gap with a large flat blade screwdriver or piece of flat metal (whatever fits the gap) to allow you to unscrew.
Alternately it looks like you could grab the bolt in the middle from the bottom with pliers or needle nose vicegrips. Since the bolt doesn't work/engage, it wouldn't matter much if you marred it getting it removed.
Alternately it looks like you could grab the bolt in the middle from the bottom with pliers or needle nose vicegrips. Since the bolt doesn't work/engage, it wouldn't matter much if you marred it getting it removed.
10-09-25 | 02:28 PM
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And then I would find another bolt to grind down to match the flat on the stem. 
10-09-25 | 06:45 PM
#6
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I would be careful with a cast aluminum stem like that. Is the part that goes in the frame straight ? It looks a little curved in one of the pictures, although that could just be distortion from the camera.
I agree with one of the prior answers, that is likely a replacement bolt. If you're lucky you have a Bike Co-Op near you to hopefully find a replacement. Sometimes a seatbolt can work. Grind a little flat and you'll be set.
Or simply shove a thick screwdriver in there while you turn the nut.
Good Luck !
I agree with one of the prior answers, that is likely a replacement bolt. If you're lucky you have a Bike Co-Op near you to hopefully find a replacement. Sometimes a seatbolt can work. Grind a little flat and you'll be set.
Or simply shove a thick screwdriver in there while you turn the nut.
Good Luck !
10-09-25 | 07:31 PM
#7
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Turn the bolt back a bit so that flat is parallel to the flat on the stem. Put an Allen wrench in between the 2 flats and it should hold to undo the nut.
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10-09-25 | 08:47 PM
#8
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Thanks for all the suggestions. I did try them all in the gap: a screwdriver, an allen wrench, a washer, vice-grips. Ultimately, the nut seemed like it was seized. So, seeing how it's not the right bolt anyway I finally pulled out the hack saw. I've got a regular hex head bolt in now for the time being, doesn't look quite correct but it'll do for the weekend bike trip!
