So I have a 1A stem and the inside of the clamp is completely smooth. No matter how tight I crank the bolt I can still turn the bar if I try hard enough and it's not hard enough to make me think it will be safe for riding. Has anyone else encountered this? The texturing on the cinelli bars is not very rough either to that doesn't help. I was thinking of either a shim of some sort or texturing the inside of the clamp, say with a knife or razon and putting lines in it.. any suggestions before I mess it up?

I used a dab of rubber cement on my Record seatpost from slipping inside my Cinelli track frame. It created just enough friction to hold it tight. This may work your on bar/ stem combo as well....I don't know.

The obvious first thing to check is that you have a 26.4 handlebar. If so you can probably get away with a shim. Or possibly using a center punch to "peen" some spots inside the stem clamp area to give it some tooth. But with that said, these pieces may just be worn out and ready for the trash bin. A bar and stem is no place to put economy in front of safety. NOS 1A's are still available and the black ano ones go pretty cheap. They are easily stripped and polish up beautifully. Something to consider.

I definately have a 26.4 bar, when did cinelli start offering 26.0? But anyway the bar is old enough that I am sure it is 26.4, I have a couple other cinelli bars I can try but I am pretty damn sure of this. The centerpunch thing is a good Idea, I think I'll try that. It seems kind of off that there is not texturing to the inside of the clamp.

I'd recommend just measuring the bar before you add blemishes to things. You (and we!) might be surprised.

My calipers are plastic and suck so measuring .4 of a mm is not withing the margin of error. Besides it's hard enough to get the bars in the clamp in the first place.

Another thing to check is that the clamp bolt is not bottoming out for some reason before the clamp is actually as tight as it could be. The nut may have dug in a bit and you are running out of threads?

also make sure the bolt is grased well, ive seen bolts that feel tight but not actually as tight as they could be because of the friction of not being lubed.

I dont think texture is what holds bars in place. Ive never had a seatpost with any kind of texture on it and dont have issues with slipping posts...

While that is a good point I think that the forces are different on a seatpost. I am going to try and find an extra washer to add a mm to the length of the bolt before it bottoms out to see if that will make a difference.

problem solved, I realised that texturing would scratch the bars when installed. Luckily I found another brass washer on a 3ttt stem that had broken which I could use. So I put it on and tried it out. It worked... after looking at it I believe the problem could very well have been that the nut part of the fixing bolt was hitting the opposite side of the gap and therefore limited the tightening. Perhaps if I remove everything again and examine it I will be able to see where it was hitting and file away a bit of aluminum to eliminate the problem but I might just leave it with the extra washer now that it back together.