Originally Posted by
rccardr
The wedge face has a series of grooves cut into it; the bar clamping area also has a series of grooves. These grooves should work together to keep the bar from rotating. If the 'teeth' on the grooves are worn smooth, the clamping action will be weak.
Sometimes, things just wear out; that may be the case here.
Actually just found out that there is no grooves in the handlebar. It is a Cinelli hexagonal handlebar, but as opposed to this model :
https://www.ebay.com/itm/NOS-CINELLI...-/303481702199 ; mine has no groove. See below.
Here is a photo of the back to the wedge "ramp". I don't know if the flat top is natural but I don't see this being the cause of my problem.
Here is the wedge which is pulled down by the bolt. Looks in good shape. There also was a small metal plate between the two pieces as you can see.
The only issue I can detect is with the shape of the handlebar. It seem to match the ramp quite well when you put the bar in a lower position, as below (sorry for the dirty hands):
But the ramp does not perfectly match the surface when you put them in a higher position. There's a small gab I can't get rid off. I imagine the bar isn't perfetly circular, although it's tough to detect just by looking at it.
Even though this is not highly scientific, I tried to match the wedge with another cinelli bar, just by hand, without actually installing them in the stem, and the problem does not seem to occur.
It is possible that the bar lost its original shape due to excess pressure? Would that mean that the bar is
kaputt, for such a small detail? Wouldn't it stil be safe to ride it in a lower position?