Originally Posted by
stanamas
This is the shot from another angle, so it is clear that the bar is not too big
+1 Ed, Dan, Scrub. Overtightened.
Look how close the faceplate is to the stem body. What is the gap I'm used to seeing there with (Thomson) stems, 2-3mm average? It's not there, in the OP's photo. Waaay tight.
I am assuming that the bar is the correct size, so the only way to close that gap is to overtighten the faceplate.
Faceplate's had its back broken over the clamping area of the bar.