Is this being built from new? if so, sound defective, and could do with being returned, appears that the alloy in the face plate has been worn away by the harder steel from the handelbar. If you have tightened the bolt on the face plate of the stem to the max they will go by hand, you will most likely only shear them by using a regular torque (1/2 or 3/8 drive ) wrench unless you have a small one (1/4 drive).