These problems are often traced back to worn trunnion liners, which allow one slurry to "race" behind the liners. The continuous flow of abrasive slurry can erode the trunnion "fit" areas. Once the fit has worn away, there's no seal to keep slurry from the mill out of the space between the trunnion liner and the trunnion journal. Eventually, this will cause bearing failures or, possibly cause the mill head to split and crash to the floor.

Loss of the fit area means movement of the trunnion liner, which causes bolts to shear off.