I just installed a new wear-ring and there is a gap of 1mm (+) I'm not sure if its the wear-ring or the impeller. The impeller looks good but after i removed it, it appears as if it is warn on the leading edge of the impeller blades i think anyway. That being said it has an even gap from front to back of the impeller blade to wear-ring. The wear-ring is 7mm's on the wall thickness. My old wear-ring is also the same thickness. Not sure were the problem is either the wear-ring or the impeller. 
