2200 Monster front bearing problem

I bought a used Eight T with a Losi electric conversion installed. I installed a "new" Monster 2200kv system and have been having issues with the front bearing on the motor blowing out. I am geared mild at 12/47 on 4s with the punch control turned down 10 and the end point reduced by 30. I have drilled and tapped the motor endbell for 4mm screws and they do not loosen until I loosen them. When the bearing goes out, the pinion normally is destoyed. Gear mesh is set perfect each time.
Does anyone have any help with this problem?
Thanks in advance,
Brian