[stkmtr]

I just finished plugging my oil pump for full flow. It is a cast iron melling and I used a 1/2 NPT plug. I know these are tapered to prevent leaking. I am also aware that if overe tightened they can crack parts. I tightened the plug firmly and reassembled the pump to find that it will not spin freely any more. Doses cast iron warp easily. Should I try to machine it and if so what should I use to do so-We have a bridge port mill ans a lathe-I feel that tossing a 50$ pump is a waste and how can I prevent this from happening again?-ss