I am still trying to put together an engine that I bought over a year ago and my latest problem has to do with sensor holes that are now stripped out. When I received the block their was a plug in the hole for the oil pressure switch above the oil filter, and one in the cylinder head where i needed to put the coolant temp sensor. I now have two drilled out plugs and pretty much no hope of getting them out without destroying the threads. Can someone tell me what the threads are for those two sensors or even better if someone has had to repair them on their engine, which helicoil kit you bought? I did a search but I didn't really find a definite answer and I wanted to make sure before i screw something up beyond repair. Thanks.

 

Coolant temp sensor in head should be 3/8 NPT. I'm not sure if a heli-coil exists in NPT thread sizes...? You might be able to drill it out and tap it for 1/2" NPT, and use a different sensor.

Not sure about the other one.

 

so why did you drill the plugs out? were they seized? the oil plug above the oil filter is 1/4npt the coolant one is 3/8npt. never seen helicoils for pipe threads cause they are tapered.