Knock Sensor Threads Leaking

[BlindSquirrel]

1 hour ago, uk_exile said:

@Vach6 @justgary @butter71 I'm confused as there's mention of 1/2"-20UNF and 1/8"-18NPT and 1/8NPT and 1/4-18 NPT. I've grown up fully metric so imperial is like a foreign language! Surely these are all quite different? My knock sensor only screws in 3 or 4 turns and I've noticed the engine block threads look quite full of rust. What's the correct tap?   

 

I am 100% sure that 1/4 - 18 NPT is the correct tap and thread for the knock sensor. I did mine about a month ago.

Edited October 17, 2023 by BlindSquirrel

[Vach6]

Thanks guys. Sorry for the confusion on the size of the knock sensor. It's definitely a tapered 1/4"-18NPT. Regarding the block hole, I never tried an NPT tap, I've always used the straight tap that I mentioned to clean the block female threads before reinstalling the knock sensor. Driving the tapered knock sensor into either a straight or tapered female hole will wedge up and seal. I'll attempt to get a clear answer from a GM contact what the block hole was tapped originally. You can't go wrong with what butter71 says though.

 

  

Thanks for letting me know that the GM knock sensor is a good replacement for my 5.7L. I'm going to replace my knock sensor. I am only getting 1 to maybe 2 turns on my current knock sensor.

[justgary]

10 hours ago, butter71 said:

Also I occasionally use a 1/4-18 NPT tap to clean up the threads in the block, as justgary suggests above.

I didn't suggest a tap in the block, I suggested that @Vach6 use a die to extend the male threads on his knock sensor.  The photo he showed looks like he has room for a few more threads, so why not give it a try (especially if you have the die lying around)?