Knock Sensor on 2000 Indmar Monsoon

[JL5]

I removed the knock sensor on my 2000 Indmar Monsoon when winterizing it last fall and noticed that the inserted end seemed to have been corroded and it was only held in place by a couple of threads. After adding antifreeze into the block, I left the old sensor in for the winter.  Fast forward to this spring and I have attempted to install a new one. Unfortunately I can only get it to thread in by a couple of threads which leads me to believe there is a lot of corrosion on the deeper block threads. I'm fairly certain that I have NOT cross threaded it.

Would you recommend chasing the threads to clean it, or is there any other methods or considerations that I should be aware of?  (It was running fine last season with the old corroded sensor)

[Nick55]

Should be 1/4 NPT so a thread chaser for that should work. But you should measure the sensor just to be sure.   Note: some older blocks had a 3/8 NPT and a small threaded fitting that the 1/4 NPT knock sensor threaded into.  My Supra had the 3/8 NPT.  

[butter71]

I occasionally use a 1/4-18 NPT tap to clean up the threads for the knock sensor in our 2000 LSV, also w/ an Indmar Monsoon.  There's still not a lot of thread engagement... it tightens up after just a few turns.  I don't think that's unusual due to the tapered nature of pipe threads, but seems like you should get more than 1-2 thread engagement.

[electricjohn]

I chase the threads about every 5 years and use a round 3/8" brass brush annually. I got my replacement knock sensor from Summit Racing. I do not tighten the plug or sensor much at all, perhaps hand tight, plus a 1/4 turn, then check for leaks. The water pressure down there never exceeds 7 PSI. I threaded a 0-15 PSI gauge (with max hold) into the drain plug to verify this. It's some of the silly things retired instrument techs do.

I also vacuum out the drain holes at seasons end to get any residual crud and water out of the block. Easily get an additional quart of water out and a bit of crud.

Edited May 8 by electricjohn

[JL5]

Thanks for the replies, I appreciate it.