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.

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.  

Thanks for all the tips guys.

I ALSO WANNA ADD THAT MY STARTER HAS BEEN SLUGGISH TO START THE BOAT LAST FEW TIMES OUT, SOMETIMES IT WOULD SPIN OVER QUICKLY AND SOMETIEMES IT WOULD BARELY START THE BOAT. 

37 minutes ago, bwski said:

While I'm not sure how it exactly works in the boating world, typically the dealer has to purchase the parts, even if warranty.  After the repair is made the dealer applies for warranty reimbursement, which would incude the parts and the labor.  If the bank owns their boat inventory, chances are they, or another bank owns the parts inventory.  The banks may not be interested in taking on any new inventory even if under warranty.  The only other option is operating capital, which there may not be much!

I'd say the situation probably merits them taking a track different from the norm in order to get retail customers taken care of.

According to my source.

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)