PCM Excal knock sensor thread size

[peteSki]

I've got a 2005 Sport Nautique 216 with the Excalibur 330 engine 5.7L. I remove the knock sensor every fall to drain the block as part of the winterization of the engine. Last time I did it I noticed that the threads on the sensor have corroded away so I purchased a replacement sensor. This didn't go in the block very far as it seems the threads in the block are likely jammed up with pieces of the old sensor threads. I cleaned the threads out as best I can but want to do this correctly with a tap or thread cleaning tool. Hoping someone can confirm the exact thread size in the block so I can purchase the right tap. Anyone else who's faced this would of course like to hear your fix.

Pete

[MN Ryan]

Could you just take the sensor to a hardware store? They typically have gauges for determining thread size/pitch.

[mpost]

Searching for the R020027 part number one of the suppliers mentioned the following. It specified 1/4' NPT. that is what most of the older knock sensors are.
:

Knock Sensor for Crusader 48008 Pleasurecraft R020027 Indmar 556015 Quicksilver
1/4 inch NPT thread size
Single wire plug-in
Engine sensor sends a signal to the ECM when abnormal ignition occurs.

Applications:
Fit for follwing models:
GM Small Block marine engines like Mercruiser, OMC, Volvo, PCM, Marine Power and Crusader.
GM 305 5.0, 350 5.7, 377 6.2, small block V8 engines

[peteSki]

Thanks to you both. Should be able to get this sorted before the ice is out!

[jpwhit]

There's not much depth in the block behind that sensor hole. So you need a tap with a stub nose and not a lot of extra length. It can be hard to find one that'll work for this particular application and sometimes the easiest solution is to grind the tap to reduce the length. Just in case you're not familiar with NPT tapes, they are tapered taps.