Compression test fitting

[RedBear]

I’m trying to do a compression test on my 1997 Ranger 4.0L OHV engine and I cannot get the compression test fitting to thread into the block. Admittedly it is the cheap compression test kit from Harbor Freight, but I already owned it for testing my old Acura a decade ago. Do I need a special fitting to get it to thread in? I thought the thread was 14 mm but the 14 won’t catch and thread. I’ve taken out my wheel well liner to get a better angle and still no go.

Sorry if this has been asked and answered before. I couldn’t find it in the sea of compression test questions / answers when I searched

 

[Dirtman]

What part number is the plug listed in the owners manual? You can look up the thread by that. It's possible It's still an SAE thread.

 

[RedBear]

The owners manual says part “AGRF22P” as best I can find on good old google, that’s a 14mm x 1.25 plug (tapered). I had replaced all 6 earlier with 14 mm Denso PT16TT and all but cylinder 1 are running well. It could be the plug but I want to test the compression.

 

[SenorNoob]

I ended up buying a "spark plug non-fouler" to get enough reach on my harbor freight kit to make it work. Still kinda a PITA to remove and reinstall both pieces every time.