I had to "Rethread" a spark plug hole today, and I have a question for anyone who has done this before.

A little background 1st: I used a tool I purchased from NAPA - KD 2125 which reams and taps. The next step is to place one of the threaded replacement inserts onto the plug and screw the insert into the new hole. So far so good. The kit comes with 4 sized of inserts, and the only that is close to the proper length is the 3/4" insert. When the plug is fully seated in the insert the insert extends about 2 millimeters beyond the ends of the threads on the plug. It extends to about the same height as the ceramic insulator around the electrode.

My question is this - Is the OK for the insert to extend beyond the end of the threads on the plug? I've asked a couple of mechanics and they indicated it should be OK, but I was wondering why it would be made this way - To insure there is no carbon buildup between the insert and the plug that would prevent the plug from being taken out?

Hopefully, someone out there has used this product and has some helpful insight.

thanks

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