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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92 300E - 116K miles - Sold
77 Euro 350SL - 67k miles
94 Explorer 147k miles
2009 Hyundai Genesis - 65k miles

This is my thouht: It should be possible to remove the insert and grind the difference off (2mm) to go flush with the inside of the spark plug hole. good luck Abe G

I thought of that, and so I "practiced" on one of the other inserts. I then tried to screw the insert into the newly tapped threads in the head and it didn't go in easily (the "unground" insert go in quite easily). I've made a couple of trips to hardware stores looking for a 16mm nut that I could "clean up" the threws on the ground insert, but couldn't find one.

After going through all this mess to fix the head, I sure don't want to mess up the threads I just tapped.

I'm not sure what I'm going to do, but whatever it is, I'm going to think about it for quite a while.

thanks

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92 300E - 116K miles - Sold
77 Euro 350SL - 67k miles
94 Explorer 147k miles
2009 Hyundai Genesis - 65k miles

This probably won't be too helpful but are you sure that you have the correct spark plugs?

Do you have a Dremel or tiny file that you could use to clean the edge of the threads up by hand?

The 16mm nut is the best way to go if you can do it.

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1987 300SDL 167k
1992 Volvo 740 140k
1990 Volvo 740 250k
1989 Volvo 240 269k

Anyone want to trade an old Volvo for an '87 300sdl?

Did you try a thread chaser first? I just recently had a cross-threaded sparkplug,,, Had to take 3 "breathers" to remove, it was either that tight,,, or I'm getting old.

Well anyway, I ran a thread chaser through the SP hole and the new spark plug took it great. I even have had to remove the spark plug and reinstall it,,, seems it's good to go,,, now onto the other problems of the car,,,

On a side note, what size did you have to drill the SP hole to get the insert tap started?

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Closing the store
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