Bad Spark Plug Threads

I have a 1988 Isuzu Trooper. A few days ago it started running ruff. It felt as if the motor was only running on 3 cylinders. And in a matter of minutes the fourth spark plug came to life, evening out the ruff motor and restoring the power. My next move was to install some new plugs. Cylinder one, two and four all came out as expected, but number three was a really hard to remove.

At first I thought I was turning the wrench the wrong way. I thought that I was stripping the threads right out of my head, I felt ill. When the plug came out I was relieved to see no aluminum threads in the spark plug threads. What I did see was a kind of crushed thread one row up from the begining of the spark plug head. I still have not figured out what caused this to happen. If the plug was like this from the factory there would be no way that I could have installed it.

Anyway, when I put the fresh spark plug into hole number 3, I had a hard time too. I guess that the damaged spark plug fowled up my threads.

Is there any way that I can clean my threads or fix the threads without taking the head off? I'd like to clean the threads but only have taps and I am affraid of using that on my head.

Cheers <img src="/forums/images/graemlins/cheers.gif" alt="" />