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="" />

You can tap the head.

Some tips to help keep shavings from falling in to a minimum:

Coat the tap with grease. Any aluminum they cut will
get trapped in the grease which will come out when you back the tap out.

Also, take a piece of cotton rope and soak it in motor oil.
Bring that cylinder up to just below TDC. Stuff the rope
down the plug hole in to the cylinder (be sure you have some springy fingers or some way to get it back out).
Fill the hole with the oil soaked rope as much as you can.
The oil on the cotton rope and the cotton rope will
help snatch any shavings that the grease didn't catch.
Pull the rope out gently and slow so you don't knock
any shavings off that it catches.

And after all is done and you get the rope back out,
take an air nozzle and blow out any residual debris that
may have stayed behind.

I will add that those threads could very well have been damaged by seizing. It's a good practice to lightly coat the plug threads in anti-seize lubricant to prevent this from recurring.

It should also be noted that you never want to remove spark plugs from aluminum heads when the engine is warm or hot. It should be done cold.

This is SO important, and I know a lot of people forget it.