petrock

If your going to use a tap or anything similar, I would take the head off. You don’t want metal shavings from the tap getting into the cylinders. Good luck...

mbeer

Seems to me that there may be a coil in there that somehow got screwed down into the cylinder. That would explain why the plug goes in so far before the threads start.
If this is the case you would simply need to screw the coil out so the plug inserts properly.
Unfortunately I don't know how you would do that without taking the head off.

Maybe someone else would have an idea about that?

kilr95ss

mbeer, that's what a engine builder friend also said. When the spark plug was installed, they screwed the plug and insert down further in the head.

With this being my first GT and a 2V mod on top of that, pulling the head is going to be quite a job. Pulling the heads on my Impala was a breeze.

kilr95ss

Decided to pull the head, got with a local mustang "guru" and for him to do the work and replace my head with a used but in good shape one, he's charging me $750.

72MachOne99GT

I was going to comment on the other thread but I'll use this one.

I tried a timesert into my cylinder head. Something didn't go quite right. The car ran fine for a couple months before something happened while burning out some tires.

Had a bad miss. Pulled plug to find it mashed in. My best guess is the insert was threaded too deeply allowing the piston to make contact with the plug. I ended up replacing the head myself.

Either way, it would have been a good learning experience to replace the head, but I'm not one to judge somebody for wanting to get their stuff up and running quickly.