My VIII was overdue for new plugs, 1-3 were changed out with no drama, but #4 was difficult to break loose. It took much more force to get turning than 1-3. Replacing #4 it seemed that it required more turns to get it in, and I didn't feel the resistance I was expecting. I usually turn it until it stops, and then give it just a little more force to make it snug. This one I never got to that point. I turned until I felt resistance and stopped.

I'm concerned that I didn't go far enough, but am afraid if I go further I'll strip it entirely. If the threads are messed up can it be re tapped? Thinking about having someone look at it. If it's not in entirely its close to, or close to oblivion if something's wrong?

I think the last time I had that plug out, the threading felt weird, but it did seat.

 

The only fix I know of is Helicoil.