When I was changing the spark plugs in my 1991 Mazda 323 I messed up the threads on one and now it will only go three turns. I thought about what to do because the car is too old to spend the money to have the hole rebored and I wondered if I could get a spark plug with longer threads that would go in the proper depth. I looked up long reach spark plugs on the web but can’t find an equivalent for my car’s plugs. What would happen if I used a golf cart plug, NGK BP4ES to replace it, or something else that someone more knowlegable could suggest, as long as it has a long reach? Could it really hurt my engine? Of could it be a solution? Right now it runs okay, a little rough, but still gets 43MPH. It has almost 200,000 miles but just keeps trucking on.
Are you saying the threads on the plug actually stripped out or cross threaded the ones on the motor? That’d be a new one on me. Usually the plugs are softer steel…then again you probably have aluminum in the Mazda.
Did you try a thread cutter…looks like a drill bit but with gaps between the thread to cut new ones. Not too expensive and relatively easy to do. Like I said though, I’ve never actually had to recut threads for plugs, but I don’t see how/why this wouldn’t work.
I’ll check w/ my bro. in the AM. He’s a top notch mechanic and will know for sure.
See ya later & good luck. 
I was going to say, you can run it as is probably (with a miss) or just plug the hole for now. But don’t put one that’s too long or burns too hot unless you want to burn a hole in top of the piston.
Don’t run it as it is, if it’s not sealing right that cylinder will start to run lean and over heat and start to burn the piston. I wouldn’t tap the head with-out removing it because there will be metal filings falling in the cylinder.
I think h/b is right on both counts here. It was pretty late last night…I thought about the “not sealing right” and assumed that suezeekay would recognize whether the plug was at least tight enough to get by for right now…short term.
Also, you could just pull that plug wire until you fix it, one way or another.
and the metal filings, now that could be a problem. They could (probably would) be trapped on top the rings and scar the piston walls.
Then again we’re only talkig about repairing or straightening out a few crossed thread. Yeah, I know, it doesn’t take much. 
Perhaps pulling the heads isn’t too much touble, but I doubt it.
Brother was out of town. Sorry, I’ll check later.
Let me second t-keela’s advice. Get a spark plug tap. The local parts shop will sell you one for $5-8.
Legend has it that you can spray shaving cream into the spark plug hole to catch any metal shavings, then suck out the shaving cream. I’ve never tried this. Of all the beaters I’ve driven, none have been so bad off that I would be comfortable pumping them full of Gilette Foamy.
(I’m also at a loss for how you would suck out the shaving cream. Using an electric vacuum seems like a bad idea.)
And here’s a cite with more information on shaving cream and engines.