I thought my spark plug problems were behind me when I changed them on my F150. I did the plugs on my wife's '07 Explorer today and now have one that won't tighten up. I put them all in my hand, so no chance of a cross thread, but after it's as tight as I could get it with my fingers, I put a wrench on it and it gets a little tighter, but never bottoms out. I just stopped there and started it up and it's running great, but I'm afraid it's going to spit the plug back out. Any ideas on what to do? I'm planning to call around tomorrow to see if I can have it heli-coiled with the head still on the engine. I'm pretty sure this is possible, but you guys have any other ideas? I'm tempted to try and tighten it up more, but am afraid I'll only be stripping it out more. sigh!

 

Try cleaning the threads in the spark plug hole with a chaser.

You can get one from an auto parts store or do as I did: take your old spark plug and cut 2-3 vertical grooves across the thread with a grinder wheel. Now you have a chaser that fits your plug hole perfectly. Put a dab or two of oil on your chaser to pick-up dirt and any (hopefully not) metal shavings.

Work your chaser in and out once, being careful not to cross-thread. Then wipe the hole dry with a rag and try threading the new plug.