I had a spark plug do sumthing similar one time. I ran it in 4 or 5 turns by hand then it got a little hard so i put the wrench on it. I turned it another turn or so and it kept getting harder. I said sumthing ain't right! When I tried to back it out, it turned just a little and got REALLY hard to turn. I put a little muscle into it and got it out. I inspected the threads and there was a defect. It looked like a little barb, kinda like a fish hook. It only mangled about 2 threads in the head, so there was plenty of meat left for the plug to thread into.
Ever since then, I quite trusting company's to do what their supposed to... lol and try to inspect things more to find sumthing before it causes any damage.
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