Toyota Repair: spark plugs, threading tool, penetrating oil

Question
Hey,
I recently bought a 89 4runner w/a 3.0L v6 5sp. I went to check the spark plugs and the first one I tried to remove loosened about 3/4 of a revolution then started to bind up. I re-tightened and tried another one. Same thing. Why won't they come out. Motor has 187k.
Thanks for any help.
Bob

Answer
Possibly the threads are stripped, this can be caused by carbon that has build up on the bottom of the threads, or just from the spark plugs being in there for a long time, this is not uncommon, try backing the plugs out a little and then spray some penetrating oil on the bottom and see if turning the plugs in/out will free them up, if the threads are damaged they can be repaired using a special threading tool and a steel insert, these are available at most autoparts stores in a repair kit, the thread size of the spark plugs is 14 mm x 1.25.