I was changing my plugs yesterday in my 1993 fd. Eveything was going fine when I get to the final plug. Got it out o.k. but when I tried to put the new one in it would screw in about halfway down the threads on the plug and then just jam up. This thing will not go in. I don't want to crank down on it too hard in fear of crossthreading. Has anyone ever had this problem Usually when I have cross threaded something it starts near the top of the threads.. not half way down. Anyway I am going to try to run a tap through it. I think what I need is 14mm. Is this correct? 20 minutes to change 3 plugs and now almost a day in a half on the fourth!!! It is driving me crazy!!!

 

Try swapping it with the other plug that went in fine, maybe the plug threading is messed up on that specific plug you are having trouble with. Any other problem is user error if the original plug came out fine.

 

already tried to put the other plug back in. No deal, it binds up in exactly the same place. I would agree with you in most cases on the user error but I haven't really cranked down on this thing... I can hand tighten it down about halfway. That is about 5 threads down on the plug....