I'm having problems with the spark plug thread on my 2000 Expedition EB Left Hand cylinder head. I put a hiel coil in it, and it worked fine for about 3,000 miles, but now it is acting up again. I was told that if the vehicle was something that I was going to keep, to put a used head on it rather than try to fix the thread again, as they told me that I would continue to have problems with it. My question is, what year cylinder heads fit my vehicle. I called the ford garage, and they told me the 00-01 heads would only fit. Does anyone know if the machine shops are doing anything different to fix these ford heads. My head has already been tapped once, does this mean it can't be done again? If you buy a manf. head, they charge you a core charge for your head and then fix your old head and re-sell it.