Originally posted by kuafos:
be very careful. i had gone to three different parts stores. including pep boys auto zone. they all try to give you a spark plug with long threads. the stock plug is short thread. and the only place i have been able to find them is ford. and also. you don't have to take the coil pack off. i know some sites say you do. good luck
The threaded length does not matter (as long as it is long enough) - the taper seat is what sets the spark plug depth in the cylinder. Autolite/Motorcraft probably does not thread them all the way down (since they don't really need to) in order to save cycle time on that step of the manufacturing process.
See this
pic to demonstrate. See the taper that is almost directly below the "S" in the "Send eCard" link? That is what bottoms the plug, not how long the threads are. Both of those plugs have been in my engine and I didn't ram a piston into the NGK plug. As long as the length from the bottom of the taper to the end of the ground electrode is the same, you will be fine.
And, you don't HAVE to take the coil pack off, but the ~5 minutes that takes makes the job much easier.
