Spark plug blew out ? on 2001 Lincoln Town Car

threads in engine stripped had to put a "Hei core? and coil pack? changed out the other plugs also.what would the repair should have cost? I paid $525.00

Asked by for the 2001 Lincoln Town Car
This is the type of repair that is hard to estimate, it depends on how many plugs blew out, and what the condition of the other plugs and threads were in. At first glance the estimate sounds about right, but this is a good question for a Ford mechanic.
Ford has had quite a problem on some of their engines, although I haven't heard of it on the 4.6L V8 that you have in your Town Car. You can find quite a bit of info at this site:
Thank You, But what would cause a plug to blow out of the engine? I have put 50k miles on it with not trouble.
We did find out that the new plugs had a longer threaded shaft then what was in there. Could there have been a recall because of the shorter plugs?