I have a 07 TL-S, got a bad head on the front of the motor, shot a coil pack and plug out of cylinder. Retapped, and then happened again. So now I can't repair it is gotta replace the head. I cannot find a stock front head but I can find a rear. Now I think it's a stupid question but does anyone know if they're interchangeable? I'm seeming not but hoping so. Also any ideas as to why it keeps happening? Aside from a stretched timing chain which is being replaced.

 

probabky happened from being loose in first place and when you retapped you didn't have enough aluminum for the new thread to hold the plug tightly.

and these cars use belts not chains, I don't think belt or chain can cause plug to come out loose.