Burning the tips off is not "normal" and that plug looks like you have a lot of fouling happening as well. Do all 8 plugs look like that?

 

Looks like Ford swung and missed completely trying to update the older 2 piece plug. the ones that failed you are SP-547 and supposed to be "upgraded". Did you still use the nickel anti-seize on the snouts per the TSB? the ground straps are welded on instead of being made by grinding out material to make them. looks like the straps were to weak and burned thru then upon removal, stuck in the head and were pulled out. ill be sticking with the old 2 piece SP-514 plugs. that sucks bro, good luck

 

Agreed, blowing the tips off like that is NOT normal. What is normal for motorcraft plugs is the entire smooth piece below the thread breaking off from carbon build up, basically gluing that piece to the head. Just the tip like that is probably detonation. Better fix your A/F or timing issue before you burn a hole through a pistion.

if you haven’t already replaced the plugs , I would highly recommend using the Champion plugs 7989. Work awesome and they are a true one-piece plug so they will never break apart like the motorcraft plugs.

Motorcraft sp547 is a revised plug but it’s still a two piece. Instead of just crimping the two halves together like the older plugs, they also added a a couple of tack welds. Stronger but, can still break.

But to clarify, your problem isn’t really the plugs in this case. You’ve got,something going on with your timing/fuel. Do you have an aftermarket intake? What brand? Is it one of those “tunes not needed” ones? Often times those are a gamble.