This Thread linked from TV should cover everything necessary to extract the Spark Plug Remainder stuck inside of the Engine Head.
CAUTION:
Please ensure that as you shatter and gradually remove the Broken Pieces of the White Porcelain Ceramic Insulator (if any has been left inside of the HEX Body) ...to Vacuum out each and every last smidgen of that stuff, as it is MUCH harder than either the Cylinder, the Piston, the Rings or the Valves and will score, scratch and damage these components if these Ceramic Particles happen to drop down inside of the Cylinder during the final Plug Remnant Removal.
PLEASE WEAR EYE PROTECTION AND USE A HARDENED STEEL PIN PUNCH TO HAMMER UPON AND SHATTER THE REMAINING PORCELAIN JUNK.
If that Internal Steel Cavity is already cleaned out... using the proper sized EZ-Out ...lightly tapped down inside... and some very gradual counter-clockwise force... this should do the trick as only 18 Foot Pounds is ordinarily used (...but in this case, perhaps abused) to secure the Stock Spark Plugs.
Setting up everything in advance, (Cardboard or Pillows wrapped in Plastic Garbage Bags and preparing the Lighting) for helping with your Best Position and Comfort before attempting this repair will assist with being able to 'concentrate in comfort'... and not feel awkward or get anxious when using the Specialty Tools in such tight quarters.
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