There is no need to remove the cylinder head, and no coil insert is required. You do not need to be concerned about debris entering the engine. High-Quality Material: Constructed from premium 42CrMo steel, which is equivalent to 4140 steel.
ABN 14mm Spark Plug Thread Repair Kit Rethreader Tool w/ Thread Inserts
14mm Spark Plug Thread Repair Tool Kit | M14x1.25 Tap & Chaser for Engine Thread
12x Helicoil 14mm Spark Plug Thread Repair Inserts #R513 14- 1.25mm Reach 7/16"
12x Helicoil 14mm Spark Plug Thread Repair Inserts #R512 14- 1.25mm 3/8" Reach
Powerbuilt 14mm Spark Plug Thread Repair Kit - 648421
14mm Spark Plug Thread Repair Tool - Back Tap, Straightening, Collapsible Design