Run the engine a short time, 10 - 20 minutes. The head expands a little faster than steel. When you get a plug a little loose, turn it tight again, back loose, sort of rocking it out. If it still won't get going, leave it between the full tight and stuck spot, and run in some of the WD-40 and come back later.

Just an idea - run engine until HOT, then try to get a cut-to-shape candle down into the seat area. It'll melt and capillary action will draw it farther into the threads.

A thread chaser will help, but can be dangerous if new threads are cut instead of clearing the existing ones.

Uns anti-sieze when installing plugs, torque to lower number.

Good Luck,

Bob

:>)