ORIGINAL: combatpigg

Get the problem nipped in the bud before you damage the engine.

bubbless tank OK
20% oil fuel with some castor
bearings with no axial play, good fitting rod, wrist pin, crank pin, no slop anywhere
head button with tight fit in liner
pipe too small?
raise liner
stack in more head shims
coldest plug
too much prop diameter, blade area, blade thickness
too much nitro for combustion chamber type and chosen head clearance
fuel delivery system isn't keeping up with demand because of pressure leaks, crappy carb
[run a venturi and fuel line pinch]
stiffest of the stiff engine mount
balanced prop

It's possible to get an engine to run in this range without getting hot, but the plugs can get buzzed out of shape if you combine certain factors or just find the single culprit.
Too much compression is a biggie, same with too small/short of an exhaust system.
Setting the needle so that the engine doesn't completely clean up until the tank is almost empty, then slowly get more aggressive in subsequent flights is a good way to go.
Expect to consume plug elements [turned to chalk] every few flights when you're running this hard.