Fred, let me add a little tid-bit.  While I was at GM (yes the Feds and UAW own them now) we ran a little test.  We asked 20 “car type” people to install spark plugs in an engine without a torque wrench.  As I remember over half of the spark plugs were torqued above specification.  Of those plugs torqued above spec, many had cracked ceramic insulators.  Sorry I can’t remember the exact numbers but it stuck with me and I always use a torque wrench to install spark plugs.  Personally if I take plugs out of an engine, I generally replace them.  The break-a-way torque required to remove them is usually pretty high.

Craig Berland

 

“The problem was a broken piece of ceramic in one spark plug, too large to fall out.”

 

Glowing ceramic leads to pre-ignition or detonation leads to rapid CHT rise.  Makes sense to me. 

 

Now THAT is a valuable observation we should all tuck away into memory banks.  Very observant, Bill.

 

Fred Moreno