I have Tempest spark plugs.
They were not new with the engine rebuild.
I put them into the engine after I first bought the plane.
I was trying to figure out why it ran rougher than I remember.
It was an estate sale.
The owner bought a new motorcycle the day before.
It was sold as 1350 since major overhaul.
But it wasn't.
It was a field overhaul, in 1981.
Then I realized the engine was a worn out piece of junk.
Sintered iron oil pump gears, AD'd in 1979.
Slick 4000 mags last overhauled in 1985.
They went in the dumpster and new Bendix's replaced them.
Engine, carburetor, magnetos, harness were all replaced/rebuilt.
I'm trying to get these plugs to 200 hours.
I have a new set ready on standby.
I'll try a LOP test when I go again.
But first some maintenance and upgrades.