The place for technical discussions about GA and flying.
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By Trent772
Lycoming IO-360


Dual electronic ignition

$8 a plug, just fit new ones at the annual.

Move on chaps, nothing to discuss here..... :wink:
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By Rob L
My understanding (and I'm willing to be corrected) is that pure copper age-hardens with increased temperature. As we all know, the spark plug is the hottest part of the cylinder, so some of this heat is imparted to the copper washer. So it becomes hard with use.

Annealing it makes it soft again, which, when torquing it down beneath a spark plug, makes for a fresh seal between the cylinder and the spark plug face.

To offer an opinion (unfounded) about the Cylinder Head Temperature (CHT) gauge gaskets commonly found under spark plugs is that they are not pure copper (they are made of a bi-metallic alloy that detects temperature change)