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Re: Spark plug washers

PostPosted:Mon Feb 11, 2019 9:30 pm
by Trent772
Lycoming IO-360

NGK BR9EIX’s

Dual electronic ignition

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

Move on chaps, nothing to discuss here..... :wink:

Re: Spark plug washers

PostPosted:Mon Feb 11, 2019 9:54 pm
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)