Spark Plug Theory 101

[keithb7]

I see that there are some real experts on engines here on this site. I have a question to post. Spark plug fouling. What exactly happens here? Breaking it down to basics, the plug electrode and insulator get coated in oil deposits and soot. So if I take it out and sandblast it like new, regap and reinstall it, why won't it perform as well or as long as a new plug? What is wearing out there? I understand heat ranges but this fowling is stumping me. A good sandblasting or glassbeading really, really gets the plug looking like new again. My son's 1976 Honda Z50A is really picky about fouled plugs. New plugs or, forget it, it won't start worth a darn. And it's a four stroke! But finiky, I tell ya, as bad as a 2 stroke.
Keith

 

[reelrazor]

Okay. The insulator is porcelain/ceramic. You bead or sandblast it and the surface becomes micropitted and holds more crap that is electrically conductive. Look at a new plug with a good magnifier and you will see it is almost a glossy finish, definately smooth. Then beadblast one and look at it with the same magnifier. It will look like a moonscape.

Think of an enamel/porcelain bathtub. When new, it is nice and shiny and any deposits can be wiped off, pretty much. After years of using comet, the finish gets dull and it takes no time at all for it to get dingy/dirty. And takes more work to get clean.

At least that's my theory.

 

[mtk]

Your theory is correct.