Actually, the myth was that the lead oxide produced an "ablative
coating" -- that is, one that wears away but doesn't wear the
underlying seat -- and protected the valve seats in cheapo crap
Detroit motors with the valve seat (and guide) machined directly into
the cast iron of the head. This is bunkum -- the lead oxide acts as
a grinding compound on the valve seats, not a "lubricant" or
"ablative coating" or any such nonsense, to say nothing of the lead
oxide powder that got into the oil and goes through the filter. All
you have to do is look a the seat when you take the valve out and see
the nice, shiny ring on both valve and seat, unless there was so much
crap on it that the valve didn't seat at all, which wasn't uncommon.
Nor was a wad of melted lead oxide on the spark plug!
Remember "lead fouling" where the deposits melted at high speed and
load and shorted the plugs out?
After all the screaming and bullshit, it turned out that not only was
there no damage from using unleaded fuel in such engines, they
typically lasted 100,000 miles longer when unleaded fuel was used.
GM didn't stop using directly machined valve seats and guides until
they started using aluminum heads, and the buggers go forever.
Don't forget, leaded premium had up to 4 grams of lead per gallon in
it -- you could get lead poisoning by pumping gas!
Peter
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