Originally posted by psfred
....The idiocy about lead being "good" for engine parts is hogwash too -- this was propaganda bandied about by the American automobile companies to avoid putting inserted valve seats in cast iron heads, nothing more. The theory was that a layer of lead oxide on the valve and valve seat would "wear itself" as a permanent self-ablative coating rather than the valve or seat.
That turned out to be wistful thinking at best. Lead oxide, like all metal oxides, is considerably harder than any metal found in an automobile engine, and will grind away constantly....
A good post from Peter, but part of it doesn't make sense to me. If lead oxide is indeed abrasive, and the theory of lead oxide self-ablating the wear surfaces is indeed hogwash, then why are all engines now manufactured with hardened valve seats?