Actually, it turned out that removing lead from gasoline REDUCED valve
wear -- lead oxide is an abrasive, and far from collecting and making a
wear resistant surface, it was actively grinding on the valves and seat
as the valve operated.
Fine lead oxide particles made their way into the oil as well, nicely
"polishing" the oil carrying hone marks off the cylinder walls and
slowly reducing the size of crankshaft journals and wrist pins.
Engines last much longer without the lead than with it.
Not the same with sulfur containing compounds in diesel fuel, though --
they provide most of the lubrication qualities. I believer there are
now additives in the fuel to restore it's lubricating properties.
Peter
