I worked as an Engine Machinist for a time, and I was told that lead in the fuel aided in sealing the valves, kept valves cooler by helping seal the valve, possibly acting as an impact damper, prevented valves from sticking to the seat and slowed corrosion. When lead was removed from fuel, common practice is to use a valve seat insert made from a different material, usually a high nickel alloy.
Lead fuel was during a time when the cylinder heads were mostly cast-iron, and the valve seat was cut directly into the head. Cast iron is an interesting material, it's reasonably durable, but it corrodes/rusts very easily, especially when exposed to moisture. Gasoline and ethanol both have water as combustion byproducts, so when the engine is off and cools, some of that moisture condenses inside the engine.
Running straight ethanol in an engine without corrosion resistant materials causes much more wear over time because it tends to strip the protective/lubricative oil barriers away, causing iron to corrode when the engine isn't running. Modern engines are aluminum heads with valve seat inserts, stainless steel valves, better piston ring materials (high chromium I think? these were cast iron in the past).
Ethanol has a significant detergent/cleaning effect, even when at 5-10% concentration in gasoline. The valve stems also get some of their lubrication from the fuel, and gasoline is basically a thin oil, and provides protection to mechanical components, better yet with additives. Ethanol is also a difficult fuel in a cold start situation and requires good compression and a strong ignition system to kick it off.
I suspect the whole reason to want to keep lead was motivated by the bean counters involved. They saw a cost savings with lead in the fuel. Cheaper materials and no tooling changes. This means more profits.
> Modern engines are aluminum heads with valve seat inserts, stainless steel valves, better piston ring materials (high chromium I think? these were cast iron in the past).
You say "modern", but that's a fairly typical 1980s car engine.
Lead fuel was during a time when the cylinder heads were mostly cast-iron, and the valve seat was cut directly into the head. Cast iron is an interesting material, it's reasonably durable, but it corrodes/rusts very easily, especially when exposed to moisture. Gasoline and ethanol both have water as combustion byproducts, so when the engine is off and cools, some of that moisture condenses inside the engine.
Running straight ethanol in an engine without corrosion resistant materials causes much more wear over time because it tends to strip the protective/lubricative oil barriers away, causing iron to corrode when the engine isn't running. Modern engines are aluminum heads with valve seat inserts, stainless steel valves, better piston ring materials (high chromium I think? these were cast iron in the past).
Ethanol has a significant detergent/cleaning effect, even when at 5-10% concentration in gasoline. The valve stems also get some of their lubrication from the fuel, and gasoline is basically a thin oil, and provides protection to mechanical components, better yet with additives. Ethanol is also a difficult fuel in a cold start situation and requires good compression and a strong ignition system to kick it off.
I suspect the whole reason to want to keep lead was motivated by the bean counters involved. They saw a cost savings with lead in the fuel. Cheaper materials and no tooling changes. This means more profits.