Lead isn't added to help increase the lifetime of anything. In-fact, that's hilarious, because lead fouls spark plugs and the rest of the engine. I've personally removed spark plugs with pea sized nuggets of lead wedged in the electrode. Problems caused by lead (e.g., stuck valves) are probably the #1 reason you have to overhaul cylinders. Lead is an octane booster, that's it.
"Knocking" is an antiquated term. Knocking = detonation, and any severe detonation would destroy an aircraft engine. For example, this is why we take off with our mixture so rich, to create a huge margin against detonation by lowering internal cylinder pressures.
"Knocking" is an antiquated term. Knocking = detonation, and any severe detonation would destroy an aircraft engine. For example, this is why we take off with our mixture so rich, to create a huge margin against detonation by lowering internal cylinder pressures.
https://www.lycoming.com/node/17607