Hi Larry and Larry,
LR172 Larry, do you know of any definitive test data, analysis or publication by Lycoming that says lead on the valve face prevents wear? I have been unable to find anything in all my searching. In fact, everything I can find seems to indicate the opposite, and that any buildup on the valves is not a good thing, be it from lead or coking oil. The reason is twofold, first is that the small amount of rotation (approximately 1 revolution per minute) that the valve performs is designed to keep it concentric and ensure that the wear pattern is even throughout it's life so it fits neatly into the valve seat to best dissipate heat. Any buildup may prevent the even rotation. The second is that the thermal conductivity of lead is 44% less than that of the alloy steel that the valve seat is made of, essentially providing an insulation layer if there is any such buildup. According to the documents below, the leading killer of valves is excessive heat, so the more effectively the valve can dissipate the heat into the valve seat and subsequently into the highly conductive aluminum head, the better.
https://www.aopa.org/training-and-safety/air-safety-institute/valve-safety
There is a good publication that discusses this (although it is with regard to helicopters) and stresses the importance of having a good surface area between the valve and the valve seat to enable the heat to be pulled away from the valve and prevent distortion. Page 16 of the following article has some great info on this:
https://austhia.com/PDfs/AHIA-piston-engine-durability-report.pdf
Going back to a 1977 publication from Lycoming on valves, they stress the importance of keeping heat away from the valves. They make no mention of the benefits of lead:
https://www.lycoming.com/sites/default/files/SB301B.pdf
In fact in all the documentation I have ever read published by Lycoming, I have never found anything that has stated that lead has any benefit other than providing detonation resistance and the benefits of the low vapor pressure in fuel systems not designed to handle the higher RVP of mogas. Everything else I have found from Lycoming regarding lead is generally a mitigation measure trying to deal with the secondary problems is causes, such as lead bromide corrosion related problems, plug fouling, hub fouling, high oil change interval requirements, etc etc.
I'm not alone in this quest to find concrete data saying lead is necessary for anything other than detonation resistance in NA engines with CR greater than 8.5:1 and for fuel systems inadequately designed to handle the higher RVP of mogas, take it from John Deakin:
https://www.avweb.com/features/pelicans-perch-55lead-in-the-hogwash/
If you are able to find anything worthy of review, but all means send it in my direction.
Regards,
Tom Mills
RV-7, IO-360 M1B, 8.5:1 CR, 2xPMAGS, than only drinks mogas.