John, you will find that it is the consensus of many of us here that have driven these old engines many miles that a lead substitute is unnecessary. Tetraethyl lead was initially used as an antiknock additive. It is claimed in some circles that a side effect was that it increased valve seat life but that seems to be purely subjective.
Here are a few articles that discuss the reasons that TEL was used in gasoline.
http://www.thenation.com/doc/20000320/kitman http://www.runet.edu/~wkovarik/ethylwar/
http://www.uwsp.edu/geo/courses/geog100/Lead-Science.htm This is an excerpt from an EAA paper from about ten years ago.
“Experience has shown greater extended life, and more time between overhauls, with the use of unleaded automobile gasoline. EAA had more than 500 hours of flight test time on each of the following aircraft when EAA's STC's were issued: Cessna 150 with a Continental engine, Cessna 182 with a Continental engine, Piper Cherokee PA-28-140 with a Lycoming engine, and a Cessna 172 with a Lycoming engine. A Cessna 172 in pipeline patrol satisfactorily flew a supervised 1,200 hours observed by the FAA. All aircraft performed very satisfactorily in actual flight tests for EAA and the FAA. Engine teardown inspection by an independent engine shop and witnessed by FAA representatives indicated no adverse wear problems with the use of unleaded automobile gasoline.”
Denny Graham
Sandwich, IL
