In a previous column, CYA, the FAA and the new unleaded avgas, I discussed the problems the FAA may have with the new proposed unleaded 100 octane avgas.
In addition to the lower octane characteristics of the avgas, one of the big concerns is exhaust valve recession.
I received a number of responses to the column, both positive and negative. The best email was from Larry Wheelock, who commented about the example of possible valve recession in Franklin engines.
He noted that the low performance Franklin engines were qualified on unleaded gasoline and, because of their low operating temperatures, actually had problems running on higher lead content fuels. The valve face temperatures ran at a temperature too low to scuff off the lead byproducts of combustion.
I apologize to Franklin owners; I should have been more specific as to which models could be affected.
This brings up the question as to which engines may be affected by valve recession with the unleaded fuel. [Read more…]