Originally Posted by
rutan around
A.E.F.R says:
Really? If the lead salt deposit you're talking about is lead oxybromide how does it deposit on those mating surfaces? Lead oxybromide melts at 703.4*F. The engine exhaust is between 750*F and 1,650*F so it is in liquid form. The exhaust gas exits through the open valve at better than 600 km/h The valve head is heated to close to the exhaust gas temperature. Under those conditions I don't think anything would stick to to mating surfaces.
The most convincing argument for me that it is an old wives tale that lead is a lubricant and /or cushion is the result when natural gas or propane gas is used in internal combustion engines instead of leaded fuel. The engines last just as long if not longer and there is not an atom of lead in either gas.
It's pretty well documented that there were a lot of problems with rapid valve seat recession when lead was removed from gasoline. You're may right that "lubrication" may not be the best word for what the lead was doing
something . How would you describe what the lead was doing to prevent that? Because I think you're going to have a pretty tough battle convincing anyone that valve seat recession wasn't a problem when automobiles were switching to unleaded fuel.