Posted by Ken in CO on Thursday, October 26, 2000 at 14:51:21:
In Reply to: Funny thing about that... posted by Brian in Oregon on Wednesday, October 25, 2000 at 21:42:08:
In the late '80s I read a study done on exhaust valve and seat durability concerning lead/lack thereof. It involved tractor engines without hardened seats running unleaded, but is applicable to auto use. Various conditions were tested including: new seats/freshly cut under load and no load, used seats under load and no load.
The important part was that their findings led to the conclusion that an engine without hardened seats that had been run on leaded fuel for 500 hours would then have enough residual lead on the seats, and/or work hardening of the seat area which allowed them to survive another 1500 hours while being run on unleaded.
Just more factors to throw in the equation as to why some engines without hardened seats plod on while others quickly get leaky exhaust valves when run on unleaded.
My '58 Pontiac heads were fully rebuilt with new valves(had to have them made) and then run for about 5K miles on leaded. I've now been running them on unleaded for over 5 years and they still fully seal.