Posted by Old Timer on Sunday, December 17, 2000 at 14:54:13:
In Reply to: Valve Guides/valve seats/overhaul/leadedgas posted by John J Conrardy, D.C. on Sunday, December 17, 2000 at 09:52:23:
I drove MOPAR flat head in-line 6 and 8 cylinder engines in the 1950's on "white" gasoline routinely sold as motor fuel by several major oil companies. Now it's called "unleaded" and you young guys think it is something new. The use of "white" gasoline was common and it was okay to use it in cars and trucks built back then.
When the "muscle cars" came along with their high compression V-8's, their engines needed high-octane gas to prevent pre-detonation and a fuel additive to "lubricate" the valves and valve seats. Lead additive was already out there so leaded high test became the gasoline of choice.
The EPA said "no" to lead and the auto industry changed the metallurgy of valves and valve seats and oil companies changed the additives that "lubricate" the valves and valve seats.
The guys and gals with the high-compression muscle cars produced before the ban on lead had problems. I continued to drive the low-compression flat head engines on the "new" unleaded and had no problems. Through the years, Dodge "souped up" the flat head by increasing its compression ratio from 6.7:1. In 1955, they added valve inserts, so your C-3-PW has them.
OVER-SIMPLIFICATION: The final flat head 6 compression listed for the 1968, 251 cu.in. engine and was 7.5:1. The 383 cu.in. V-8 that was an option in the 1968 W100's and W200's had 9.2:1 and required regular grade gasoline.
If you have supercharged your flat head 6, the increased compression demands not only a very high-octane fuel, but also a very high tech additive to keep those valves happy.
If yours is not supercharged and you "want my worker truck to work for more than the 40-50K miles from the excessive breakdown of the non-leaded gas." follow Gordon's advice and find a shop that does not blame unleaded gas for problems in engines they have worked on.
One more thing… Please don't make me have to remember all this stuff about when I was young and gasoline was 19 cents a gallon.