Hi,
Unleaded gas is a continuous source of discussion with old car folks.
Unleaded fuel will cause valve seat recession in a engine without hardened
valve seats i.e. valve seats in the cast iron of the head rather than in
hardened valve seat inserts. The recession is only a problem with engines
in continuous service, like buses or taxis or daily long-commute drivers.
I've talked to guys who have used non-leaded fuel and non-hardened valve
seats in their old cars for years without problems.
I have an old Chevy truck with a 400 c.i.d. small block V8 that was rebuilt
without hardened valve seats in the early eighties. At that time, machine
shops were still a little wary of installing hardened seats as they
occassionally came loose. I've put about 70,000 miles on it and, although
it is getting a little seedy, it still runs fine.
The rule of thumb seems to be: If you have remove the head to do a valve
job, by all means have hardened valve seats installed. Until that time,
don't worry about it.
At 06:03 PM 7/15/97 PDT, you wrote:
>
>Chuck Vandergraaf writes
>
>>A second question concerns the use of unleaded gas in an engine that was
>>designed for leaded gas. I've been led (no pun intended) to believe
>>that lead (Pb) in gas hardens the valves and that the replacement,
>>manganese (Mn), will eventually lead to problems.
>
>The issue is that the valve seats on older engines are not hardened. Lead
>in the fuel forms a protective layer, especially in the exhaust port. Such
>an engine will suffer valve seat wear when run on unleaded fuel. I am not
>clear on the extent of the wear, or on the influence of substitute
>additives.
>
>98 Octane leaded fuel is still available in the UK as it was only in 1988 (I
>think) that cars had to be able to run on 95Octane unleaded and only in
>1993 that CATs became compulsory on new cars. Advice given by some
>manufacturers (e.g. GM) for those who wished to change was to run one
>tankful leaded in four so maybe an occasional treatment would be enough.
>
>Dave Vodden
>1992 Plus 4 4 seater
>Hampshire UK.
>
Howard Clark
P.O. Box 413
Brookston, IN 47923
'65 +4 2 str
'36 Cord 810
'47 Ford Street Rod
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