Old Wives Tale. The only difference in an engine designed for leaded vs.
unleaded fuel is the way the bottom of the valve guide is cut. For leaded,
they cut a square shoulder into the bottom so the lead that collects on the
stem gets scraped off and rolled up into a donut to lubricate the valve. For
unleaded its cut with a taper to prevent gauling the valve. The pitting is
caused by detonation which can be controlled either by retarding the timing
a bit or using a higher octane fuel.

"FRANKWBELL" wrote in message
...
In article , Jeepers
writes:

I thought Leaded fuel went out in the mid 70s. Why then do I need Leaded
fuel on a 1985 motor?

I don't know if this applies, but I have a 1985 Merc in-line 6. I don't
know
if this is a mechanic's urban legend of what, but here goes:

Shortly after we got the boat in 1995, one of the pistons came up pitted.
$700.00 later, the mechanic told me that the pitting was from the use of
unleaded regular (87 octane) fuel and that the motor had been designed to
use
regular leaded fuel (which was still available, he said, for marine use at
that
time).

He recommended using premium fuel to avoid future problems. As of the
last
tune up, last year, everything was still okay.

Frank Bell
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