Alan
I have a different point of view on this subject. One which might well
start a new debate.
Something like 20 years ago there was a great panic amongst UK users of
older cars when leaded fuel was being withdrawn. Many owners of 100s
asked me what they should do and my suggestion was; do nothing.
Around that time the Vintage Sports Car Club published a 25 page
document which was the result of significant testing that they had
carried out on older engines.
It was titled
Valve Seat Recession
Use of Unleaded Gasoline in Older Engines
It was very comprehensive but the conclusion was that for low
compression, medium tuned engines such at the 100 the recession due to
the lack of lead on the valve seat was likely to be virtually non
existent.
Based on this many 100s that I know are still running around without
changing valve seats without problems 20 years later.
Now to this I can add another point. As we know the 100 head is very
prone to cracking across valve seats. One owner I know added seats to a
perfectly good head but soon found the a fatal crack had appeared beyond
the valve insert. The conclusion was that as the seat has to fitted by
interference fit, the extra pressure had caused the crack.
My final point is that if one does get seat recession then all that is
happening is that the part of the head that is being ground away would
have to be cut away later when fitting a seat; so why bother.
Regards
>While you are at it, have the head set up to run on unleaded.
>
--
John Harper
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