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Not to be unduly snappish, but you gotta measure it to find out what it really
is.
What SHOULD it be? Depends on whom you ask.
The manual says 0.020-0.021" Some guys run less and get away with it.
The B18 spec is 0.018" and I set the valves on my 164 (B30A) at that for
a cross country trip and got cracked exhaust valve seats on 4 of the 6.
B20 and B30 use the same valve gear, so I theorize that the B18's larger
valve stems may conduct more heat away and transfer it to the guides better
and thus get less thermal expansion of length of the valve stem.
In any case I went back to 0.020" and have not had the same problem again.
--
George Downs, Bartlesville, Heart of the USA!
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