John :
Without meaning to sow any more confusion on an already confused issue,
I'd like to point out that it is possible to harden cast iron exhaust
seats. Many (if not all) American cars use this method on cast iron
heads, since it allows the seats to still be cast as part of the head,
saving money. Some people will look at the insert-less heads and assert
"Those must be soft seats". To further add to the confusion, on some
engines the hardening is thin enough to be ground through when grinding
the seats.
Since I know of no practical way to distinguish any of these conditions,
the recommended course is still to wait until you need to 'do' the head
anyway, then install hardened exhaust seat inserts as part of the
rebuild.
Randall
jonmac wrote:
> <snip>
> All that said, there is evidence that some cars continued to
> use 'soft' valve seats until quite recently (prior to April
> '89) and this does nothing to clear a somewhat muddied
> picture.
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