"Robert Palmer" <rbpalmer_nrt@hotmail.com> wrote:
>Yep that was me - The second cylinder was at 35# - and the exhaust valve in
>that cylinder has a couple of triangular wedges cut out of the edges.
Which usually means the valve guides are shot...BTDT...got the T-shirt....
In my case, I was #4 exhaust - I was told by the machinist that I was about
25 miles from catastrophic failure. The geometry of the tappets and rocker
arms is such that the valves actually rotate slowly in place. (Put a dab
of paint on one and you can watch it do its little dance with a strobe
light.) If the bore of the valve guide gets a bit loose, the valve shaft
will tip ever-so-slightly out of vetrical and instead of rotating, it will
contact at one place one the head first on each closure. In addition to
the simple repetitive stress, this allows a 'hot spot' to build up,
resulting in the familiar, pie-shaped cracks.
If your machine shop is up to snuff, ask them to knurl the guides, which
allows them to keep/hold more oil. My machinist did this as a matter of
course, but he was of the 'old school'...sadly, he has retired....
Cheers
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