"Faure, Marin" <marin.faure@boeing.com> wrote:
>I'm thinking that perhaps the unleaded fuel troll has
>finally caught up with me.
Not bad actually....I lasted about a dozen years or so between the exit of
leaded fuel (which virtually coincided with an engine rebuild *without*
stellite valves) and the recent head rebuild. And this was using marine
Re-Lead in every tank and an Ampco vapor-lubricator injecting Marvel into
the fuel load....
A couple of years ago, I redid the head even though it was only 60,000
miles after a major engine rebuild. I knew compression in #4 was dropping
and it developed that distinctive, rythmic putt-putt sound out the exhaust.
Towards the end, the exhaust miss was hard to ignore, and by the time I
pulled the head, there was a wedge-shaped crack in #4 exhaust. The machine
shop guy said I was 25 miles from catastrophic failure....
During the last engine rebuild, the only thing (other than swapping over to
stellite valves, of course) that was not addressed was the valve guides.
The valves are designed so that in use, they rotate slightly, giving even
wear and more importantly, even cooling. With worn valve guides, the valve
will tip ever-so-slightly, causing it to touch at one spot before it seats
completely. It is this one hot spot that causes the familiar, pie-shaped
crack.
Buy stellite exhaust valves from one of the usual suppliers. Let the local
machine shop source the stellite valve seats, as he will have the
proprietary cutters to install these.
Cheers
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This archive was generated by hypermail 2b30 : Fri Nov 15 2002 - 10:28:20 EST