On 15 Sep 2009 at 11:43, akgraves@cox.net wrote:
> Then I noticed a gaping hole in the #6 exhaust valve...
> My question is what could have caused that?
I'm sure one of our mashinist experts will answer, and maybe
contradict me (in which case I'll learn something).
Several thoughts come to mind. A burned exhaust valve is typically
caused by it being set too tight. Of course, with a pushrod engine
when you remove and replace the head the valves need total re-
adjustment. Then when (if) you re-torque it that tightens them up by
pulling the head down onto the block, so you need to to adjust them
again. Even so, 100 miles is a short distance to burn a valve unless
it was damaged to begin with. Also too early ignition timing and too
low fool octane will make the engine internals run hotter and
exaggerate the burning.
Even so, that would not necessarily cause the loss of so much oil in
only 100 miles unless it was being pulled up past the rings and not
being blown or scavenged back down. A more likely cause would be a
badly worn valve guide, which could similarly have contributed to the
valve not closing against it seat properly. As I recall, a typical
sign of worn valve guides is that after you sit at idle for a few
minutes such as for a stoplight and then pull away, the exhaust blows
a lot of oil smoke (which is blue-ish), though it does not otherwise
seem to burn oil excessively. While you have the head off and are
dealing with the valve, check (or have a good machine shop) check the
guide and seat too. Might as well check all of them!
--
Jim Muller
jimmuller@rcn.com
'80 Spitfire, '70 GT6+
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