: Now the question is: What is causing the low power output?

... but it's intermitent and subtle. The low power has always been "within
spec" as per runup, just always at the low end.

: Sounds a lot like a sticking valve, but I think I've done everything that can

: I am not an expert, but in my (one) experience with a stuck valve - I
: could hear it chatter when it stuck. It was not the kind of thing you
: could overlook. Perhaps there are other ways for valves to stick
: without chattering, but I thought I would at least provide you this
: datapoint.

: What are the compressions? Very low compression can be cause poor
: power output.

All compression tests have been excellent... generally 79/80 or 80/80. Once I
had one at 78/80. When the valves and rings seat up for a compression test, all is
good.

: Another possibility is a worn camshaft, and hence the inability to
: fully lift the valves. This results in low power output. On an
: engine that had low usage for its first 10 years SMOH, it should be a
: concern. There are many archived threads on google groups discussing
: camshaft rust and the subsequent damage to the camshaft.

I've looked into those for years as a concern for this engine given its
history. When we had the jugs off last time, I looked at the cam carefully. I could
see no visible evidence of rusting, pitting, or spalling. The tappets (from what I
could see without splitting the case) looked good too. Besides, I cannot see how a
worn cam would suddenly become unworn 60 seconds after takeoff.

: Seeing any metal in the filter on oil changes? Do you do oil
: analysis? If so, this could help confirm the latter theory. Also, I
: believe there is a way to measure the valve lift and compare against
: tolerances to see if the cam and lifters are doing their job.

I do not send out for oil analysis, but I cut open the filter. Never more
than a couple tiny specs of metal or carbon in the filter.... certainly within
"normal" limits.

I'm planning on measuring the lift when I've got the covers off. I need to
build some sort of jig for a dial indicator and figure out a way to drain the lifters
of all oil. Does anyone know what the lift is supposed to be? IIRC it's not a
"normal" maintenance check item so it's not in the books.

Thanks for the comments, though... I think we're in the same spot.

-Cory


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* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
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