"Kyle Boatright" wrote in message ...

How about a bad camshaft or follower? You could pull the valve covers and
plugs, then rotate the engine by hand and measure the movement of the rocker
arms to see if you have a worn cam lobe or follower. This is a simple way
to determine if there is a valve that doesn't get the same lift as the
others...

By the way, do you have RPM and MP data on the engine? Are you gettting the
reduced performance you quote when running at 75% per the lycoming
rpm/mp/temp charts?

Is it possible that your tach is off or your MP is low because of a clogged
air filter or some other induction problem?

KB


Thanks to everyone, so far for the excellent suggestions. Kyle: we are
gonna check for valve timing, and will pursue looking for a worn cam
lobe or follower. Good suggestion, thanks.

My tach has been confirmed by an optical tach, so those are both spot
on. MP? One of the things we are wondering about is an induction
problem, but so far that doesn't look likley. Regarding your comment
about RPM/MP data. Yes, I have RPM and MP data, and can cruise at the
appropriate RPM and MP for 75% power at a given altitude and
temperature. However, if the engine was somehow "derated" to 180 HP,
wouldn't I just be getting 75% of 180HP? The constant speed prop is
going to adapt to the power output to maintain the appropriate RPM,
and the MP is just the MP.

One of the things that lead me to this group was the comment elsewhere
that IO 360 were hot running engines. Mine is pretty cool running.
Hence my suspicion that I am not producing the horsepower!

Thanks again, all.

One hopes we'll have an answer in a few days!

Jim