In addition to the other responses, all of which are worth checking, I
can add a possiblity that happened to me that might possibly be worth
checking. Shortly after take-off on a flight last year, I thought I
noticed a small vibration in the engine. Very small. The only way I
could tell for sure that something was wrong, was that it also was
about 100 rpm down on power when I checked using a full power run in
level flight. I returned to the field. A very good decision as it
turned out. After much advice from others as to what the reason was
(the engine idled perfectly, no signs of problems), I decided to do a
ground up exam with the mark 1 eyeball, looking for telltale leaks,
etc. I noticed a small trace of oil around the base of one cylinder.
More like a dark ring where the cylinder bolts to the case. Suddenly a
sight I will never forget jumped out at me. A close look at the
cylinder base and I noticed that the top 1/2" stud, and 2 3/8" studs
were broken off clean as a whistle with the top of the cylinder base
flange, the nuts were gone! It almost looked like it was supposed to be
that way. Upon removing the baffles, I noticed that a 1/2" and 3/8"
stud on the bottom of the cylinder were also broken. I had only 2, 1/2"
and 1, 3/8" nuts holding the cylinder on! This was allowing the
cylinder to stretch a little under stress, and therfore the valves were
not opening properly, and thus the small power loss. This engine had
1200 trouble free hours since OH. (Lyc O-360).
In investigating causes of this, one of the reasons given for
loose or broken studs, is having too thick a layer of paint or primer
on the cylinder base flange. This puts a layer of paint between the
flange and the nut, preventing proper tightening. This paint gets worn
away after 100 or so hours of operation, causing a loose cylinder.
So, maybe you should check for a loose cylinder.

Also, I agree very much with those that say do not fly again until you
have figured out what is wrong. Returning to the field probably saved
my life. The NTSB accident reports show many planes have had cylinders
come off in flight, like the Saratoga that landed in a soybean field in
Wisconsin.

Regards,
Bud

wrote:
Do you ever have those days where you're just scratching your head?

I've got an IO-540 (strapped to the right side of an E-Model Piper
Aztec) that won't generate full RPM. Let me describe the takeoff
sequence.

During the run-up, both the feather check and the mag check are normal
(done at 1700 RPM and 2000 RPM respectively.) During the takeoff roll,
all seems normal, but initial climb is sluggish (not alarmingly so, but
just enough to notice). The right side RPM indicator shows about 2450
RPM, while the left side is showing just above 2600 RPM (as usual).

When setting climb power, bringing the power back to 25-inches on both
sides will not cause the left side to lose measurable RPM, but the
right side loses about 100. Synchronizing the propellers does cause the
"beating" to go away when the RPM indicators indicate the same RPM, so
I'm confident that the RPM gauge is reading correctly.

During the initial tear down, it was noticed that the set-screw for the
right governor was set at about as high an RPM as possible. So the
initial feeling was that the governor was having a bad day.

So far, we've:
1. Sent he governor out for overhaul. (Prop shop reported that it was
fine.)
2. Swapped the propellers between the engines. (Problem does not follow
the propeller.)
3. Swapped the governors between the engines. (Problem does not follow
the governor.)
4. Verified full travel on the propeller controls (both in the cockpit
and at the governor).

The tech reps are suggesting that we send the engine back to Mattituck
(it's a factory remanufactured engine which has been "Mattitucked" with
about 100 hours on it), but I get the feeling that the tech reps and
mechanics are essentially in guessing mode.

Does anyone have any suggestions on what else to think about before we
pull the engine?

Thanks!

-Rob