Prop position

I'm talking about where the prop stops when I shut down the engine. What
would cause a 2-blade, constant speed prop on a Lyc. O-360 to suddenly begin
stopping in a different position than it had every time for the last 3
years?

My prop has always stopped parallel to the pavement until last night, when
it stopped at 10:30/4:30 position. I pulled it through two complete
revolutions and compressions felt ok.

--
Dan
C172RG at BFM

On Mon, 20 Mar 2006 07:26:24 -0600, "Dan Luke"
wrote:

I'm talking about where the prop stops when I shut down the engine. What
would cause a 2-blade, constant speed prop on a Lyc. O-360 to suddenly begin
stopping in a different position than it had every time for the last 3
years?

My prop has always stopped parallel to the pavement until last night, when
it stopped at 10:30/4:30 position. I pulled it through two complete
revolutions and compressions felt ok.

If I have the engine idle-ing less at or less than 1000RPM, the prop
on the Lyc O-360-A4A on my PA28-180 stops in the same position 95% of
the time.

If the RPM is higher than 1000 (before killing the mixture), it
(frequently) stops at a different position.

Get a compression test. Seriously. One of your cylinders (the one that
it stops on) very well may have low compression. Something has changed.
I'd check it out.

"Doug" wrote:

Get a compression test. Seriously. One of your cylinders (the one that
it stops on) very well may have low compression. Something has changed.
I'd check it out.

That's what I thought at first, but how come it stops in the new place no
matter whch cylinder is coming up on compression? And if a cylinder is
really going, how come I can feel compression on each cylinder as I swing
the prop?

I've had soft cylinders before that caused the prop to stop in an unusual
position; this doesn't seem the same.

--
Dan
C172RG at BFM

My suggestion - Could just be lower internal friction due to oil
viscosity, or even the engine simply breaking in. I'd almost be more
concerned about why it always stopped horizontally, as at least most
broken-in 4 cylinder engines stop with the prop at 45 degrees (10:30).


First verify that the mags actually do indeed shut off, then kill the
engine with the mixture, and do a hand prop to see if all cylinders
feel the same. Only if there is a noticeable difference, get a
compression check.

"nrp" wrote:

My suggestion - Could just be lower internal friction due to oil
viscosity, or even the engine simply breaking in.

The engine is well broken in. 300+ hrs. since a top overhaul.

I'd almost be more
concerned about why it always stopped horizontally, as at least most
broken-in 4 cylinder engines stop with the prop at 45 degrees (10:30).

Really? This seems to vary among the O-320 and O-360 engined aircraft I see
on the ramp. I'll do a more careful survey next time I'm out there.

First verify that the mags actually do indeed shut off, then kill the
engine with the mixture, and do a hand prop to see if all cylinders
feel the same. Only if there is a noticeable difference, get a
compression check.

Did that. They feel the same.

--
Dan
C172RG at BFM

Well the only way to find out is to get a compression test. I don't
know the answer to your delimna, and neither do you. "By hand"
compression tests are not worth much. Do it with a guage.

The only other answer is some airplane elf came and reindexed your prop
in the middle of the night :-)

"Doug" wrote in message
oups.com...
Well the only way to find out is to get a compression test. I don't
know the answer to your delimna, and neither do you. "By hand"
compression tests are not worth much. Do it with a guage.

The only other answer is some airplane elf came and reindexed your prop
in the middle of the night :-)


I was afraid that was the answer. It's *got* to be a cylinder or two,
doesn't it?

More thoughts -

Your prop just might be indexed correctly but differently than the ones
I'm recalling. That seems to be a snake oil thing with different
aircraft.

Another lo-cost check would be to do an oil analysis on a sample. I
know of an engine that would get really stiff when warm that had a bad
cam lobe & misc bearing contamination. It would free up on cooldown.

I contend the equal cylinder-feel-on-hand-prop test is an effective way
to check out the upper end of an engine, although it would not uncover
any lower end mayhem. An oil analysis is the cheapest way to check or
track the lower end. Be sure to take the sample correctly though.

I once prop-positioned a cutie on the ramp... If you must know, I
crashed and burned... :-(