Prop position

[Dan Luke]

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

[Nathan Young]

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.

[Doug]

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.

[Dan Luke]

"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

[nrp]

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.

[Dan Luke]

"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

[Doug]

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 :-)

[Dan Luke]

"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?

[nrp]

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.

[[email protected]]

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

[[email protected]]

In rec.aviation.owning nrp > wrote:
: 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.

There was a thread on this awhile back. I'd concluded that at least on the PA28
like mine, the discrepancy is in the service manual itself. It calls for 10-2 IIRC, but
doesn't say if it's as viewed from the front or the rear. So, 50% of them out there are on
one way, and the others are 60 degrees off. I *still* don't know which is right.

-Cory

--

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

[Steve Foley]

"Doug" > wrote in message
oups.com...
>
> The only other answer is some airplane elf came and reindexed your prop
> in the middle of the night :-)
>

May not be as strange as it sounds.

Maybe someone needed a prop. They stole one, put it on your plane and stole
yours. That way the one reported as stolen is on your plane, which you may
never find out about. Mr prop theif winds up with yours, which never gets
reported.

[[email protected]]

I'm pretty sure where the prop stops doesn't measure anything.
How do you know it stopped in the same place "horizontally"
each time? There are at least two possibilities.

Why would the prop stop in a preferential position anyway?
Seems like it would be on any one of the 4 compression strokes.

I'm also convinced that even the differential compression
check doesn't show what you really want to know.
The rings are AC coupled, tho less so in the Lycomings.

So I'd guess one would need something worse to worry
about. Maybe price of gas or user fees!

Bill Hale

[Dave Butler]

wrote:
> I'm pretty sure where the prop stops doesn't measure anything.
> How do you know it stopped in the same place "horizontally"
> each time? There are at least two possibilities.

Right, unless you can somehow distinguish the two blades.

>
> Why would the prop stop in a preferential position anyway?
> Seems like it would be on any one of the 4 compression strokes.

There are 4 cylinders, and each one has a compression stroke every 2 revolutions
of the crankshaft. That makes 2 compression strokes per revolution. The prop
stops in one of two places, which are indistinguishable unless you can somehow
distinguish the two blades.

>
> I'm also convinced that even the differential compression
> check doesn't show what you really want to know.
> The rings are AC coupled, tho less so in the Lycomings.

What does this mean: "The rings are AC coupled"?

>
> So I'd guess one would need something worse to worry
> about. Maybe price of gas or user fees!

Agreed. It's fun to think about, though, and if there's a sudden change in
behavior, I'd want to know what changed.

[Nathan Young]

On Mon, 20 Mar 2006 19:57:03 +0000 (UTC),
wrote:

>In rec.aviation.owning nrp > wrote:
>: 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.
>
> There was a thread on this awhile back. I'd concluded that at least on the PA28
>like mine, the discrepancy is in the service manual itself. It calls for 10-2 IIRC, but
>doesn't say if it's as viewed from the front or the rear. So, 50% of them out there are on
>one way, and the others are 60 degrees off. I *still* don't know which is right.

Mine stops with the prop @ 2 O'Clock as viewed from within the cabin.

[Brien K. Meehan]

Did your propposition involve 10 o'clock and 4 o'clock?

.... or was it something about being horizontal?

[[email protected]]

>>>>Did your propposition involve 10 o'clock and 4 o'clock?

.... or was it something about being horizontal?<<<<

LOL. The usual "approach" has something to do with picking her up at 10
and dropping her off at 4 <G>

[Montblack]

wrote)
> ... or was it something about being horizontal?<<<<
>
> LOL. The usual "approach" has something to do with picking her up at 10
> and dropping her off at 4 <G>


"I'm not that kind of girl - SLAP!"

"Contact."


Montblack :-)

[Dan Luke]

"Steve Foley" > wrote in message
news:BSDTf.6447$092.3203@trndny04...
> "Doug" > wrote in message
> oups.com...
>>
>> The only other answer is some airplane elf came and reindexed your prop
>> in the middle of the night :-)
>>
>
> May not be as strange as it sounds.
>
> Maybe someone needed a prop. They stole one, put it on your plane and
> stole
> yours. That way the one reported as stolen is on your plane, which you may
> never find out about. Mr prop theif winds up with yours, which never gets
> reported.

Nope; nice try, though. I'd already made 3 stops that day in which
everything appeared normal.

[Dan Luke]

> wrote:

> I'm pretty sure where the prop stops doesn't measure anything.
> How do you know it stopped in the same place "horizontally"
> each time?

Because I've been watching it carefully for 3 years.

A prop that stops in an unusual position can indicate a cylinder with poor
compression, as I discovered when I had cylinder trouble 3 years ago.

> There are at least two possibilities.
>
> Why would the prop stop in a preferential position anyway?
> Seems like it would be on any one of the 4 compression strokes.

Becaues of the crankshaft geometry of the horizonally-opposed Lyc. O-360,
the prop will stop in the same compass position every time as it bounces
back from the last TDC.

> I'm also convinced that even the differential compression
> check doesn't show what you really want to know.
> The rings are AC coupled, tho less so in the Lycomings.

?

> So I'd guess one would need something worse to worry
> about. Maybe price of gas or user fees!

No. Something has changed, and that's something to worry about.

--
Dan
C172RG at BFM

[Orval Fairbairn]

In article >,
"Dan Luke" > wrote:

> "Steve Foley" > wrote in message
> news:BSDTf.6447$092.3203@trndny04...
> > "Doug" > wrote in message
> > oups.com...
> >>
> >> The only other answer is some airplane elf came and reindexed your prop
> >> in the middle of the night :-)
> >>
> >
> > May not be as strange as it sounds.
> >
> > Maybe someone needed a prop. They stole one, put it on your plane and
> > stole
> > yours. That way the one reported as stolen is on your plane, which you may
> > never find out about. Mr prop theif winds up with yours, which never gets
> > reported.
>
> Nope; nice try, though. I'd already made 3 stops that day in which
> everything appeared normal.

I would not be too concerned about it. Remember -- the rings rotate in
their lands and can sometimes end up with all the gaps lined up, thus
changing the effective compression. This appears to be the case here,
since the prop is now stopping in the usual place.

To add fat to the fire: is it always the same blade on the same side, or
do they swap?

[Ben Smith]

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

How did that happen, did you pull the 'we're out of gas' trick? :)

[Montblack]

("Ben Smith" wrote)
> >I once prop-positioned a cutie on the ramp... If you must know, I crashed
> >and burned... :-(

> How did that happen, did you pull the 'we're out of gas' trick? :)


She informed him of the "Pop-up" TFR:
Sorry, can't.
Huh?
The "President" is coming for a visit.
Huh?
The "P-R-E-S-I-D-E-N-T" is visiting ...for a week.
Oh .....<pause> ....OH! ....<pause> .....Doh!


Montblack
That's alright, we can still cuddle.
Yeah, ok, sure ...whatever.

[Dictionary.com]
yeah
adv : not only so, but; "I therein do rejoice, yea, and will rejoice" <g>

[Dan Luke]

"Orval Fairbairn" wrote:


> I would not be too concerned about it. Remember -- the rings rotate in
> their lands and can sometimes end up with all the gaps lined up, thus
> changing the effective compression. This appears to be the case here,
> since the prop is now stopping in the usual place.

But it's not; that's the problem.

It stopped in the usual place 3 times at 3 different shutdowns Sunday, then
stopped in the new place when I got home Sunday night.

> To add fat to the fire: is it always the same blade on the same side, or
> do they swap?

They swap.

--
Dan
C-172RG at BFM

[Dan Luke]

Update:

I went to the airport first thing this morning to turn the prop with the
engine cold. As before, I felt good compression at each cylinder, and the
prop stopped at 02:30/04:30.

So I ran the engine for 3-4 minutes, just to get the oil a little warm, and
shut it down. Voila': the prop stopped at its usual 09:00/03:00 position.

I don't know WTF to think, now.

Wait a minute, yes I do: I think I'll have a couple of Coronas and forget
about it..

--
Dan
C-172RG at BFM

[nrp]

Dan -

Does the engine always feel tight only when hot? If so, as a
precaution, do an oil analysis next change or next time the cowl is
off. Don't waste money on a more formal compression test.

You don't have top end trouble, but you just might have a problem at
the bottom end.

[Dan Luke]

"nrp" > wrote in message
> Dan -
>
> Does the engine always feel tight only when hot?

No.

> If so, as a
> precaution, do an oil analysis next change or next time the cowl is
> off. Don't waste money on a more formal compression test.
>
> You don't have top end trouble, but you just might have a problem at
> the bottom end.

Like what?

[[email protected]]

> > You don't have top end trouble, but you just might have a problem at
> > the bottom end.
>


I mentioned that to my wife a few days back... and got slapped...

[nrp]

Like what? Possibly, and I want to emphasize just possibly - a shelled
out camshaft system contaminating the crank bearings such that they
shrink onto the crankshaft on cooldown. An oil filter check (assuming
there is one) would also show if something is shelling out. Maybe even
just looking critically at the oil on the dipstick would show aluminum
or steel "paint" immediately after a shutdown.