Turning the Prop Over as Part of Preflight?

I've been reading the POH for an older Piper Apache 150 lately and it
suggests pulling the prop through several times in cold weather. (I'm just
assuming to circulate some oil through the engine and prop hub, but then
again just how much would actually circulate when it's cold??) Although the
Apache has Lycoming engines, I too wonder if this is a carry through from
the radial days.
Jim Burns

"O. Sami Saydjari" wrote in message
...
In reading a booked called "Design for Safety", by David Thurston, he
advises owners to "turn the propeller over by hand three or four times
during preflight if the airplane has been standing for half a day or
longer." [p169]

His rationale is as follows. "When an engine has been standing for
awhile and has not been pulled through by hand prior to starting, an
accident could result if fuel or oil has collected in the cylinders.
When the engine fires, trapped fluids can cause bent piston rods,
cracked cylinders, or a damaged crankshaft. Althouogh such accidents
might not cause bodily injury, they surely can harm one's budget and can
beavoided by proper preflight procedures. It is also possible for
damage of this type to remain hidden until something fails in flight"
[pp 147-148].

I am quite surprised that this is the first I have heard such advice.

What do folks on this newsgroup think of that advice?

Does anyone out there do this routinely?

If so, what is the proper procedure? Do you just turn the prop slowly
in the direction the prop normally turns?

Could fuel actually collect in the cylinders as suggested? Why would
the fuel not just evaporate?

-Sami
M2057M, Piper Turbo Arrow III

G.R. Patterson III wrote:
: I frequently pull the prop through four times to check compression. This also makes
: it slightly easier to start in Winter by breaking the gummy oil bond that tends to
: form between the rings and cylinder walls.
: Make sure the mags are off and mixture at lean cutoff. Pull the prop in the direction
: it normally turns. Stay out of the plane of the prop. My prop is indexed to stop
: straight up and down. When I pull the prop through, I pull the lower blade up.
:

I generally pull my Lycoming O-360 through at least 4 blades (all compression
strokes) to verify that I've got the adequate and roughly equal on all strokes. I got
in the habit of doing this after a recent top overhaul, to check on the status of the
break-in.

In addition to the mags being switched off, mixture leaned, and never primed,
I *always* pull it through as if I were hand-propping it (expecting it to fire off).
If you ever once pull it through without that thought, you're looking to have a new
nickname.

That said, it probably doesn't do much for the engine, good or bad. In cold
weather, just nudging the prop would do the same "loosening" as pulling it through a
few blades. If your oil truly is that gummy, though, better rethink your oil-changing
invervals...

FWIW,
-Cory

--
************************************************** ***********************
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* - learn what you don't know, *
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Jim Burns wrote:

(I'm just
assuming to circulate some oil through the engine and prop hub, but then
again just how much would actually circulate when it's cold??)

Pulling the prop through will do absolutely nothing to circulate oil. It usually
takes several seconds for the oil pressure gauge to come off the peg after engine
start, and that's at about 1,000 rpm.

George Patterson
I childproofed my house, but they *still* get in.

On Mon, 17 May 2004 16:20:27 GMT, Chris Kennedy
wrote:

O. Sami Saydjari wrote:

The book appears to have been published in 1995. He does not seem to
say anywhere that the advice is unique to radials.

Hydraulic lock on radials without clean kits is well understood, but for
wet sump boxer engines like we generally fly behind the advice not only
makes no sense, it's contrary to Lycoming's current recommendations.
With the oil sump under beneath the engine there's simply no mechanism
for lock to occur, unless you tend to park your aircraft inverted.

About the only mechanism I can imagine for causing something like this
would be on some injected engines, where hitting the boost pump and
ramming the mixture full forward while the engine is stopped will dump
gobs of fuel into the intake runners. While much of it will eventually

That's the way I start mine.

come pouring out the air cleaner it's not hard to imagine getting

None of it comes out the air cleaner, but it sure do run out the
exhaust stacks. OTOH, Boost pump on for a count of three (or even
10)hardly qualifies for enough to block a cylinder. Course the count
of ten might start a fire. :-))

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com

unlucky and having one cylinder with an intake valve open. Hardly seems
the basis for turning the engine over by hand as a standard procedure.

"O. Sami Saydjari" wrote in message ...
The book appears to have been published in 1995. He does not seem to
say anywhere that the advice is unique to radials.

-Sami

It certainly sounds like the old radial hydro-lock check. Since the
oil sump and fuel system of your average horizontally opposed engine
are lower than the cylinders, I can't see where this procedure would
be applicable. For radials, on the other hand, it's a very common
procedure.

BTW - Was that you I saw on "Frontline" last week?

John Galban=====N4BQ (PA28-180)

I always pull the prop through at least two revolutions - just to make
sure there is compression on all six cylinders.

As for there being no need to do so with opposed engines, I vividly recall
a pilot telling the story about what happened to him. It seems he had just
bought a new (to him) airplane, and was trying it out. It was an early
model Cessna 210, with fuel injection. He decided to find out how fast it
was, and laid out a course between two points along the Southern California
coastline. Then he flew the course with the throttle and prop firewalled.
To cancel the efect of wind, he planned to fly it in both directions. The
outbound pass went well, but on the way back there was suddenly a loud bang,
and the view out the windshield went black (covered with oil). Down he went,
sighting out the side windows as best he could. He ditched it in the ocean,
and managed to get out before it sank.

It gets worse. As there were no boats within sight, he swam to the beach.
There was no one there either. Then a boat came along, so he swam out to
it. About that time, some rescuers showed up on the beach, so he swam
back again. Later, the plane was recovered. They found that a cylinder
had blown off the engine, right through the cowling. The analysis was
hydraulic lock, caused by a leaky injector. The theory was that the
cylinder had filled with gasoline, and was overstressed when the engine
was started. It could have happened long before the final flight.

Worst of all, he had neglected to obtain insurance for his new toy. The
only good news in this event is that he walked (or rather swam) away
with only a minor injury.


David Johnson

Jim Burns wrote:

I've been reading the POH for an older Piper Apache 150 lately and it
suggests pulling the prop through several times in cold weather. (I'm just
assuming to circulate some oil through the engine and prop hub, but then
again just how much would actually circulate when it's cold??) Although the
Apache has Lycoming engines, I too wonder if this is a carry through from
the radial days.

But the point should be, we need to try to elevate ourselves from the
50-year-old advice in those old references, and try to do what makes
sense today, with the advances in lubricating oils which were not
available when those old instructions were written.

BTW - Was that you I saw on "Frontline" last week?


Yes, it was.

O. Sami Saydjari wrote:

BTW - Was that you I saw on "Frontline" last week?


Yes, it was.


This cries out for further explanation! Which Frontline episode? What was the
context?

Dave
Remove SHIRT to reply directly.

The program is called "Cyberwar" and can be viewed at
http://www.pbs.org/wgbh/pages/frontline/shows/cyberwar/

You can see a more extended interview under the "interviews" link.

-Sami

Dave Butler wrote:
O. Sami Saydjari wrote:


BTW - Was that you I saw on "Frontline" last week?


Yes, it was.


This cries out for further explanation! Which Frontline episode? What
was the context?

Dave
Remove SHIRT to reply directly.