Turning the Prop Over as Part of Preflight?

"O. Sami Saydjari" wrote:

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

How old is this book? (I'm guessing that it dates from the 30s or 40s).

What do folks on this newsgroup think of that advice?

Sounds like he's talking about radial engines. Radials indeed tend to collect oil in
the lower two or three cylinders. Most radial owners pull the prop through a few
times to check for hydraulic lock. The old "inverted" engines like the Ranger series
sometimes presented similar problems. This is not a problem with the horizontally
opposed engines behind which most of us fly.

Does anyone out there do this routinely?

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.

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

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.

Could fuel actually collect in the cylinders as suggested?

Not in most light planes. The carb is usually behind or under the engine. Even if gas
did flow through the carb (and there are several valves that usually prevent this),
the fuel would just fall out the throat of the carb.

Why would the fuel not just evaporate?

If raw gas pooled in the cylinders or induction system, the saturation point of the
air in there would be reached rather quickly.

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

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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