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[email protected] · January 9th 06, 03:57 PM posted to rec.aviation.owning,rec.aviation.piloting

wrote:
In rec.aviation.owning nrp wrote:
: At that time, we consulted the service manual, which
: states 8-2.

: Maybe that's from the Piper legal dept to discourage hand
: propping.........!

Possibly, but that part of the book has been there forever. The trouble with
the 8-2 position (from the front) was that is was unobtainable IIRC. It was a nice,
clean 30 degrees off in either direction. Doesn't exactly give one a warm fuzzy when
the official service instructions are impossible to follow.

-Cory

The 8-2 (or more closely 7:30--1:30) IS appropriate for hand
propping. The position given by Service Manuals is at TDC so that the
prop will be at about 10:00 when ready to hand prop with the piston
partway up thye compression stroke.

The three-blade props used on some larger engines can cause
mysterious vibrations unique to them. Some Cessna 185s, for example,
had a habit of throwing off the alternator belt. The problem was
normally cured by removing the prop and rotating it 180 degrees. Don't
ask me why.

Some engines have problems with the pulsating airflow off the prop
blades striking the air intake at just the wrong time and upsetting air
and fuel flows in the carb. (Remember that the airflow through the carb
isn't particularly constant, as it accellerates and decellerates with
intake valves opening and closing.) This is readily apparent on some
older 182s, on which the air cleaner comes off with the cowling, and
running the engine with the cowl off will make for a rough-running
engine. The air cleaner damps some of the pulsation. Re-indexing the
prop might improve smoothness and maybe performance.

Dan