Chuck wrote:
: Hi guys & gals,

: I purchased an older Cherokee 180 with a Lycoming O-360A4A and
: Sensitech propeller. Unfortunately, I'm not sure on of the prop model
: as I haven't pulled the cone yet.

: Since I purchased my Cherokee, there has been a slight vibration in it
: while running and flying. The first mechanic I had went for a ride
: with me and immediately said the prop needed a "balance" job.

I've got the same plane/engine/prop combination. I had to change the
alternator belt a few months ago and my mechanic and I decided that the prop wasn't
indexed properly. The prop has a 6-bolt pattern so it could be put on incorrectly at
60 degree increments. The compression stroke used to put TDC with the prop at 3-9
o'clock. Now, it's more like 1-7 o-clock. It significantly reduced the vibration on
mine.

I know that the prop is supposed to be on only one way. The really annoying
thing is that the service manual for the plane says TDC should be at 2-8 o-clock....
exactly halfway between the two possible positions. My mechanic and I puzzled over it
for awhile, but eventually decided (from the way other Cherokees' had their props
indexed) that it should be moved. I can see why the previous owner may have put it on
the other way, but since the vibration is much reduced now I believe this way is
correct. I've also heard rumors about pigs flying and a slight manifold pressure
increase from having the carb air induction in the correct position to get a bit of
propwash. Not sure I buy it, but the new position would seem to make that more
possible (fiberglass clamshell cowling on mine).

Seems stupid to make it possible to put the prop on wrong, but they did.
Pity, too... it was much easier (and safer) to pull the prop through the compression
stroke at the 3-9 o'clock position.

-Cory

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