Propeller "Clocking" & Rough Running?

jsharkey · #1 04-01-2010, 06:03 PM

At the weekend I changed the oil and rotated the propeller 60 deg so that the leading blade was at a +30 deg high position to make hand propping a practical if unlikely possibility. Prior to that it sat naturally at a -30 low position when the engine stopped. Since making the change the engine/prop seems to be running "rougher". Does that make sense or am I imagining things? The engine is a YO360-A1A with a Sensenich 72/85 FP aluminum prop. Tach time is about 23 hours.

Jim Sharkey
RV6 - Phase 1

gasman · #2 04-01-2010, 07:19 PM

The prop on my 0320 Piper was removed to replace the backing plate. They then proceeded to install the prop as a 160 hp instead of the 150 hp that my Warrior was.

As soon as I got it up to cruse, I knew that something was wrong. Prop was at 12:00. I removed it and set it back to 10:00 per Piper service manual............

It's now smoothe as silk.

Geico266 · #3 04-01-2010, 07:21 PM

Have you dynamically balanced the prop / engine?

jsharkey · #4 04-01-2010, 07:23 PM

Quote:

Originally Posted by Geico266

Have you dynamically balanced the prop / engine?

Nope - but it was as smooth as silk before I moved it. Just wondered what the reason was?

osxuser · #5 04-01-2010, 10:52 PM

For propping, you don't want the blade to sit "naturally" at 30? high... you want it to come to the top of the compression stroke at 30? high.

Yes, your engine cares where the prop blades are. Why I don't know.

Hope the first helps.

turbo · #6 04-02-2010, 02:12 AM

it 180. see if it smooths out there. turbo

Kahuna · #7 04-02-2010, 05:40 AM

Quote:

Originally Posted by osxuser

....Yes, your engine cares where the prop blades are....
.

This is not true. Suggest searching prop clocking.
Some things do care, the engine is not one of them.

jsharkey · #8 04-02-2010, 08:39 AM

I may have placed the prop at 90 deg to the crank plane. The other options are +/- 30 deg.

Does it make sense that it would run smoother when not at 90 deg?

aerhed · #9 04-02-2010, 09:17 AM

Theoretically, I think the engine should not care. Like a big flywheel. But, they do care. Don't know if it's run-out, balance, airframe blocking or combination but it makes a big difference.

Thermos · #10 04-02-2010, 10:12 AM

I previously owned a share of a Piper Archer, we had problems with slight engine vibration we couldn't track down. Had the prop balanced, checked everything...until a sharp-eyed A&P mentioned that the prop had to be "clocked" correctly on the crankshaft. Following his advice, we removed and reinstalled the prop at the right position on the crankshaft...no more vibration. Unfortunately that was so long ago I can't remember where he got his information from.

So the engine may not care, but in our case changing the prop's position on the crankshaft solved our vibration issue. And less vibration should be a good thing...