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Old 06-30-2020, 05:14 PM
ultimate10201 ultimate10201 is offline
Join Date: Feb 2006
Location: McKinney, TX
Posts: 26
Default Prop Cycle rpm has changed

The rpm at which my Hartzell prop cycles during runup has recently changed. It used to always cycle easily at 1600 rpmís, 1400 rpmís, or even lower. I always wait until oil temp is approx. 100F before cycling the prop.

Governor is M/T which I bought in April 2006 (when they were still called Jihostroj by Vanís). Engine is IO360-A1B, 200 hp angle valve. The airplane was first flown in 2013 and has over 280 hours on it, now.

I originally had a single 7 cell oil cooler mounted behind #4. In July 2019, around 220 hours, I added another 6 cell cooler behind #3 to improve oil cooling (which works very well).

I had always run Shell 100W Plus and a pint of camguard at oil change. Engine has chrome cylinders so uses oil at a higher rate than steel cylinders. However, after installing the additional oil cooler, I started using Philips 20W50, no camguard. Oil consumption became a little less. Oil was added as needed, around Ĺ quart at a time.

I flew nearly 40 hours (with one oil change, Philips 20W50, at 25 hours) before the rpm change occurred.

At about 260 hours, unexpectedly, the prop wouldnít cycle until runup to about 2000 rpm.

It still works as expected in flight, maintaining rpm as before.

Iím aware recommended but not required 72 months recommended TBO.

But still, the change was sudden.

Could the Philips reduced oil viscosity (at the ≈ 100į runup temp) cause this? More total volume of oil due to the added cooler?

Any ideas welcome.
Daryle L. Grounds
McKinney, TX Based @ T31
RV-7, N33DG, IO-360-A1B, Hartzell C/S, Flying since 12/15/12; Swick TCraft under construction
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Old 06-30-2020, 08:34 PM
BillL BillL is offline
Join Date: Sep 2007
Location: Central IL
Posts: 5,373

The prop changes pitch by pressure and the pressure at 1600-1700 rpm is not that high. So, if it suddenly dropped off, then either the oil pressure (it would be obvious from the engine gauge) is low coming to the governor or restricted in the gov. The gov internal pump has a pressure relief and increases the pressure for moving the prop when loaded. (torque)

You might want to check the governor screen to see if it is restricted, if not, then something inside the gov sounds like it is not right.

The classic is to check the leak of the collar and bearing, but Allen Barrett told me he almost never had seen one fail. And that failure mode would not be sudden. A broken pressure relief spring would though (for instance).

Good luck!

Painted 6.11.2020
No Photo on my post? => PM me.

Last edited by BillL : 06-30-2020 at 08:37 PM.
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Old 06-30-2020, 09:00 PM
Taltruda Taltruda is offline
Join Date: Oct 2017
Location: Las Vegas, NV
Posts: 293

Just so you know, the Aeroshell 100wPLUS already has the Lycoming additive in it. So adding camguard probably isnít recommended. As for the Phillips XC20-50, that doesnít have the Lycoming additive, and could benefit from adding the additive (or camguard). I believe the Phillips Victory series of oils have the additive, so perhaps you should use that.
Las Vegas
RV-8 empenage started..
Horizontal Stab done! 2-15-2020
Vertical Stab Done! 5-27-2020
Rudder Done! 5-31-2020
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