Post prop-overhaul oddities

[Timothy Quigley]

Just had the Hartzel two blade prop overhauled on my 260B. Also had the prop governor replaced with a PCU5000 as the old one was worn beyond some limits and a new one was the same price as part and cost of overhaul.

When we got the plane back, my partner reported two oddities that I was curious about:

1. On takeoff, the plane seems to go over max RPM by about 50 RPM. The mechanic says its likely the tachometer rather than the prop. I don't like working in the world of "likely". But, not knowing how the governor works, what process things go through at the prop shop calibrating such things, etc. I can't really form an opinion. Thoughts on this?

2. In the past our normal "run-up" procedure was to bring the engine to 1500 or 1700 RPM and cycle the prop and then go to 2000 RPM for the mag check. When my partner flew the plane, he says he got no response when cycling it at 1700. At 2000 it cycled fine. Does that make any sense at all?

I can wrap my head around item 1 and figure we can check it with an electronic RPM meter when we get the prop dynamically balanced. #2 just doesn't seem right at all. Just curious if someone here can add some perspective.

Thanks,
Tim
N9024P

[N3322G]

If it works like our Twin, sludge can accumulate in the chamber and needs to be cleaned out when the prop is removed.
If the gauge wasn't a problem before the overhaul, it shouldn't be a problem after the overhaul.
Was the governor overhauled at the same time? Was the governed or anything else adjusted during this maintenance work?

[Timothy Quigley]

The prop was overhauled and the governor was replaced with a new unit.

[LeWayne Garrison]

It sounds to me like both problems are with the governor adjustment. Basically the governor is just an oil pump that pumps oil into the prop to change the pitch of the blades. If the pump isn't adjusted correctly you might see what is happening.

[N3322G]

Once had both governors OHd by Hartzell. Left was perfect, right took 4 more iterations at Piqua to get it running as it should.

[Clarence Beintema]

Tim,

I would suspect that your tachometer is the issue, you will need some form of tachometer check to verify.

The cycling at higher RPM is a fuction of the governor, unless the installer left a rag on the crankshaft bore.

Clarence

[William Hughes]

You can chase a 50 rpm tach variation a long way. Mine reads right on when high and about 80 low when warm. Drove me nuts chasing it. Also, the constant speed part of props is not perfect. There is some natural variation as the oil warms up, attitude of the aircraft changes, amount of torque involved, and so on and so forth. Eventually I learned to accept that my tach was not now and never would read correctly to a narrow spec. Someday I will install a digital engine monitor and put that to rest.

I know that I get very sensitive to the aircraft after any major maintenance. I start asking myself, "Did it always make that noise? Did the rudder pedals always feel like that? Did the oil pressure always read that much?" Sort of like bush roughness.

The prop certainly should cycle at 1500. There should also be a lagging oil pressure rise as it works.

[Timothy Quigley]

[N3322G]

Good for you. On our Twin the dome pressure can also impact performance. If you download the Hartzell prop manual, it may also assist.