Backcountry Pilot • Prop won't cycle... at first

Prop won't cycle... at first

Lycoming, Continental, Hartzell, McCauley, or any broad spectrum drive system component used on multiple type.
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Prop won't cycle... at first

On run-up, when you pull the prop knob & listen for the prop to cycle, what would cause it not do do anything for several seconds? I usually give up and push it back in, then on the 2nd & 3rd pull, you can hear it cycle promptly as expected. Once it took 2 pulls of "nothing", then cycled normal on 3rd & 4th try.

Cold oil? I've tried longer warm up first with no joy.

182C / O470-L
NETX offline
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Re: Prop won't cycle... at first

Mine is similar. First pull I have to wait quite a bit for it to drop, then any subsequent pulls, and function throughout the flight is just fine. I figure either the oil in the prop is cold, or has "leaked down"??? I don't completely understand how the inside operates, so I don't know if the oil can drain back into the motor when it sits??
ebag offline
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Re: Prop won't cycle... at first

I've had the following explained to me regarding this, although I have not seen it myself.

One of the governor gaskets has a screen in it that filters the oil supply associated with the governor. If that screen gets dirty, it can slow the flow of oil in and out of the governor. It drains back into the pan slowly when you shut down, and then builds pressure slowly when you start up.

The particular engine in the described case took 10 seconds to get the prop to cycle the first time.
jcadwell offline
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Re: Prop won't cycle... at first

Possibilities I can think of are a dirty oil screen as jcadwell mentioned or a worn oil pump in the prop governor.

Pic of gasket/screen I pulled from google:
Image

A couple threads that may be of interest:

https://backcountrypilot.org/forum/inside-a-prop-governor-21064

...well, I can't seem to find the thread I thought I posted of the Mccauley prop hub I tore apart...maybe I didn't post it #-o
whee offline
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Re: Prop won't cycle... at first

You could also have sludge buildup in the prop hub, or the crankshaft hole leading to it. Oil doesn't circulate a whole lot in there and builds up this really gummy, thick stuff that you have to clean out manually. Fortunately it's not hard to clean the crank, but does require pulling the prop so your friendly local A&P should be involved. At minimum you'll be replacing the O-ring if you do that, so have that ahead of time. Anything deeper in the hub you can't easily access with a rag would be a much larger project. My A&P won't even touch prop hubs except to send them to a qualified shop nearby.
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Re: Prop won't cycle... at first

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Last edited by dogpilot on Thu Aug 06, 2020 12:44 am, edited 1 time in total.
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Re: Prop won't cycle... at first

Almost always, every CS prop that I've ever flown takes awhile for the prop to cycle when cold. I way "almost always", because the exception is with my current airplane if I've left the pre-heater on all night and the cowl, prop, and spinner covers in place, so that the oil in the hub is warm. But even on a nice warm day, the oil in the hub is cold if the engine wasn't pre-heated.

Just for instance, Wednesday afternoon, with temps in the mid-80s, I think I could have counted to 3 before the rpm changed when I pulled the prop knob.

If I haven't pre-heated and the temps are hovering around 40 F, it'll take longer. I've had it take long enough that I wondered if it was going to adjust, although it always has.

A few seconds is nothing to worry about.

Cary
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Re: Prop won't cycle... at first

This is great, thanks for the replies / info... enlightening as always.

Hopefully the rubber is good & there's no old sludge yet as this prop was "resealed" (as opposed to overhauled) just 15 hours ago. Well that was at the time of purchase... I suppose 25-30 hours ago now, although it was done sometime ago before the recent annual and sale.

I don't know the difference, but it looked new, so they must have at least repainted the blades at the same time, there was not even the slightest hint of paint wear on the tips or leading edges.

Sounds like I won't worry too much & just go flying!
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Re: Prop won't cycle... at first

Curious as to what model prop,
and if it's oil filled or grease filled.
I'm thinking grease-filled might be slower in cycling.
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Re: Prop won't cycle... at first

Hey I'm curious about that too! I'll see if I can find out when I get back to the logs.
I'm not familiar with "grease filled" I guess...
I've got a lot to learn about what I've got now that I've got it! It's going to be a fun journey.
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Prop won't cycle... at first

dogpilot wrote:Perhaps you are forgetting why we cycle the prop during run up in the first place. This is not a very magic system, in fact it is quite simple. The governor is just a metering valve that is controlled but some spinning weights to regulate RPM. The valve is a simple push pull affair. The prop dome is a big piston with a spring on one side. So oil pressure pushes on one side and the spring on the other. There is no regular circulation of oil going to and from the dome. At start it is full of cold oil. Cold oil makes the giant O ring in the dome less slippery, since it is a bit stiff. So almost every aircraft with a controllable pitch prop has you cycle the prop to circulate some warm oil into the dome so it responds quicker, like on takeoff.

The big O ringing the dome is one of those things that get stiff that are super nice to replace on the calendar schedule prop overhaul. It is all the rubber bits that decay at a predictable rate that have to be replaced. If your screen on the gasket has that much crud on it, you have bigger problems than just slow cycling.


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Re: Prop won't cycle... at first

Image

Ok, so I found out what my prop is... but it's all Greek to me. I'm guessing it's what all 182C's came out of the factory with?

Prop model is McCauley model #2A34C66-NP
Ser. #788195
Blade model 90AT-8
Blade serial #'s C10777YS & C10757YS

Does any of that mean anything to anyone? Shoot, why couldn't they have just put an MT on it from the get-go? Lol

Flew again yesterday, same thing.... 2 pulls with pause & wait of at least 5 seconds with nothing. 3rd & 4th pull got normal cycling response right away. Guess I won't worry about it unless something else changes.
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Re: Prop won't cycle... at first

What rpm are you cycling the prop at? We fixed that problem by increasing rpms to 2100 to cycle the prop at the guidance of our mechanic. I think it was in the POH too but I’ll have to check next time I’m out. I’m no mechanic but just a thought.

Good luck,

CW
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Re: Prop won't cycle... at first

Interesting, I'll try that. I've been doing it, as well as the rest of the run up, at 1700.
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