O-470R power settings - Backcountry Pilot (2024)

Bringing up an old thread here.

I've got my O-470R in my 182 that I can't seem to get to run smooth in cruise. Up high 8-10k I run 2250 to 2300 RPM and and whatever manifold pressure I can get. Down low I will typically run 2100 to 2200 RPM and either 22 or 23 inches so that I can be square or over square. I also have an older 6 probe egt/cht that I use to assist in leaning.

I never seem to be able to get a power combination that runs smooth continuously high or low. I've tried adding a little carb heat and that doesn't seem to make much of a difference. When I say not smooth, it's not like too lean kind of rough, but it is not smooth.

I have about 250 hours on this engine since overhaul. I seem to remember that I didn't have this condition before overhaul.

Anyone have an O-470 that runs not as good at some power combinations and much better at others? Is there something else that I should be looking at?

soggyc wrote:Bringing up an old thread here.

I've got my O-470R in my 182 that I can't seem to get to run smooth in cruise. Up high 8-10k I run 2250 to 2300 RPM and and whatever manifold pressure I can get. Down low I will typically run 2100 to 2200 RPM and either 22 or 23 inches so that I can be square or over square. I also have an older 6 probe egt/cht that I use to assist in leaning.

I never seem to be able to get a power combination that runs smooth continuously high or low. I've tried adding a little carb heat and that doesn't seem to make much of a difference. When I say not smooth, it's not like too lean kind of rough, but it is not smooth.

I have about 250 hours on this engine since overhaul. I seem to remember that I didn't have this condition before overhaul.

Anyone have an O-470 that runs not as good at some power combinations and much better at others? Is there something else that I should be looking at?

Did you do any work to the prop at the engine O/H?

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The prop is a McCauley 2A34C66-N., and I didn't have anything done to it at overhaul. Maybe that was a mistake.

EGT values are fairly close to each other at cruise but #1 CHT is usually 100-150 degrees cooler than the rest.

I recognize that a prop that hasn't been balanced for a while will have more vibration than a freshly balanced one so I'm working to get it balanced. However, would an out of balance prop cause the engine to feel like its running a little rough? At takeoff and climb settings where I'm much more rich I don't notice this behavior.

The suggestion about plugs is a good one. The plugs were all new at overhaul time, but I guess that doesn't mean they are good. Is there anything specific is should be looking at for a diagnosis?

I was originally thinking plugs, mags or carb, but I I'm not sure if my symptoms point to one more than the other. I'll try and go and take some data at different power settings the next time I'm out and report back.

When cruising, have to tried to run higher RPM like 2400 or 2500? Does it still stay rough?

On leaning, what do you lean to? 100 ROP, 50 ROP, Peak, LOP? Does leaning procedure change the roughness?

Also, on it being smoother on takeoff and climb due to possibly richness...may be. But maybe not. I'm assuming you are also at higher RPM on take off and climb. My experience is that vibrations due to prop as well as vacuum leaks and ignition can be masked by higher RPM. Just food for thought.

Did you replace the engine mount rubbers at overhaul time? Old, stiff, or saggy rubbers might be (part of) the problem.
I had a little vibration thing going on with my C180 last year- almost not really noticeable, just not quite smooth.
Then during my usual look at everything at oil change time I discovered a crack in one of the tubes on the engine mount itself.
In between a new mount (thanks Clipwagon!) and new rubbers, it's back to being smooth.

I'm assuming mags were OH'd also? If not, maybe it's time.
I would try an in-flight mag check- does it run rougher on one than the other?
I would also resistance check my plugs-- should be 1200 ohms or less through a new plug, 5000 ohms means it's time to replace.

http://www.aircraftmagnetoservice.net/m ... ting-guide

I would also try removing the prop & re indexing it 180 degrees off.
If any this smooths things out, great.
If not, you might try having the prop dynamically balanced.
If your Granite Falls is the one in Washington, be advised that Tailspin Tommys at Jefferson County 0S9 does prop balancing.
And since the less expensive DynaVibe equipment came out, lots of others do prop balancing also.

Interesting that #1 is running cooler CHTs, usually that's the hottest cylinder in my experience. Are the EGTs fairly even or does #1 vary from the others as well?

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FWIW, in olden times before anyone had multipoint CHTs and EGTs and engine analyzers, the easiest way to get an O-470 to run smoother was to crank up the rpm to 2400 and leave it there. It worked.

Cary