Saratoga RPM fluctuations after prop overhaul?

jdfrey1

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Grand Rapids, MI
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Jeff Frey
I own a 1981 PA32R-301T Saratoga with a TIO-540 engine and 3-blade prop. I recently had a full engine teardown and prop overhaul after a line guy backed a tug into my prop at my local field. Thankfully the FBO has taken full accountability and the prop and engine were both sent out for inspection. The prop was overhauled and no major issues were found. The engine was also sent to Signature who did the last overhaul and they did a full teardown inspection and didn't find anything major. The engine only has about 300 hours SMOH and was not overhauled as part of this incident.

Now that the engine is put back together I am seeing RPM fluctuations of about +/- 15RPM at cruise power. I see this in slight variations on the mechanical tach but also on my JPI. I've attached a zip file that contains 2 JPI files. The flight just prior to teardown is Flight #280 and when I look at cruise RPM at 2400 I see very little variation. 2-3 RPM max and very stable. Flight #290 was this past weekend and I'm seeing the much larger variation of 2385-2415. The JPI is only 6 second interval sampling but the actual variation is constant. I don't really feel or hear any variations in power but because the mechanical tach is varying I don't believe the readings are erroneous.

I spoke to my shop about this and they checked with the prop shop and they are telling me that this could be a break-in symptom since the prop has been overhauled and how they setup the prop governor tightness. They don't seem to be worried and told me to keep an eye on it. I have about 4 hours since the prop overhaul and teardown. I'm just wondering if anyone has any thoughts on this and if I should be concerned?
 

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  • JPI Data.zip
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I've flown a few more hours and I'm still seeing the RPM fluctuation. I'm not comfortable with this so I wanted to get feedback on the video linked below. You can see that the JPI is showing about a +/-20 RPM variation and the mechanical tach is also varying as well. Any additional thoughts/recommendations?

https://youtu.be/1v6uogDd5-g
 
The best prop shop in the east that I know of is Sensenich at LNS. Only a little over an hour from you. Might be worth giving them a call for ideas.
 
A couple of things could be going on here.
First, I'd suggest seeing if there is any "slop" in the push-pull cable for your governor control. You can probably just put the prop control where it would be in cruise flight, then open the cowl and see if the control arm of the governor will move a little bit when you push on it with your fingers.

Secondly - although you didn't say that anything was done to your governor, the speeder spring in your governor may be getting weak.

Thirdly - I'm assuming you have a Hartzell prop - the blade preloads may be a little on the tight side. This can cause the prop to hunt.
 
I've flown a few more hours and I'm still seeing the RPM fluctuation. I'm not comfortable with this so I wanted to get feedback on the video linked below. You can see that the JPI is showing about a +/-20 RPM variation and the mechanical tach is also varying as well. Any additional thoughts/recommendations?

https://youtu.be/1v6uogDd5-g

Unfortunately I can't hear the engine. Do you have the Siamese magneto? When the coil starts going bad on those, the same symptom occurs.
 
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