Engine vibration

SixPapaCharlie

SixPapaCharlie

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Over the last few months, I have noticed a vibration that I don't recall being there before.
No changes have been made to anything.

I am scheduled for a prop balance next week but the MX said "3 blade prop on the Lycoming 540 sometimes vibrates and you might not be able to get rid of it."
Seemed like a weird thing to throw out but this is a mechanic that I trust and probably has balanced a lot of your props.

1. Is that true?
2. It seems to get progressively worse as I lower the RPM in cruise. I tend to run around 2400 and it is there but if I get down to 2300, 2200, the ipad shakes and my teeth rattle just a little. Would an out of balance prop vibrate more with the pitch adjustment?

Thanks.
 
Now that you mention it, I think I saw someone lurking near your hangar installing these on random airplanes…

69CC5C90-A0CE-4D43-8C42-EDDE70E73ABD.jpeg
 
I noticed when the paint wore off my prop it was not as balanced as before.
But this is not what you are experiencing I don't think?
I also can tell when my plugs are getting dirty by engine vibration. Or if you got a valve or rings not sealing up as good as before.
Good luck with it and let us know what you find.
 
SixPapaCharlie said:
Over the last few months, I have noticed a vibration that I don't recall being there before.
Click to expand...
SixPapaCharlie said:
my teeth rattle
Click to expand...
Since it is a noticeable change, the 1st thing you should do before flying again is pull the cowling and spend some time looking and grabbing for something loose. Be sure to check everything: prop spinner/plate, exhaust, engine mounts, etc. Don't just give it a once over. Have found and fixed more odd vibrations during this process than just rebalancing the prop.
SixPapaCharlie said:
. Is that true?
Click to expand...
In general, no, in my experience. But I have years of balancing experience which most fixed wing guys don't. Any vibration can be dealt with provided the component or part is serviceable, i.e., not falling apart. There are other items that can cause vibrations or cause you to feel them more in the cockpit. The prop is just the most obvious. Perhaps once your mechanic checks the prop, ask him to perform a spectrum analysis on the engine and look for out of spec vibs. A good spectrum can even determine if all the cylinders are firing equally. Good luck.
 
SixPapaCharlie said:
Over the last few months, I have noticed a vibration that I don't recall being there before.
No changes have been made to anything.

I am scheduled for a prop balance next week but the MX said "3 blade prop on the Lycoming 540 sometimes vibrates and you might not be able to get rid of it."
Seemed like a weird thing to throw out but this is a mechanic that I trust and probably has balanced a lot of your props.

1. Is that true?
2. It seems to get progressively worse as I lower the RPM in cruise. I tend to run around 2400 and it is there but if I get down to 2300, 2200, the ipad shakes and my teeth rattle just a little. Would an out of balance prop vibrate more with the pitch adjustment?

Thanks.
Click to expand...

I have the same O-540 and McCauley 3blade set up in my Comanche. Some days she likes 23/23 to be smooth, some days she likes 24/23 to be smooth. The shimmy and shake is a known issue with the McCauley 3 blade on Comanches. Some have found relief by changing the Lord motor mounts and getting a prop balance. Some that have done that didn't see any difference after spending the money.
 
I have a Hartzell 3 blade O-540 too. Mine has been balanced and it definitely has a sweet spot around 24" and 2300 or so rpm where vibration is minimized, but it's never as smooth as a 2 blade Balancing is a good idea, but imho it's not quite as effective as it is on a 2 blade. The other thing that can fool you into thinking the engine is vibrating excessively is the airflow from the prop buffeting the right wing root. A friend installed wing root fairings on his Comanche with a 3 blade and it was remarkable how much smoother it felt in the cabin.
 
are there MP/RPM restrictions on this prop?
 
I have the wing root fairings. I don't know a lot about my prop. I have the one with the extra bits on the trailing designed to make people ask "What's that for"?
I believe it is for cooling when used in conjunction with a cowl that I do not posess.


p.jpg
 
SixPapaCharlie said:
I have the wing root fairings. I don't know a lot about my prop. I have the one with the extra bits on the trailing designed to make people ask "What's that for"?
I believe it is for cooling when used in conjunction with a cowl that I do not posess.
View attachment 114964
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That's a different prop than I have. The hartzell page shows what I thought that prop was only for the 260's and not 250? https://hartzellprop.com/products/top-prop/piper/comanche-260-260b/ Hartzell doesn't show an applicable prop for 250 Comanches... https://hartzellprop.com/products/top-prop/piper/

Were your engine counterweights changed and governor upgraded to the higher RPM for 260hp?
 
Those are question generators…

Cracking myself right up! Ha!
 
You might also check the rest of the airframe for anything loose. I had a vibration I swore was related to engine rpm. I also had an aileron hinge that was a bit loose, that I could see vibrating in flight, which I thought was a symptom of the engine vibration. We tightened up that hinge and all the vibration went away. I assume there was some sort of harmonic that made the aileron vibrate at certain engine rpm's, which then shook the whole plane.
 
You should come over to my airport and meet Paul Williamson, a mechanic and hangar neighbor who flies the Comanche 260. He would be a treasure trove of valuable info..
 
Jay Urish said:
You should come over to my airport and meet Paul Williamson, a mechanic and hangar neighbor who flies the Comanche 260. He would be a treasure trove of valuable info..
Click to expand...

I may have to take you up on that. Maybe I can take him up and let him see what I am experiencing.
 
Don't forget the valves. We had vibration issues that our own mechanic didn't know much about, went to a large shop and they spent 2 days checking the valves and nothing. We thought maybe do the prop balancing will minimize it, ran around looking for someone to do it as big shop kept pushing us off. That's when we found our new engine guy who came to us ground ran it and said you have valve problems. Turns out when the last owner had new jugs put on they never did set the valve train right, and after 3 new right length push rod the vibrations are minimized and idle went from didn't know that was rough to butter smooth.
 
SixPapaCharlie said:
I have the wing root fairings. I don't know a lot about my prop. I have the one with the extra bits on the trailing designed to make people ask "What's that for"?
I believe it is for cooling when used in conjunction with a cowl that I do not posess.


View attachment 114964
Click to expand...

I have that prop. It's a Hartzell HC3 YK no AD prop. Rated to 2700 RPM if you have the LoPresti counterweight STC, otherwise it's limited to 2575 redline. The little paddles are called "synchro pulse" paddles and were supposed to force more air into the engine intake a and cooling ports of the high-performance LoPresti cowl. Note how the paddles line up with the cowl. Does it work? Meh...if everything Lopresti says added 5 knots did, I'd have a 300 knot airplane.
 

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I did notice in your photo a pretty large gap between your spinner backplate and cowl arch. Perhaps your motor mounts are getting a bit tired? Note mine is a lot tighter, as are most that I've seen, even on stock cowls.
 
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