Engine vibration

SixPapaCharlie

SixPapaCharlie

May the force be with you
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First Officer 6PC
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.
 
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.
 
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.
 
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...
 
Hello to all. I am having the same issue. Have always had a slight vibration at cruise (O-320 160hp, fixed pitch 2 blade newer Sensenich prop, run at about 2400rpm in cruise), and wanted to see it go. We rebalanced the prop and got the numbers down to 0.02. I believe that helped lower the vibration, but now at cruise, its back, and worse. Reduce to 2200, and its tolerable/minimal (but then so is airspeed reduction). Even running at 2300, and its still noticeable. At 2200, ya dont go anywhere real fast! I put a GoPro on the side and watched some pattern work and landings... nothing dragging or shaking. No nosewheel shimmy. Going to have my kid push down on the tail and then I will grab the nose gear and see if it moves at all. Other than that, next item might be a look at engine (Lord) mounts... altho engine is only out about 6-7 yrs from O/H. Re-index prop? It always stops at 11 and 5 (looking at nose).

Anyone else had success tracking this gremlin down? Thanks.
 
Glasair said:
Other than that, next item might be a look at engine (Lord) mounts... altho engine is only out about 6-7 yrs from O/H.
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Two questions:

1. Were the mounts replaced at overhaul? I have found old mounts on relatively recently-overhauled engines. False economy.

2. Are the mounts installed correctly? For example, the Dynafocal mounts use two different types on the same engine. One type is designed to take compression loads and they are installed on the top aft locations and bottom fronts. The others go in the opposing locations. Get them wrong, and funny stuff happens. In addition, some use an extra thick shim washer on the bottom fronts. The information that comes with the mounts has the details, but some folks don't read the instructions.
 
Unknown if the mounts were replaced at O/H. Gonna look at those next, once the midwest deep freeze loses its grip. Have to chuckle... had a clicking sound, thought maybe this was pushrod oriented... turns out 1 of 8 pushrods was slightly shorter. Amazing what you find after an "overhaul".

Reading on other sites about variations of prop dynamics/positioning. Some folks say vibration disappeared with re-indexing, and others say no. Some mentioned a ground-down camshaft being the culprit.
 
Glasair said:
Unknown if the mounts were replaced at O/H. Gonna look at those next, once the midwest deep freeze loses its grip. Have to chuckle... had a clicking sound, thought maybe this was pushrod oriented... turns out 1 of 8 pushrods was slightly shorter. Amazing what you find after an "overhaul".

Reading on other sites about variations of prop dynamics/positioning. Some folks say vibration disappeared with re-indexing, and others say no. Some mentioned a ground-down camshaft being the culprit.
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That's what we found too on our PA28. 2 rods were out of specs likely all the way from the last set of jugs. Guess dry tappet is not a thing for who ever did it.

Recently after some work we found roughness at idle. Turn out to be plugs. Cleaned both ends of each plug and everything is fine.
 
Glasair said:
We rebalanced the prop and got the numbers down to 0.02. I believe that helped lower the vibration, but now at cruise, its back, and worse.
Click to expand...
What RPM was the prop balanced at?

In reference to "but now at cruise, its back, and worse" how long after the prop balance did you notice this?

Did you or anybody perform any mx after the prop balance and before you felt the vib in flight?

Glasair said:
Reduce to 2200, and its tolerable/minimal (but then so is airspeed reduction).
Click to expand...
Are you sure it didnt reduce due to the lower airspeed?

Where do you feel the vibration? Control wheel? Seat frame? Rudder pedals?

Does it feel like a high frequency "buzz" or a low frequency "rumble"?

Glasair said:
Re-index prop?
Click to expand...
No. If you got it to .02 IPS then thats normally not the issue.
 
Bell206 said:
What RPM was the prop balanced at?

In reference to "but now at cruise, its back, and worse" how long after the prop balance did you notice this?

Did you or anybody perform any mx after the prop balance and before you felt the vib in flight?


Are you sure it didnt reduce due to the lower airspeed?

Where do you feel the vibration? Control wheel? Seat frame? Rudder pedals?

Does it feel like a high frequency "buzz" or a low frequency "rumble"?


No. If you got it to .02 IPS then thats normally not the issue.
Click to expand...
Balanced at 2400 rpm.
Hmmm... maybe 2-3 flights after the prop balance, I noticed the "Ruffles have Ridges" type of vibration, if you can make your tongue do the R... as best as i can explain it. Holding onto the frame, the seats, the stick.... very noticeable.
There was no maintainence after the balance.
It improves with lower RPM/hence lower airspeed at altitude.
 
Glasair said:
Hmmm... maybe 2-3 flights after the prop balance, I noticed the "Ruffles have Ridges" type of vibration, if you can make your tongue do the R... as best as i can explain it. Holding onto the frame, the seats, the stick.... very noticeable.
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The fact it was 3 flights after the prop balance and you can "feel" the frequency pulses for lack of a better term, it may point to something other than the prop as the vib source. Before you do anything else I'd recommend to index the spinner and remove it to make sure any prop balance weights have come loose. Then uncowl the engine and perform a visual and tactile check of all items in the engine compartment. Everything to include the engine mount itself.

Does the effect of the vibration, no matter how slight, noticed from engine start or does it become un-noticeable at some point or RPM?
 
Bell206 said:
The fact it was 3 flights after the prop balance and you can "feel" the frequency pulses for lack of a better term, it may point to something other than the prop as the vib source. Before you do anything else I'd recommend to index the spinner and remove it to make sure any prop balance weights have come loose. Then uncowl the engine and perform a visual and tactile check of all items in the engine compartment. Everything to include the engine mount itself.

Does the effect of the vibration, no matter how slight, noticed from engine start or does it become un-noticeable at some point or RPM?
Click to expand...
I will take off the spinner and check the balance weights... great idea... they COULD have come loose.

The vibration (of concern) is only between 2250 and full throttle. None at startup/taxi/runup/climbout/descent. Worse at 2400, which is where i want this engine running. Bringing the throttle back to 2200 in cruise is ok... but airpseed suffers.

Engine mounts next.

"Index the spinner"... do you mean to reverse it 180 degrees? Possibly the spinner itself? Hmmmm....
 
Glasair said:
Have to chuckle... had a clicking sound, thought maybe this was pushrod oriented... turns out 1 of 8 pushrods was slightly shorter. Amazing what you find after an "overhaul".
Click to expand...
Never heard of the dry tappet clearance check during cylinder replacement or engine overhaul? Mix those pushrods up, or put in a longer rod and you might be screwing things up enough to burn a valve. From the Lycoming direct-drive overhaul manual:

1739067188745.png
1739067210470.png
 
Glasair said:
"Index the spinner"... do you mean to reverse it 180 degrees? Possibly the spinner itself? Hmmmm....
Click to expand...
The guy who balanced your prop should have done this for you, but its important to ensure you reinstall the spinner back to its current "balanced" position. The prop is balanced with the spinner in this position and if you reclock the spinner you will throw off that balance.

Glasair said:
The vibration (of concern) is only between 2250 and full throttle.
Click to expand...
Vibrations can be funny and mask themselves. So unless you can positively discern between the vib of concern and any other vib you may want to ensure its only at 2250 and full throttle. Regardless, perform the visual check of the engine area for anything loose and see what you find.
 
The alternator's rotor is balanced at the factory. It turns at 10K RPM or so, so balance is critical. But if it's off a little, and the alternator mounting is a bit loose, you can get some strange vibrations as the alternator's imbalance resonates with any small engine imbalance as the phasing of the rotor and crankshaft constantly change.
 
Dan Thomas said:
The alternator's rotor is balanced at the factory. It turns at 10K RPM or so, so balance is critical. But if it's off a little, and the alternator mounting is a bit loose, you can get some strange vibrations as the alternator's imbalance resonates with any small engine imbalance as the phasing of the rotor and crankshaft constantly change.
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The alternator... didnt think to check that. Gotta take a good look at everything under the cowl and grab and see if anything moves. When I had my prebuy, the mechanic said everything 'looked good'. But when I got it home and did a close up and grabbed the exhaust on one side, it moved. The swivel ball joint was rusted and 'crunching'!

I didnt think of this earlier. We didnt have to remove the spinner for a prop balance, as washers are put on the flywheel... spinner doesnt have to be removed. But I did remove it some time ago... could've been me that put it on backwards.

This is an O-320 with a fixed pitch Sensenich.... not a constant speed. And the vibration is about 2350rpm to wide open throttle. 2200 and its barely there.
 
Glasair said:
This is an O-320 with a fixed pitch Sensenich.... not a constant speed. And the vibration is about 2350rpm to wide open throttle. 2200 and its barely there.
Click to expand...
Check the propeller track. That prop might be bent. Disconnect all the sparkplugs and take one out of each cylinder.
Chock both mains really firmly. Set a stool or bucket or whatever on the floor in front of the prop and place a stick so that the propeller tips pass really close to the end of the stick. Then rotate the prop and see if there is a difference in distance between each blade and the end of the stick. A bent or out-of-track prop can cause vibrations.
 
Without vibration velocity frequency information, forum diagnosis is very difficult. For any inventors out there - a handheld wand device is needed. 2350 rpm equals 38 Hz, but such a device should also look for 19 Hz and 76 Hz components
 
nrpetersen said:
a handheld wand device is needed.
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Or you can use balance equipment that can perform a vibration spectrum survey on the engine, then get a list of internal RPMs from the OEM and chase it that way. As for a wand, we would take an aluminum dowel rod and drill/tap one end to accept an accelerometer and start probing. Got the idea from Chadwick that offered a similar rod as an accessory to their older kits.
 
Another thing to look at is the timing of the different cylinders. If you have a carb especially, the power produced is inherently different between each cylinder.
This is a understandable artifact of different fuel flows to different cylinders. This is also especially seen more so at lower RPM's and "left of" the power curve (that is running leaner of peak). Injected makes that better, GAMI is said to solve that completely by balancing the fuel flow between all cylinders.

Is there something you can do on the ignition side? Timing, spark plug clean or re-gap, fuel line clean out?
Do you have an electric boost pump? Does anything change when you switch that on? And if you have a electronic engine monitor (EDM/JPI), can you validate the fuel flow vs RPM in a graph?

This is what I mean:
here you can see that the fuel flow is rather steady after the boost pump is off in cruise after take off and the fuel pressure remains stable with the fuel flow and RPM, if there are some fluctuations there, it could explain some of the vibrations you'd see if one cylinder on one side pushes harder against the crank then another on the other side...
xander
Screenshot 2025-02-16 at 1.52.40 PM.png
 
Does your spinner have a center-support on the inside to center it? If so it’s supposed to have some shims to make the hub have full contact with the inside of the spinner. Sometimes those gaskets can get compressed or lost/left out.
 
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