Identifying the Source of a Vibration

[Marauder]

Over the past month I have noticed an increase in vibration in my plane. I just uploaded the recent flights to Savvy to see if they notice anything unusual. I did have the mag harnesses and plugs replaced shortly before I noticed the issue. One of the mags was adjusted for timing at that time.

Having owned the same plane for 26 years, I know something has changed and the plane now has a vibration I have never seen before. I am not seeing any decrease in speed, power or anything obviously different. MP, RPM, FF, CHTs, EGTs all look the same.

When I am slowed down for approaches, the vibration is less (almost unnoticeable) and it increases when I add full power for take-off and it is certainly noted in cruise.

My prop hasn't been dynamically balanced for a few years. I did note that my lower cowl enclosure had a nick on it most likely from the spinner making contact. Could this be an engine mount going bad?

Looking for ideas before I schedule service.

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[KSMooniac]

You might see if anyone near you has a Dyna Vibe kit...it can be used for dynamic balance, but also to isolate vibration sources by showing if they are 1:1 with RPM, or some other multiplier, or completely random.

I'd certainly check cowling, baffling, baffle seals, etc for any other signs of contact. Ditto for loose gear doors, cowl flaps, etc.

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[smwash02]

I've had a similar 'spider sense' go off and found the following in separate incidents.

• Induction leak from a deteriorating gasket (but your JPI data would show this)
• Engine Mounts sagging
• Exhaust hangar snapped
• Cowl flap movement from wear at the hinge point

[larryb]

New engine mounts made a big difference in vibration in my plane.

[gsxrpilot]

30 minutes ago, larryb said:

New engine mounts made a big difference in vibration in my plane.

Can you say approximately what the cost was for changing the mounts? Parts + Labor?  Or was it just part of the annual?

[N6758N]

2 hours ago, Marauder said:

 

Over the past month I have noticed an increase in vibration in my plane. I just uploaded the recent flights to Savvy to see if they notice anything unusual. I did have the mag harnesses and plugs replaced shortly before I noticed the issue. One of the mags was adjusted for timing at that time.

Having owned the same plane for 26 years, I know something has changed and the plane now has a vibration I have never seen before. I am not seeing any decrease in speed, power or anything obviously different. MP, RPM, FF, CHTs, EGTs all look the same.

When I am slowed down for approaches, the vibration is less (almost unnoticeable) and it increases when I add full power for take-off and it is certainly noted in cruise.

My prop hasn't been dynamically balanced for a few years. I did note that my lower cowl enclosure had a nick on it most likely from the spinner making contact. Could this be an engine mount going bad?

Looking for ideas before I schedule service.

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Chris,

I have a buddy who owns a shop just east of State College and has the Dynavibe kit, he does several balance jobs a week. I had him do my plane and it made a noticeable difference.  If you're interested we could take it up there and have him take a look. He doesn't charge much and he could take a good look at the mounts while he's at it. 

[larryb]

23 minutes ago, gsxrpilot said:

Can you say approximately what the cost was for changing the mounts? Parts + Labor?  Or was it just part of the annual?

It was 3.3 hours labor and $733 in parts. So around $1050.

[smwash02]

7 minutes ago, larryb said:

It was 3.3 hours labor and $733 in parts. So around $1050.

Depending which mounts you use, this is a good estimate. My C uses J-7402-1 which are "only" ~$110 each.

Your K needs 3x J-9613-75 at  $387 each and 1x J-9613-76 at $484....ouch.

 

[Yetti]

is it a clank clank  or the wiskey compass vibrates more?

[N201MKTurbo]

You might check that nothing in the engine compartment is hitting the cowl. The mounts can sag which is progressive, then all of a sudden it sags to where something starts banging on the cowl. It will make a big vibration.

[larryb]

Just now, N201MKTurbo said:

You might check that nothing in the engine compartment is hitting the cowl. The mounts can sag which is progressive, then all of a sudden it sags to where something starts banging on the cowl. It will make a big vibration.

Yes, that is one reason I changed my mounts. I found that the exhaust was hitting the firewall. I would feel and hear this under low power operation. Then I found that one of the mounts was quite soft and asked the shop to change them all at annual. The mounts were 11 years old at the time.

I was talking with the mechanic that did the work. He mentioned another airplane with a vibration. They went through all the usual suspects like plugs/wires/mags/fuel and finally the engine mounts. It was the mounts. I have a feeling the rubber mounts are an often-neglected item because the deterioration is so gradual, and some of the deterioration can be compensated for by shimming.

[bonal]

You might look at some photos if you have them of your spinner and cowling from years past and take a shot of todays position. I noticed my spacing top of spinner to cowl was less after all new lords were installed. no one is going to notice a not right feel better than you so something not right. My CFI and A&P have commented that my C is very smooth and it seems like to me but would be great for fly around in others for comparison

[Marauder]

Chris,
I have a buddy who owns a shop just east of State College and has the Dynavibe kit, he does several balance jobs a week. I had him do my plane and it made a noticeable difference.  If you're interested we could take it up there and have him take a look. He doesn't charge much and he could take a good look at the mounts while he's at it. 

Hey Terry. I would appreciate if you could look into it. Something isn't right, but I can't tell what is causing it.


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[Marauder]

is it a clank clank  or the wiskey compass vibrates more?

It is more sexual in nature. There is a nice seat vibration going on. In fact, I want to fly more often because of it.

Aside of the seat vibration, it is noticeable through the yoke a bit and if you have flown a plane a while, the ambient sound is off.

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[Browncbr1]

I recall in the maintenance manual that there is a spec for how far the starter motor bendix should be from the lower lip of the cowl.  I think it was something like 1" ... I know you have a cowl closure mod, but might be worth just checking that visually if you're able... it might provide clue regarding the motor mounts.

 

I'm sure you've already cleaned plugs,,etc. 

[Marauder]

You might check that nothing in the engine compartment is hitting the cowl. The mounts can sag which is progressive, then all of a sudden it sags to where something starts banging on the cowl. It will make a big vibration.

Rich -- that is one thing I am concerned with. The nick on the lower cowl enclosure is fairly recent. So it may be very well an engine mount. Can you tell by looking at a mount that something is amiss?


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[N201MKTurbo]

55 minutes ago, Marauder said:

 

 

Rich -- that is one thing I am concerned with. The nick on the lower cowl enclosure is fairly recent. So it may be very well an engine mount. Can you tell by looking at a mount that something is amiss?


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Not that I'm aware of. The lower ones will be a little squished looking in the front and the top will be squished in the back. If you wanted to go CB you could just shim them up some or rotate them. If you are going to go to all that trouble you should just replace them.

Rich...

[bonal]

Ok 26 you got this comming. perhaps you were flying solo and did not have one of your huge female vibration dampers on board.

[N6758N]

You can usually tell by looking at them if they are shot. They tend to sag in the direction of gravity usually on the firewall side, particularly on the bottom ones where there is more weight. Also don't rule out the bolts being loose, I have seen that more than once...

[Yetti]

3 hours ago, Marauder said:

It is more sexual in nature. There is a nice seat vibration going on. In fact, I want to fly more often because of it.

Aside of the seat vibration, it is noticeable through the yoke a bit and if you have flown a plane a while, the ambient sound is off.

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So it is rotational in nature.  Things that come to mind.   Alternator bearings and belt.  prop and spinner screws.  Engine.

[bradp]

Is it time to go through and star wiggling accessories?

I have had vibrations from broken stuff hanging in the wind cause vibration. Exhaust hangar in one instance, another my cowl flap hinge busted off. Those are just anecdotal.

My most common source of vibration in the cabin is my glareshield rattling on its frame. But this is only apparent at certain RPM setting

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[carusoam]

Large Marjey Dashpot called and said...

Some things generate vibrations...

Some things absorb vibrations. (A dashpot is one of those things if talking shock absorber technology)

Some things are naturally vibration indicators...

A broken engine mount sags the most...  you can get a lot of vibration from that....

The whiskey compass was a really good indicator as the little bubbles inside were moving all around.

loosening the mount on the compass calms the vibrations, but doesn't fix the problem...

PP things I learned about flying a completely warn in M20C...

Best regards,

-a-

Edited January 24, 2017 by carusoam

[smwash02]

6 hours ago, Marauder said:

 

Rich -- that is one thing I am concerned with. The nick on the lower cowl enclosure is fairly recent. So it may be very well an engine mount. Can you tell by looking at a mount that something is amiss?


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My spinner started scuffing my cowl enclosure too. I was floored how much extra clearance was gained when I replaced my mounts. You might even have to adjust shims depending when the enclosure was done.

[smwash02]

6 hours ago, Marauder said:

 

Rich -- that is one thing I am concerned with. The nick on the lower cowl enclosure is fairly recent. So it may be very well an engine mount. Can you tell by looking at a mount that something is amiss?


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Didn't see your question.

I've attached a picture of what they look like when they're shot. Wish I could find the side by side comparison I did, but alas it's gone. I also attached a photo of how they're supposed to look. Finally attached is what it looks like after a few hours. I'd only had my Mooney a couple months when I noticed and took action.

Alignment guide written by DMax.

 

[Marauder]

Didn't see your question.

I've attached a picture of what they look like when they're shot. Wish I could find the side by side comparison I did, but alas it's gone. I also attached a photo of how they're supposed to look. Finally attached is what it looks like after a few hours. I'd only had my Mooney a couple months when I noticed and took action.

Alignment guide written by DMax.

 

I have no where near that clearance. I can't even see the starter Bendix. Thanks for posting these.

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