Engine Balancing and Resonance Vibration Problem

Originally Posted by Fly

I concur with ToeCutter.
Especially in your case, you need two vibration sensors, fore and aft, to
gather info on the engine and prop. You can surmise what the crankshaft
balnce quality is. You cannot do it with one sensor alone unless you move
the sensor to different locations during subsequent runs..

Your post stroungly suggests you need to get find someone of experience to
give you good advice.
I wonder where are you located?

Wish I could help with a good answer but internet makes it difficult.
Answer is only a good as the information provided.

couple of other things:

Sounds as if the operator has a Micorvibe DSS prop balancing rig.
Their manual suggest checking the balnce at 2000 rpm.
Usually I find higher amplitudes of imbalnce and sometimes different phase
at higher rpms.

The previous balance of 13 washers was beyond the FAA approved maximum
correction.

After 600 hours, the isolation mounts can take a set, maybe even have
metal-to metal contact between the bolt and engine mount.
I recall Toecutter suggesting at least a rotation every 500 hours.

Doublecheck the ring gear installation. It will only go on in one position.
And verify the crankshaft index bushing is in the correct location for your
engine.

How are you percieving the resonance at 1500? How did you measure the freq?
have you consider that it might be an idle mixture problem?

good luck

Kent Felkins
Tulsa Ok.

Reply below in quotes:

Originally Posted by Fly

I concur with ToeCutter.
Especially in your case, you need two vibration sensors, fore and aft, to
gather info on the engine and prop. You can surmise what the crankshaft
balnce quality is. You cannot do it with one sensor alone unless you move
the sensor to different locations during subsequent runs..

"Thank you for the suggestion. It is something to learn more about and try."

Your post stroungly suggests you need to get find someone of experience to
give you good advice.

"That is why I have posted this request for information. We are learning a lot through this process. The feedback is good and opens up a number of things to think about and try. There is a problem that probably was in the engine when it was new. The prop overhaul has either added to the problem or heightened the concern. One would think the engine/prop should be smooth as silk since the engine is relatively new and the prop has been just overhauled. I spend a lot of money keeping the plane in good repair. I have owned it since 1985. When it is not right, I know it quickly."

I wonder where are you located?

"Nashua, NH"

Wish I could help with a good answer but internet makes it difficult.
Answer is only a good as the information provided.

couple of other things:

Sounds as if the operator has a Micorvibe DSS prop balancing rig.
Their manual suggest checking the balnce at 2000 rpm.
Usually I find higher amplitudes of imbalnce and sometimes different phase
at higher rpms.

"It is a chadwick-helmuth spectrum analyzer."

The previous balance of 13 washers was beyond the FAA approved maximum
correction.

After 600 hours, the isolation mounts can take a set, maybe even have
metal-to metal contact between the bolt and engine mount.
I recall Toecutter suggesting at least a rotation every 500 hours.

Doublecheck the ring gear installation. It will only go on in one position.
And verify the crankshaft index bushing is in the correct location for your
engine.

"We Will double check the ring gear."

How are you percieving the resonance at 1500? How did you measure the freq?

"The vibration is by feel as the engine RPM is reduced from 2000 to idle slowly. The vibration increases as one slows to 1500, peaks at 1500 and decrease to normal engine vibration."

have you consider that it might be an idle mixture problem?

"No, net yet, but something to consider."

good luck

"Thank you. Next step is to double check the prop at the prop shop."

Kent Felkins
Tulsa Ok.