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Engine Balancing and Resonance Vibration Problem



 
 
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  #1  
Old September 4th 05, 10:12 PM
AllanFuller AllanFuller is offline
Junior Member
 
First recorded activity by AviationBanter: Sep 2005
Location: Nashua, NH and Benton, Maine connection
Posts: 6
Question Engine Balancing and Resonance Vibration Problem

Plane: Commander 114 - 1976 SN: 14007
Engine: Factor re manufactured - IO-540-T4A5D, tested 12/19/2000, SN: L-22326-48A, shipped end of 2000
Propeller: 3 bladed McCauley - just overhauled and balanced - July 2005

The current engine was put into service in March 2001 with the existing prop. There were engine vibrations and 13 washers were required to balance the prop as best as could be. I never felt it was as good and smooth as it should be considering it was a new engine.

This July 2005 (at the time of my annual) we had the prop overhauled at Memphis Prop at Memphis, Mississippi. They said they balanced the prop. It was installed and there was engine/prop vibration. There was also a resonance vibration that has a maximum at 1500 rpm and a second lower magnitude harmonic vibration at 750 rpm. I brought it to a nearby airport for dynamic engine/prop balance. The vibration at 2000 rpm was close to 1 without weights and they thought there was a problem with a bulkhead crack. We dye tested the bulkhead and there was no crack. We flipped the prop 180 degrees to see if that reduced the vibration. It did. This was actually the orientation of the prop when the prop was removed for the prop overhaul.

I brought the plane to another airport for engine balancing. They found that the vibration was about 0.9 without weights and they were able to bring the vibration down to about 0.12. Probably could have even improved on that, but the concern was that they needed about 13 washers. We flipped the prop 180 degrees and found that the vibration without weights was 1.4. Again the vibration could be lowered with the use of about 17 washers in the same direction on the bulkhead (same direction as the balancing of the new engine in 2001 with 13 washers). There still is this noticeable resonance vibration at 1500 and less intense resonance vibration at 750 rpm.

The difference in vibration with the two prop orientations is about 0.5. That probably suggests that the major vibration is in the engine and not static prop balance.

People have suggested that the vibration could be caused by a number of things. The Insight – GEM gauge show even CHT/EGT readings for all cylinders. The engine mounts were new at the time of the engine installation in 2001. The governor was overhauled in 2001 and yellow tagged. One observed problem is that prop cycling at 2000 rpm only produces a 250 rpm drop and one would expect least 300. Before the new engine and overhauled governor the engine rpm drop during prop cycling easily went to 300 and lower if I did not stop it by bring the prop forward. Currently, At 2300 rpm the prop cycling drop will go to 500 rpm. Is this an oil pump pressure or governor problem? Could this be the source of the vibration or the resonance vibration at 1500/750?

My problem is that I am not sure what to do. It is being suggested that I could replace the motor mounts at about $360 plus labor (They were new in 2001 and look good/new.). I could have the governor overhauled for $500 plus labor. I could have the prop sent back to the prop shop to check their work and re-balance. I will throw money at the problem, but I want to make smart choices on where to spend the time and money.

The other fear is that the vibrations are in the engine and related to the crank shaft recall. I certainly do not want the engine to fail when I am IMC or at night even if VFR. The resonance vibration coupled with the recall has me concerned. Having a doctorate in physics probably has me overly sensitized to the potential problem.

Thanks go to any and all who have comments and suggestions.

Allan Fuller
  #2  
Old September 5th 05, 01:49 AM
Jim Burns
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We had the props on our Aztec balanced this summer. The man that did it is
a long time friend of mine that runs an aerial application business (crop
dusting). He and his family have been in it all their lives they are all
CFIs A&P/Is. They own many airplanes and many helicopters. Anyway, they
know what they are talking about. They balance props on round engines, flat
engines, turbines, and blades on both shafts of the helicopters.

The biggest problem he told me that he's had balancing props/engines,
including round engines, is when the engine mounts are worn. Nothing you
do, no amount of weight, will balance a prop attached to an engine that has
bad mounts. Even if you don't think they look worn or burned, they can
loose their rigidity and become spongy. I replaced the mounts on our
right IO540 in less than 3 hours. Mounts from AirSuppliers.com cost me
$270.

Another thing to look for is to see if any weight had been added to the back
side of the ring gear/flywheel. You may be adding weight to the prop that
is counter-acting a weight that has already been added.

YMMV
Jim


  #3  
Old September 5th 05, 01:11 PM
AllanFuller AllanFuller is offline
Junior Member
 
First recorded activity by AviationBanter: Sep 2005
Location: Nashua, NH and Benton, Maine connection
Posts: 6
Default

Quote:
Originally Posted by Jim Burns
We had the props on our Aztec balanced this summer. The man that did it is
a long time friend of mine that runs an aerial application business (crop
dusting). He and his family have been in it all their lives they are all
CFIs A&P/Is. They own many airplanes and many helicopters. Anyway, they
know what they are talking about. They balance props on round engines, flat
engines, turbines, and blades on both shafts of the helicopters.

The biggest problem he told me that he's had balancing props/engines,
including round engines, is when the engine mounts are worn. Nothing you
do, no amount of weight, will balance a prop attached to an engine that has
bad mounts. Even if you don't think they look worn or burned, they can
loose their rigidity and become spongy. I replaced the mounts on our
right IO540 in less than 3 hours. Mounts from AirSuppliers.com cost me
$270.

Another thing to look for is to see if any weight had been added to the back
side of the ring gear/flywheel. You may be adding weight to the prop that
is counter-acting a weight that has already been added.

YMMV
Jim

Jim,

Thank you.

I did not see any weights on the ring gear, but I also did not make a point of looking closely. We thought it was symmetric and paid no attention to its orientation as we placed it on the engine and in the Bendix teeth. We will look more closely.

Replacing the mounts would insure that they are all the same with regards to stiffness and dampening effects. The current ones have about 600 hours on them. The io540 is a heavy engine cantilevered by 4 mounts. There could be some asymmetrical stiffness between the top and bottom mounts just from supporting that weight for 4 years. One of the mounts may have had difference physical properties when new. Seems like one of the things to do.

Are some mounts better than others? One would not expect the current ones to fail in 4 years and 600 hours. Picking the better quality mounts may be wise.

What about the 1500 rpm resonance vibration? Is any of this crank shaft related? The biggest concern is engine failure in flight. That can make for a bad day.

Allan
  #4  
Old September 5th 05, 09:26 PM
nrp
external usenet poster
 
Posts: n/a
Default

Possibly you might have both a small crankshaft flange runnout, and a
prop out-of-balance situation.

Your measurements are probably in inches per second (ips). If so.
reversing the prop should not give that much change in the optimum
vibration compensation vector. That makes the prop balance as rebuilt
suspicious.

Nevertheless, there is probably an inherent engine imbalance too, which
could come from a number of things besides just flange runnout.

You mentioned both a 750 RPM and a 1500 RPM rough spot. Is the
airframe responding at 12.5 Hz and 25 Hz - or is the response always at
the same frequency? I realize it may be hard to tell the difference.

It isn't the governor, and if the vibration came on suddenly on prop
rebuild - not related to the crankshaft recall.

  #5  
Old September 6th 05, 12:39 AM
external usenet poster
 
Posts: n/a
Default

On Sun, 4 Sep 2005 22:12:12 +0100, AllanFuller
wrote:

Below

snip

The current engine was put into service in March 2001 with the existing
prop. There were engine vibrations and 13 washers were required to
balance the prop as best as could be. I never felt it was as good and
smooth as it should be considering it was a new engine.


This would be your first clue. Was the propeller inspected at all at
this time? Flush and re-seal? If I needed "13 washers" to balance a
prop on a "new" engine, I would verify the propeller static balance at
a bare minimum. I'm betting that the prop was balanced, it was the
engine with an issue/issues.

This July 2005 (at the time of my annual) we had the prop overhauled at
Memphis Prop at Memphis, Mississippi. They said they balanced the prop.
It was installed and there was engine/prop vibration. There was also a
resonance vibration that has a maximum at 1500 rpm and a second lower
magnitude harmonic vibration at 750 rpm. I brought it to a nearby
airport for dynamic engine/prop balance. The vibration at 2000 rpm was
close to 1 without weights and they thought there was a problem with a
bulkhead crack. We dye tested the bulkhead and there was no crack. We
flipped the prop 180 degrees to see if that reduced the vibration. It
did. This was actually the orientation of the prop when the prop was
removed for the prop overhaul.


What was the IPS before and after the 180 degree "flip"? Again, if I
had overhauled the propeller, I would have removed it, re-verified the
static balance and blade angles. Still sounding like an engine problem
to me.

I brought the plane to another airport for engine balancing. They found
that the vibration was about 0.9 without weights and they were able to
bring the vibration down to about 0.12. Probably could have even
improved on that, but the concern was that they needed about 13
washers. We flipped the prop 180 degrees and found that the vibration
without weights was 1.4. Again the vibration could be lowered with the
use of about 17 washers in the same direction on the bulkhead (same
direction as the balancing of the new engine in 2001 with 13 washers).
There still is this noticeable resonance vibration at 1500 and less
intense resonance vibration at 750 rpm.


Third time, same story. Again, have the static balance and blade
angles on the propeller been verified? Are you aware that
manufacturers of prop dy-bal equipment forbid, repeat FORBID adding
weight/balancing an engine/prop combo that is over 1.0 IPS?

Again, I would guess that the prop is OK, but has it been verified?

The difference in vibration with the two prop orientations is about
0.5. That probably suggests that the major vibration is in the engine
and not static prop balance.


You've pretty much summed it up in one sentence.

People have suggested that the vibration could be caused by a number of
things. The Insight – GEM gauge show even CHT/EGT readings for all
cylinders. The engine mounts were new at the time of the engine
installation in 2001. The governor was overhauled in 2001 and yellow
tagged. One observed problem is that prop cycling at 2000 rpm only
produces a 250 rpm drop and one would expect least 300. Before the new
engine and overhauled governor the engine rpm drop during prop cycling
easily went to 300 and lower if I did not stop it by bring the prop
forward. Currently, At 2300 rpm the prop cycling drop will go to 500
rpm. Is this an oil pump pressure or governor problem? Could this be
the source of the vibration or the resonance vibration at 1500/750?


Find a picture, or do a little digging on the web/in the groups. I
know I've described the engine/governor/prop system at least a couple
of times over the years. On a single, the governor steps up the oil
pressure to "fatten" the pitch to control/reduce RPM. Low/no oil
pressure makes the prop go "flat".

If the engine/governor was not producing sufficient pressure, you
could not reduce engine RPM in flight using the prop control.
(emphasis on the period) Cycling the prop on the ground is a feel-good
crude ops check, not necessarily anything to be used for diagnosis.

My problem is that I am not sure what to do. It is being suggested that
I could replace the motor mounts at about $360 plus labor (They were new
in 2001 and look good/new.). I could have the governor overhauled for
$500 plus labor. I could have the prop sent back to the prop shop to
check their work and re-balance. I will throw money at the problem,
but I want to make smart choices on where to spend the time and money.


It sure sounds to me like you had the exact same problem when the
engine was initially hung/prop installed and the engine mounts
replaced w/new-unless I'm not reading things right. Getting the prop
condition verified is a no-brainer, it should have been done
immediately following the first dy-bal attempt after propeller o-haul.
If the governor is working at TO/cruise, I wouldn't worry about it.

The other fear is that the vibrations are in the engine and related to
the crank shaft recall. I certainly do not want the engine to fail when
I am IMC or at night even if VFR. The resonance vibration coupled with
the recall has me concerned. Having a doctorate in physics probably has
me overly sensitized to the potential problem.


I seriously doubt that the "crank shaft recall" is related to your
particular problem, but I do strongly suspect that your engine is the
source of your vibration.

Using your knowledge in physics (mine is strictly practical, sorry)
and my alleged experience in dy-bals, did any of the by-bal dudes
mount two transducers on your engine? Standard practice when faced
with a shaky weird engine/prop is to mount one 'ducer on the front of
the engine and one on the rear of the accessory case.

If the propeller imbalance is "making" the vibration, the rear 'ducer
should be picking up the vibration 180 degrees out of phase with the
front. The way a dynafocal engine mounting system is designed, in
theory (in a perfect world), the amplitude of the rear should be close
to the amplitude in the front.

Reducing the measured IPS on the front, should also reduce the IPS on
the back-are you following me? It was very, very, very rare, but I did
have a couple of engine/prop combos that I had to play with (trial and
error, coupled with experience) that I used an intentional imbalance
on the propeller/front (by adding too much weight in the "wrong" spot)
to reduce the IPS measured at the rear.

Again-strictly an assumption based on limited data and past
experience-I'm assuming that with the prop/front zero'ed out via
dy-bal you still have measurable vibration present at the engine/rear.

The only other concern that I have is that in another post, you
mentioned that you thought the ring gear support was uni-directional.
It should have no real bearing on what you are experiencing (unless it
has a stack of washers bolted to it), but it can only be installed
properly in one position.

regards;

TC

snip

  #6  
Old September 6th 05, 06:53 AM
John_F
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Posts: n/a
Default

There is ONE nut plate hole in the crankshaft flange that has a larger
diameter nut than the other bolt nut plates. If you index the prop
incorrectly the prop tip will NOT track correctly in a single plane
since the prop will not sit flush against the crankshaft flange. If
the prop does not track in a single plane then it will shake and it
will require a lot of weight to correct. A dial caliper will show
which crankshaft flange nut is the larger one and it should match up
with the larger hole in the prop. If someone has installed the prop
so that the larger nut is in the wrong prop hole then torqued the
bolts down it may look ok as the nut swages out the prop or the
extender spacer but is will not correctly seat and will wobble.

On Sun, 4 Sep 2005 22:12:12 +0100, AllanFuller
wrote:


Plane: Commander 114 - 1976 SN: 14007
Engine: Factor re manufactured - IO-540-T4A5D, tested 12/19/2000, SN:
L-22326-48A, shipped end of 2000
Propeller: 3 bladed McCauley - just overhauled and balanced - July 2005


The current engine was put into service in March 2001 with the existing
prop. There were engine vibrations and 13 washers were required to
balance the prop as best as could be. I never felt it was as good and
smooth as it should be considering it was a new engine.

This July 2005 (at the time of my annual) we had the prop overhauled at
Memphis Prop at Memphis, Mississippi. They said they balanced the prop.
It was installed and there was engine/prop vibration. There was also a
resonance vibration that has a maximum at 1500 rpm and a second lower
magnitude harmonic vibration at 750 rpm. I brought it to a nearby
airport for dynamic engine/prop balance. The vibration at 2000 rpm was
close to 1 without weights and they thought there was a problem with a
bulkhead crack. We dye tested the bulkhead and there was no crack. We
flipped the prop 180 degrees to see if that reduced the vibration. It
did. This was actually the orientation of the prop when the prop was
removed for the prop overhaul.

I brought the plane to another airport for engine balancing. They found
that the vibration was about 0.9 without weights and they were able to
bring the vibration down to about 0.12. Probably could have even
improved on that, but the concern was that they needed about 13
washers. We flipped the prop 180 degrees and found that the vibration
without weights was 1.4. Again the vibration could be lowered with the
use of about 17 washers in the same direction on the bulkhead (same
direction as the balancing of the new engine in 2001 with 13 washers).
There still is this noticeable resonance vibration at 1500 and less
intense resonance vibration at 750 rpm.

The difference in vibration with the two prop orientations is about
0.5. That probably suggests that the major vibration is in the engine
and not static prop balance.

People have suggested that the vibration could be caused by a number of
things. The Insight – GEM gauge show even CHT/EGT readings for all
cylinders. The engine mounts were new at the time of the engine
installation in 2001. The governor was overhauled in 2001 and yellow
tagged. One observed problem is that prop cycling at 2000 rpm only
produces a 250 rpm drop and one would expect least 300. Before the new
engine and overhauled governor the engine rpm drop during prop cycling
easily went to 300 and lower if I did not stop it by bring the prop
forward. Currently, At 2300 rpm the prop cycling drop will go to 500
rpm. Is this an oil pump pressure or governor problem? Could this be
the source of the vibration or the resonance vibration at 1500/750?

My problem is that I am not sure what to do. It is being suggested that
I could replace the motor mounts at about $360 plus labor (They were new
in 2001 and look good/new.). I could have the governor overhauled for
$500 plus labor. I could have the prop sent back to the prop shop to
check their work and re-balance. I will throw money at the problem,
but I want to make smart choices on where to spend the time and money.

The other fear is that the vibrations are in the engine and related to
the crank shaft recall. I certainly do not want the engine to fail when
I am IMC or at night even if VFR. The resonance vibration coupled with
the recall has me concerned. Having a doctorate in physics probably has
me overly sensitized to the potential problem.

Thanks go to any and all who have comments and suggestions.

Allan Fuller


  #7  
Old September 6th 05, 03:14 PM
Fly
external usenet poster
 
Posts: n/a
Default

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.








  #8  
Old September 6th 05, 09:43 PM
AllanFuller AllanFuller is offline
Junior Member
 
First recorded activity by AviationBanter: Sep 2005
Location: Nashua, NH and Benton, Maine connection
Posts: 6
Default

Quote:
Originally Posted by nrp
Possibly you might have both a small crankshaft flange runnout, and a
prop out-of-balance situation.

Your measurements are probably in inches per second (ips). If so.
reversing the prop should not give that much change in the optimum
vibration compensation vector. That makes the prop balance as rebuilt
suspicious.

Nevertheless, there is probably an inherent engine imbalance too, which
could come from a number of things besides just flange runnout.

You mentioned both a 750 RPM and a 1500 RPM rough spot. Is the
airframe responding at 12.5 Hz and 25 Hz - or is the response always at
the same frequency? I realize it may be hard to tell the difference.

It isn't the governor, and if the vibration came on suddenly on prop
rebuild - not related to the crankshaft recall.

nrp,

Thank you.

What is the significant of the 25 Hz and 12.5 Hz? There is a vibration that occurs when I reduce engine RPM's. When I approach 1500 RPM's there is a noticeable vibration that peaks at 1500 RPM’s and fall off. The vibration re-accrues at a much lower amplitude as the engine RPM pass through 750. I really do not know the frequency of this resonance vibration.

I talked to Memphis Propeller and I will be sending the prop with the bulk head to them to check static balance and if one of the blades is out of track or angled.

It is nice to rule out the governor.

I am going to try to address this is a logical way and try to through the possibilities quickly so that I can get the bird back in the air. I use it for business and flying is faster and more productive than driving to customer sites.

Allan
  #10  
Old September 6th 05, 10:18 PM
AllanFuller AllanFuller is offline
Junior Member
 
First recorded activity by AviationBanter: Sep 2005
Location: Nashua, NH and Benton, Maine connection
Posts: 6
Default

Quote:
Originally Posted by
On Sun, 4 Sep 2005 22:12:12 +0100, AllanFuller
wrote:

Below

snip

The current engine was put into service in March 2001 with the existing
prop. There were engine vibrations and 13 washers were required to
balance the prop as best as could be. I never felt it was as good and
smooth as it should be considering it was a new engine.


This would be your first clue. Was the propeller inspected at all at
this time? Flush and re-seal? If I needed "13 washers" to balance a
prop on a "new" engine, I would verify the propeller static balance at
a bare minimum. I'm betting that the prop was balanced, it was the
engine with an issue/issues.

This July 2005 (at the time of my annual) we had the prop overhauled at
Memphis Prop at Memphis, Mississippi. They said they balanced the prop.
It was installed and there was engine/prop vibration. There was also a
resonance vibration that has a maximum at 1500 rpm and a second lower
magnitude harmonic vibration at 750 rpm. I brought it to a nearby
airport for dynamic engine/prop balance. The vibration at 2000 rpm was
close to 1 without weights and they thought there was a problem with a
bulkhead crack. We dye tested the bulkhead and there was no crack. We
flipped the prop 180 degrees to see if that reduced the vibration. It
did. This was actually the orientation of the prop when the prop was
removed for the prop overhaul.


What was the IPS before and after the 180 degree "flip"? Again, if I
had overhauled the propeller, I would have removed it, re-verified the
static balance and blade angles. Still sounding like an engine problem
to me.

I brought the plane to another airport for engine balancing. They found
that the vibration was about 0.9 without weights and they were able to
bring the vibration down to about 0.12. Probably could have even
improved on that, but the concern was that they needed about 13
washers. We flipped the prop 180 degrees and found that the vibration
without weights was 1.4. Again the vibration could be lowered with the
use of about 17 washers in the same direction on the bulkhead (same
direction as the balancing of the new engine in 2001 with 13 washers).
There still is this noticeable resonance vibration at 1500 and less
intense resonance vibration at 750 rpm.


Third time, same story. Again, have the static balance and blade
angles on the propeller been verified? Are you aware that
manufacturers of prop dy-bal equipment forbid, repeat FORBID adding
weight/balancing an engine/prop combo that is over 1.0 IPS?

Again, I would guess that the prop is OK, but has it been verified?

The difference in vibration with the two prop orientations is about
0.5. That probably suggests that the major vibration is in the engine
and not static prop balance.


You've pretty much summed it up in one sentence.

People have suggested that the vibration could be caused by a number of
things. The Insight – GEM gauge show even CHT/EGT readings for all
cylinders. The engine mounts were new at the time of the engine
installation in 2001. The governor was overhauled in 2001 and yellow
tagged. One observed problem is that prop cycling at 2000 rpm only
produces a 250 rpm drop and one would expect least 300. Before the new
engine and overhauled governor the engine rpm drop during prop cycling
easily went to 300 and lower if I did not stop it by bring the prop
forward. Currently, At 2300 rpm the prop cycling drop will go to 500
rpm. Is this an oil pump pressure or governor problem? Could this be
the source of the vibration or the resonance vibration at 1500/750?


Find a picture, or do a little digging on the web/in the groups. I
know I've described the engine/governor/prop system at least a couple
of times over the years. On a single, the governor steps up the oil
pressure to "fatten" the pitch to control/reduce RPM. Low/no oil
pressure makes the prop go "flat".

If the engine/governor was not producing sufficient pressure, you
could not reduce engine RPM in flight using the prop control.
(emphasis on the period) Cycling the prop on the ground is a feel-good
crude ops check, not necessarily anything to be used for diagnosis.

My problem is that I am not sure what to do. It is being suggested that
I could replace the motor mounts at about $360 plus labor (They were new
in 2001 and look good/new.). I could have the governor overhauled for
$500 plus labor. I could have the prop sent back to the prop shop to
check their work and re-balance. I will throw money at the problem,
but I want to make smart choices on where to spend the time and money.


It sure sounds to me like you had the exact same problem when the
engine was initially hung/prop installed and the engine mounts
replaced w/new-unless I'm not reading things right. Getting the prop
condition verified is a no-brainer, it should have been done
immediately following the first dy-bal attempt after propeller o-haul.
If the governor is working at TO/cruise, I wouldn't worry about it.

The other fear is that the vibrations are in the engine and related to
the crank shaft recall. I certainly do not want the engine to fail when
I am IMC or at night even if VFR. The resonance vibration coupled with
the recall has me concerned. Having a doctorate in physics probably has
me overly sensitized to the potential problem.


I seriously doubt that the "crank shaft recall" is related to your
particular problem, but I do strongly suspect that your engine is the
source of your vibration.

Using your knowledge in physics (mine is strictly practical, sorry)
and my alleged experience in dy-bals, did any of the by-bal dudes
mount two transducers on your engine? Standard practice when faced
with a shaky weird engine/prop is to mount one 'ducer on the front of
the engine and one on the rear of the accessory case.

If the propeller imbalance is "making" the vibration, the rear 'ducer
should be picking up the vibration 180 degrees out of phase with the
front. The way a dynafocal engine mounting system is designed, in
theory (in a perfect world), the amplitude of the rear should be close
to the amplitude in the front.

Reducing the measured IPS on the front, should also reduce the IPS on
the back-are you following me? It was very, very, very rare, but I did
have a couple of engine/prop combos that I had to play with (trial and
error, coupled with experience) that I used an intentional imbalance
on the propeller/front (by adding too much weight in the "wrong" spot)
to reduce the IPS measured at the rear.

Again-strictly an assumption based on limited data and past
experience-I'm assuming that with the prop/front zero'ed out via
dy-bal you still have measurable vibration present at the engine/rear.

The only other concern that I have is that in another post, you
mentioned that you thought the ring gear support was uni-directional.
It should have no real bearing on what you are experiencing (unless it
has a stack of washers bolted to it), but it can only be installed
properly in one position.

regards;

TC

snip

TC,

Thank you and everyone on their comments.

I am going to have the prop checked to make sure it is not the problem. The process of using 2 sensors (or locations) for dynamic balance will be checked out. I probably should have been more proactive about addressing the problem when it was clear that a large amount of weight was required to balance the new engine.

I will check the ring gear weights and its position more carefully.

I will post the results of the check out of the prop by Memphis Propeller. They have been great and supportive.

I am not sure if I should change or rotate the mounts while I am waiting for the propeller to be checked out. Considering the time involved in getting to the mounts maybe new mounts are best. Is there a preferred supplier of mounts? Are all mounts of equal quality?

Changing too many things at a time may make assigning the source of the problem difficult.

I am not sure what to do if the vibrations are in the engine. I will cross that bridge after I hear from the prop shop.

Again thanks to all for their comments. I will post an update as soon as available. Hopefully I will be flying in two weeks.

Allan

Last edited by AllanFuller : September 6th 05 at 10:35 PM.
 




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