Wierd vibration -- Prop or engine, balance or not???

Hi guys & gals,

I purchased an older Cherokee 180 with a Lycoming O-360A4A and
Sensitech propeller. Unfortunately, I'm not sure on of the prop model
as I haven't pulled the cone yet.

Since I purchased my Cherokee, there has been a slight vibration in it
while running and flying. The first mechanic I had went for a ride
with me and immediately said the prop needed a "balance" job.

But since then, another very experienced A&P has told me that
fixed-pitch props are never "balanced". This guy told me that balance
jobs are done on constant-speed props and not fixed-pitch.

So, does anyone have experience with a balance job on a fixed-pitch
prop? Or has anyone had a vibration problem that turned out to be a
fixed-pitch prop balance problem???

I ask because it would take a week to get the equipment in and of
course, cost several hundred for the prop balance. I'd hate to spend
that money and still have the vibration problem.

Thanks for any suggestions or information you guys can offer.



Chuck
N7398W

Since I purchased my Cherokee, there has been a slight vibration in it
while running and flying. The first mechanic I had went for a ride
with me and immediately said the prop needed a "balance" job. BRBR

A prop shop can static balance the prop out of the plane and most can dynamic
balance it once it is installed.

Second mechanic isn't correct.

However, there are limits to the level of balance to be acheived.


--
Dr. Nuketopia
Sorry, no e-Mail.
Spam forgeries have resulted in thousands of faked bounces to my address.

On Sun, 28 Nov 2004 03:36:25 GMT, Chuck wrote:

Hi guys & gals,

I purchased an older Cherokee 180 with a Lycoming O-360A4A and
Sensitech propeller. Unfortunately, I'm not sure on of the prop model
as I haven't pulled the cone yet.

Since I purchased my Cherokee, there has been a slight vibration in it
while running and flying. The first mechanic I had went for a ride
with me and immediately said the prop needed a "balance" job.

But since then, another very experienced A&P has told me that
fixed-pitch props are never "balanced". This guy told me that balance
jobs are done on constant-speed props and not fixed-pitch.

So, does anyone have experience with a balance job on a fixed-pitch
prop? Or has anyone had a vibration problem that turned out to be a
fixed-pitch prop balance problem???

I ask because it would take a week to get the equipment in and of
course, cost several hundred for the prop balance. I'd hate to spend
that money and still have the vibration problem.

Thanks for any suggestions or information you guys can offer.

A dynamic prop balance would probably smooth the ride. Another thing
to check is the engine mount dampeners - if they are shot, no amount
of dynamic prop balancing will fix the vibration.

"Chuck" wrote:
But since then, another very experienced A&P has told me that
fixed-pitch props are never "balanced". This guy told me that balance
jobs are done on constant-speed props and not fixed-pitch.

Are you sure you understood him correctly? If so, you need to stay away
from this guy.

[snip]

I ask because it would take a week to get the equipment in and of
course, cost several hundred for the prop balance. I'd hate to spend
that money and still have the vibration problem.

Might happen, but the prop should be dynamically balanced, anyway. For
the money, it's one of the best things you can do for your airplane. An
out-of-balance prop can have all sorts of bad effects on the airframe,
engine, avionics, etc.
--
Dan
C172RG at BFM

On Sun, 28 Nov 2004 03:36:25 GMT, Chuck wrote:

Below, interspersed

Hi guys & gals,

I purchased an older Cherokee 180 with a Lycoming O-360A4A and
Sensitech propeller. Unfortunately, I'm not sure on of the prop model
as I haven't pulled the cone yet.

It's either a 76EM8 or a 76EM8S5

Since I purchased my Cherokee, there has been a slight vibration in it
while running and flying. The first mechanic I had went for a ride
with me and immediately said the prop needed a "balance" job.

But since then, another very experienced A&P has told me that
fixed-pitch props are never "balanced". This guy told me that balance
jobs are done on constant-speed props and not fixed-pitch.

So, does anyone have experience with a balance job on a fixed-pitch
prop? Or has anyone had a vibration problem that turned out to be a
fixed-pitch prop balance problem???

I've balanced quite a few of them. Honestly, if you have a vibration
problem, you should probably have the propeller removed and inspected
for condition/static balance by a prop shop.

I really don't want to be the one to tell you this, but anyone
purchasing any aircraft with this engine/prop combination should have
the prop inspected as part of the pre-buy inspection.

This engine/prop installation has zero tolerance for diameter
reduction. Unfortunately, it is quite common for the tips to be
re-worked and re-painted, if the prop has been "shortened" at all, it
is no longer airworthy.

I ask because it would take a week to get the equipment in and of
course, cost several hundred for the prop balance. I'd hate to spend
that money and still have the vibration problem.

When I was in the dy-bal business, we often charged a reduced rate if
no "balancing" was needed. Can't you find someone in your area that
performs dy-bals on a regular basis?

TC

snip

Your 2nd A&P doesn't know what he is talking about.
85% chance yours can be helped. I have the records to prove it. I
have checked over a thousand.

Find somebody in your area to check it. $175-225 probably.
Savy technician can give you opinion on whther lord mounts are bad.

Kent Felkins
Tulsa

"Chuck" wrote in message
...
Hi guys & gals,

I purchased an older Cherokee 180 with a Lycoming O-360A4A and
Sensitech propeller. Unfortunately, I'm not sure on of the prop model
as I haven't pulled the cone yet.

Since I purchased my Cherokee, there has been a slight vibration in it
while running and flying. The first mechanic I had went for a ride
with me and immediately said the prop needed a "balance" job.

But since then, another very experienced A&P has told me that
fixed-pitch props are never "balanced". This guy told me that balance
jobs are done on constant-speed props and not fixed-pitch.

So, does anyone have experience with a balance job on a fixed-pitch
prop? Or has anyone had a vibration problem that turned out to be a
fixed-pitch prop balance problem???

I ask because it would take a week to get the equipment in and of
course, cost several hundred for the prop balance. I'd hate to spend
that money and still have the vibration problem.

Thanks for any suggestions or information you guys can offer.



Chuck
N7398W

Balancing a prop dynamically is like getting the alignment done on
your car. You do it, only way to know if it was out, is if it is
better after you do it.
Anyway, just do it, it will probably help.

ode (nuke) wrote in message ...
Since I purchased my Cherokee, there has been a slight vibration in it
while running and flying. The first mechanic I had went for a ride
with me and immediately said the prop needed a "balance" job. BRBR

A prop shop can static balance the prop out of the plane and most can dynamic
balance it once it is installed.

Second mechanic isn't correct.

However, there are limits to the level of balance to be acheived.

Chuck wrote:

So, does anyone have experience with a balance job on a fixed-pitch
prop? Or has anyone had a vibration problem that turned out to be a
fixed-pitch prop balance problem???

I had a vibration problem with my old Cessna 150 that we couldn't track down.
I finally had the prop removed an sent out for inspection. Turned out that one
blade had a different pitch from the other. I think some amateur tried to turn
it into a cruise-pitch prop. A prop overhaul cured my problem.

In any case, there are shops out there that will balance fixed pitch props. A
dynamic balance job will make it run much more smoothly -- until the next time
someone files a nick out of the prop.

George Patterson

Chuck wrote:
: Hi guys & gals,

: I purchased an older Cherokee 180 with a Lycoming O-360A4A and
: Sensitech propeller. Unfortunately, I'm not sure on of the prop model
: as I haven't pulled the cone yet.

: Since I purchased my Cherokee, there has been a slight vibration in it
: while running and flying. The first mechanic I had went for a ride
: with me and immediately said the prop needed a "balance" job.

I've got the same plane/engine/prop combination. I had to change the
alternator belt a few months ago and my mechanic and I decided that the prop wasn't
indexed properly. The prop has a 6-bolt pattern so it could be put on incorrectly at
60 degree increments. The compression stroke used to put TDC with the prop at 3-9
o'clock. Now, it's more like 1-7 o-clock. It significantly reduced the vibration on
mine.

I know that the prop is supposed to be on only one way. The really annoying
thing is that the service manual for the plane says TDC should be at 2-8 o-clock....
exactly halfway between the two possible positions. My mechanic and I puzzled over it
for awhile, but eventually decided (from the way other Cherokees' had their props
indexed) that it should be moved. I can see why the previous owner may have put it on
the other way, but since the vibration is much reduced now I believe this way is
correct. I've also heard rumors about pigs flying and a slight manifold pressure
increase from having the carb air induction in the correct position to get a bit of
propwash. Not sure I buy it, but the new position would seem to make that more
possible (fiberglass clamshell cowling on mine).

Seems stupid to make it possible to put the prop on wrong, but they did.
Pity, too... it was much easier (and safer) to pull the prop through the compression
stroke at the 3-9 o'clock position.

-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

Chuck

In my life I've purchased two brand new fixed pitch props. The first
was a replacement for an overhauled O-300D and the second for my
present 1975 172M when it was new. Both were made by McCauley, both
were out of balance when new, and both were made to run smooth by
Kenny Maxwell (a local prop shop).

I don't know how he does it given the comparatively crude tools used,
but he did. They were not balanced on the engine afterwards either.

The second one I first verified by wrapping two layers of duct tape
around a randomly chosen blade near the hub. If it is off in static
balance, it either will run smoother or rougher. That tells you the
next step. I finished having to put several coats of paint on the
back side of the lighter blade to get it to run smooth, but thought it
a helluva way to make a new 172 run right. Cessna picked up the
repair under warranty. Those were the days.....

If course you could also have prop roughness from unequal blade pitch,
or from the blades not being directly opposite each other (i. e. bent
like a boomerang).

If you have a similar driveline as my 172, it is also possible that
your prop is indexed wrong with respect to the engine crank. The
proper orientation should be described in the aircraft service manual.
The proper orientation is specific and some mechanics may not know
that. On my 172 facing the front of the A/C, it is to be at TDC when
the prop axis is at the 1:30 - 7:30 orientation.

Find out what is causing your problem. You'll save a lot of long term
agony.