rough running C-182

Can anyone suggest a cause for a slight roughness in a well maintained O-470
(1958 C-182). The mechanic has checked both mags and harness wires and
plugs, installed a rebuild carb and balanced the prop (which required very
little correction). In flight checks of carb heat, mags and unlocking the
primer pump all show no effect. Roughness appears above 20" MP at any RPM.
Engine mount checks ok.

Any suggestions would be welcome.
R Kyle

induction leak. If it has a manifold pressure gauge check the sensor
line. It may be broken.
Michelle

R&A Kyle wrote:

Can anyone suggest a cause for a slight roughness in a well maintained O-470
(1958 C-182). The mechanic has checked both mags and harness wires and
plugs, installed a rebuild carb and balanced the prop (which required very
little correction). In flight checks of carb heat, mags and unlocking the
primer pump all show no effect. Roughness appears above 20" MP at any RPM.
Engine mount checks ok.

Any suggestions would be welcome.
R Kyle





--

Michelle P ATP-ASEL, CP-AMEL, and AMT-A&P

"Elisabeth" a Maule M-7-235B (no two are alike)

Volunteer Pilot, Angel Flight Mid-Atlantic

Volunteer Builder, Habitat for Humanity

"R&A Kyle" wrote in message news:1HCkd.12833$z_4.9667@trnddc07...
Can anyone suggest a cause for a slight roughness in a well maintained O-470
(1958 C-182). The mechanic has checked both mags and harness wires and
plugs, installed a rebuild carb and balanced the prop (which required very
little correction). In flight checks of carb heat, mags and unlocking the
primer pump all show no effect. Roughness appears above 20" MP at any RPM.
Engine mount checks ok.

Any suggestions would be welcome.
R Kyle


Plugs are worth checking again. We've had lots of trouble with
Champs in the past, and went to Auburn/Unison plugs years ago because
they were so much better. Now we're finding the Unisons arcing in the
shield barrel when the pressure reaches 120 or so, and the spark
weakens sooner and causes roughness at climb or cruise settings. A
month ago I installed a full new set in one of our airplanes and the
roughness cleared up immediately.

Dan

Possibly a cam lobe has worn nearly flat? I heard of an O-320H2AD
that did that. It would idle but not produce power.

A spark plug that is broken internally will cause this at high power
settings. Find a spark plug tester that uses air pressure and fires
the plugs under pressure to test the plugs.

A bad plug wire or a mag that is arcing internally will also cause a
problem.

A quick mag bearing check is to do a mag check at idle rpm. If the
RPM drops are not the same and it is rough then the mag bearings are
loose and the rotor is flopping around changing the timing.

John

On Thu, 11 Nov 2004 05:23:09 GMT, "R&A Kyle"
wrote:

Can anyone suggest a cause for a slight roughness in a well maintained O-470
(1958 C-182). The mechanic has checked both mags and harness wires and
plugs, installed a rebuild carb and balanced the prop (which required very
little correction). In flight checks of carb heat, mags and unlocking the
primer pump all show no effect. Roughness appears above 20" MP at any RPM.
Engine mount checks ok.

Any suggestions would be welcome.
R Kyle

On Fri, 12 Nov 2004 03:16:35 GMT, (John_F) wrote:

A spark plug that is broken internally will cause this at high power
settings. Find a spark plug tester that uses air pressure and fires
the plugs under pressure to test the plugs.

I've had bad plugs that have passed that test. I think a problem is that
the pressure in those testers is only a fraction of the pressure that
exists in the cylinder. But it is a place to start.

The problem was rough running. The affected cylinder and plug was
determined by a multi-probe EGT and running on single-mag. The plug passed
the 'test' in the box. But the engine ran properly after that plug was
replaced.


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

On Fri, 12 Nov 2004 07:43:34 -0500, Ron Rosenfeld
wrote:

On Fri, 12 Nov 2004 03:16:35 GMT, (John_F) wrote:

A spark plug that is broken internally will cause this at high power
settings. Find a spark plug tester that uses air pressure and fires
the plugs under pressure to test the plugs.

I've had bad plugs that have passed that test. I think a problem is that
the pressure in those testers is only a fraction of the pressure that
exists in the cylinder. But it is a place to start.

The problem was rough running. The affected cylinder and plug was
determined by a multi-probe EGT and running on single-mag. The plug passed
the 'test' in the box. But the engine ran properly after that plug was
replaced.


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

Ditto. Those air pressurized testers/cleaners can't begin to
adequately emulate the actual pressure/heat a sparkplug
is subject to while the engine is making 70% (or whatever)
power at cruise.

I had a plug that would go off line intermittently, but with a 6-cyl
Continental, all I noticed was a slight drop in RPM @ cruise.

Bela P. Havasreti

Bela P. Havasreti wrote in message ...
On Fri, 12 Nov 2004 07:43:34 -0500, Ron Rosenfeld
wrote:

On Fri, 12 Nov 2004 03:16:35 GMT, (John_F) wrote:

A spark plug that is broken internally will cause this at high power
settings. Find a spark plug tester that uses air pressure and fires
the plugs under pressure to test the plugs.

I've had bad plugs that have passed that test. I think a problem is that
the pressure in those testers is only a fraction of the pressure that
exists in the cylinder. But it is a place to start.

The problem was rough running. The affected cylinder and plug was
determined by a multi-probe EGT and running on single-mag. The plug passed
the 'test' in the box. But the engine ran properly after that plug was
replaced.


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

Ditto. Those air pressurized testers/cleaners can't begin to
adequately emulate the actual pressure/heat a sparkplug
is subject to while the engine is making 70% (or whatever)
power at cruise.

I had a plug that would go off line intermittently, but with a 6-cyl
Continental, all I noticed was a slight drop in RPM @ cruise.

Bela P. Havasreti

Typical compression pressures are what the plug has to deal with,
though at elevated temps, as you say. An 8:1 compression ratio will
produce 120 psi or so at TDC, and that's where we test our plugs and
often find them failing at that point. Even if it's only one plug in a
cylinder that's missing, roughness will show in many engines. If the
engine data specifies mags timed at two different angles, the
later-timed plug may not fire because the cylinder pressure is already
higher, with combustion underway.

Dan

How are you perceiving the roughness?

How you know the engine mounts are OK?

Kent Felkins
Tulsa



"R&A Kyle" wrote in message
news:1HCkd.12833$z_4.9667@trnddc07...
Can anyone suggest a cause for a slight roughness in a well maintained
O-470
(1958 C-182). The mechanic has checked both mags and harness wires and
plugs, installed a rebuild carb and balanced the prop (which required very
little correction). In flight checks of carb heat, mags and unlocking the
primer pump all show no effect. Roughness appears above 20" MP at any
RPM.
Engine mount checks ok.

Any suggestions would be welcome.
R Kyle

First, thanks for all these comments. The roughness is enough to cause a
low level of vibration in the airframe; not enough to terminate the flight,
but the needles do dance. Another IA, not familiar with this plane, made a
short flight and agreed. The roughness is not steady, but rather comes in
waves, 3 or 4 seconds of rough followed by a slightly shorter interval of
somewhat smoother operation. (I realize this is very subjective.)

We systematically changed mix, MP, RPM, carb heat, mags and primer pump
(lock/unlock). Roughness appears only above 20 in MP. No correlation with
other inputs.
"Fly" wrote in message
...
How are you perceiving the roughness?

How you know the engine mounts are OK?

Kent Felkins
Tulsa



"R&A Kyle" wrote in message
news:1HCkd.12833$z_4.9667@trnddc07...
Can anyone suggest a cause for a slight roughness in a well maintained
O-470
(1958 C-182). The mechanic has checked both mags and harness wires and
plugs, installed a rebuild carb and balanced the prop (which required
very
little correction). In flight checks of carb heat, mags and unlocking
the
primer pump all show no effect. Roughness appears above 20" MP at any
RPM.
Engine mount checks ok.

Any suggestions would be welcome.
R Kyle