PA-28-180 Low power query

Hey all. As some of you may recall, about a year ago I posted a question regarding two different power loss issues I was having
with my PA-28-140 with an O-360-A4A 180hp upgraded engine. I'll summarize what's transpired and figure to get some opinions on what I
might try next.

Basically, I had an intermittent slightly low power on about 1 in 25 takeoffs. Not enough to make you abort, but enough to realize
upon climbout that it wasn't quite doing what it usually did in terms fo FPM. Never rough, did mag checks, fuel pressure good, EGT
correct, CHT correct, etc, etc... just a little low on power, and after a minute or so it would quietly come back. After checking cam
lift and lifters, etc, I realized that the dry tappet clearance was too much on about 5 of the 8 pushrods. I fixed that, and the problem
has not come back after a year.

The *other* problem is that this engine has never been very strong. It's always been barely able to make the minimum static RPM
required by the TCDS, and climbs out at about 2400 RPM at Vy. This problem persists.... it feels more like a -160 than a -180 and I've
checked all sorts of things that would be common:

- Compressions great... 78/80-80/80 on all four chrome cylinders. No hissing out exhaust or crankcase.
- Mags internally timed when we replaced the points and condensers, and externally set at 25 degrees as per spec
- Does it with new plugs.
- Manifold pressure (added as part of the engine upgrade and measured at the intake port on #3) is good for full-power takeoff... about
1-1.5" or so less than the ambient pressure (e.g. 30.00 altimeter here at 2100' MSL airport gives me about 26.5-27" MP on takeoff)
- EGT reads 1350 on all cylinders at full rich, so it's not starved for fuel.
- Fuel pressure stays at 3-4 psi.
- Does it on 100LL or 93 AKI cargas or any mixture of the two.
- Did the "wobble test" SB on the valves. Acceptable, although somewhat worn.
- Brand new exhaust system... no change
- Measured cam lift last year... all lobes show 0.353" +- 0.002"... not a worn cam as that's the same as a friend's brand new Superior
cam.
- Propeller is stock, 60" pitch and brand new when we got the plane. I believe it's 60" as other than full-power, the POH is dead-balls on
as far as airspeed and fuel burn are concerned. Any other pitch prop and those wouldn't be right.

SO.... my thinking is this. I was skeptical that the dry tappet clearance could affect the intermittent power problem, since the
hydraulic lifters should be able to compensate for this while running. I appeared to be in error as fixing the dry tappet clearance to
spec seems to have cleared this up (took me a year to really believe that). The original overhaul on this engine happened before we bought
it was definately a field overhaul... probably more or less a "service limits" overhaul. Any chance that if the lifters are mismatched
from a shoddy overhaul that they'd bleed down too quickly and cause a chronic low power from insufficient valve lift? If I could buy a new
set of lifters to fix the problem, I'd be a happy guy!

Any other ideas to entertain? I'm open to suggestions... this has been p*ssing me off for literally *YEARS*!

Thanks,
-Cory

--

************************************************** ***********************
* Cory Papenfuss, Ph.D. Electrical Engineering, PPSEL-IA *
* Research Associate, Vibrations and Acoustics Laboratory *
* Mechanical Engineering *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

wrote in message
...
Hey all. As some of you may recall, about a year ago I posted a question
regarding two different power loss issues I was having
with my PA-28-140 with an O-360-A4A 180hp upgraded engine. I'll summarize
what's transpired and figure to get some opinions on what I
might try next.

Basically, I had an intermittent slightly low power on about 1 in 25
takeoffs. Not enough to make you abort, but enough to realize
upon climbout that it wasn't quite doing what it usually did in terms fo
FPM. Never rough, did mag checks, fuel pressure good, EGT
correct, CHT correct, etc, etc... just a little low on power, and after a
minute or so it would quietly come back. After checking cam
lift and lifters, etc, I realized that the dry tappet clearance was too
much on about 5 of the 8 pushrods. I fixed that, and the problem
has not come back after a year.

snip

Some of the things that might be helpful to specify are the conditions you
are experiencing this condition. For instance, you mentioned your airport
is 2100 MSL, but what was the density altitude? What FPM are you getting?
Are you leaning at all prior to takeoff or during the climb?

You mentioned EGTs on all cylinders, so I'm assuming you have a full engine
analyzer. Most of these have a download function. What I suggest you do is
take a normal flight and carefully note all the conditions of your flight,
then do a download of the data. You might try shooting an email to Walter
Atkinson over at advancedpilot.com. Walter participates in a number of
forums and he's quite helpful.

Does the best ROC indicated airspeed change with the engine and prop
upgrade? If it did and you are flying the old numbers, perhaps that is
affecting your performance.

Regards,
Mike.

http://flickr.com/photos/mikenoel/

http://photoshow.comcast.net/mikenoel


wrote in message
...
Hey all. As some of you may recall, about a year ago I posted a question
regarding two different power loss issues I was having
with my PA-28-140 with an O-360-A4A 180hp upgraded engine. I'll summarize
what's transpired and figure to get some opinions on what I
might try next.

Basically, I had an intermittent slightly low power on about 1 in 25
takeoffs. Not enough to make you abort, but enough to realize
upon climbout that it wasn't quite doing what it usually did in terms fo
FPM. Never rough, did mag checks, fuel pressure good, EGT
correct, CHT correct, etc, etc... just a little low on power, and after a
minute or so it would quietly come back. After checking cam
lift and lifters, etc, I realized that the dry tappet clearance was too
much on about 5 of the 8 pushrods. I fixed that, and the problem
has not come back after a year.

The *other* problem is that this engine has never been very strong. It's
always been barely able to make the minimum static RPM
required by the TCDS, and climbs out at about 2400 RPM at Vy. This
problem persists.... it feels more like a -160 than a -180 and I've
checked all sorts of things that would be common:

- Compressions great... 78/80-80/80 on all four chrome cylinders. No
hissing out exhaust or crankcase.
- Mags internally timed when we replaced the points and condensers, and
externally set at 25 degrees as per spec
- Does it with new plugs.
- Manifold pressure (added as part of the engine upgrade and measured at
the intake port on #3) is good for full-power takeoff... about
1-1.5" or so less than the ambient pressure (e.g. 30.00 altimeter here at
2100' MSL airport gives me about 26.5-27" MP on takeoff)
- EGT reads 1350 on all cylinders at full rich, so it's not starved for
fuel.
- Fuel pressure stays at 3-4 psi.
- Does it on 100LL or 93 AKI cargas or any mixture of the two.
- Did the "wobble test" SB on the valves. Acceptable, although somewhat
worn.
- Brand new exhaust system... no change
- Measured cam lift last year... all lobes show 0.353" +- 0.002"... not a
worn cam as that's the same as a friend's brand new Superior
cam.
- Propeller is stock, 60" pitch and brand new when we got the plane. I
believe it's 60" as other than full-power, the POH is dead-balls on
as far as airspeed and fuel burn are concerned. Any other pitch prop and
those wouldn't be right.

SO.... my thinking is this. I was skeptical that the dry tappet clearance
could affect the intermittent power problem, since the
hydraulic lifters should be able to compensate for this while running. I
appeared to be in error as fixing the dry tappet clearance to
spec seems to have cleared this up (took me a year to really believe
that). The original overhaul on this engine happened before we bought
it was definately a field overhaul... probably more or less a "service
limits" overhaul. Any chance that if the lifters are mismatched
from a shoddy overhaul that they'd bleed down too quickly and cause a
chronic low power from insufficient valve lift? If I could buy a new
set of lifters to fix the problem, I'd be a happy guy!

Any other ideas to entertain? I'm open to suggestions... this has been
p*ssing me off for literally *YEARS*!

Thanks,
-Cory

--

************************************************** ***********************
* Cory Papenfuss, Ph.D. Electrical Engineering, PPSEL-IA *
* Research Associate, Vibrations and Acoustics Laboratory *
* Mechanical Engineering *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

: Some of the things that might be helpful to specify are the conditions you
: are experiencing this condition. For instance, you mentioned your airport
: is 2100 MSL, but what was the density altitude? What FPM are you getting?
: Are you leaning at all prior to takeoff or during the climb?

: You mentioned EGTs on all cylinders, so I'm assuming you have a full engine
: analyzer. Most of these have a download function. What I suggest you do is
: take a normal flight and carefully note all the conditions of your flight,
: then do a download of the data. You might try shooting an email to Walter
: Atkinson over at advancedpilot.com. Walter participates in a number of
: forums and he's quite helpful.

I doubt that DA is the issue. Of course it has more power at sea-level DA, but still not what it should have as per the static
runup. I've done the DA calculations whenever I'm trying to figure out any true performance as per the book value. I know that few
airplanes match the performance listed in the POH, but they shouldn't be *dangerous* if loaded to gross, and the static RPM should remove
all aerodynamic airframe possibilities (out-of-rig, extra drag, etc).

I do not have an analyzer, but a single gauge and multiple probes on a switch. Also, since I run autogas often, if it were starved
for fuel it would probably have detonated by now. Oh, and yes... I do lean for the DA when necessary (like in the summer when DA can reach
as high as 4500').

Cheers,
-Cory

--

************************************************** ***********************
* Cory Papenfuss, Ph.D. Electrical Engineering, PPSEL-IA *
* Research Associate, Vibrations and Acoustics Laboratory *
* Mechanical Engineering *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

Mike Noel wrote:
: Does the best ROC indicated airspeed change with the engine and prop
: upgrade? If it did and you are flying the old numbers, perhaps that is
: affecting your performance.

: Regards,
: Mike.

Nope... it didn't change with the upgrade. A -180C POH is what was included with the engine upgrade (performed by the previous
owner 15 years ago, BTW), and that's what I'm following.

Again though... it's not just aerodynamic results that indicate low power, although there are plenty of those:
- ROC of ~500-600fpm at my max of 2200#. A stock -180 at 2400# is listed as 750... at 200lbs MORE weight
- Takeoff run probably ~20% longer than the book values... again at 2200#
- Top speed is about 8 mph less than book value (corrected for DA)
- WOT RPM at top speed is about 150 RPM below the book "max speed" curve.

The static RPM is also consistent with being probably 10-20 HP less than 180. Oh, and before anyone asks, I've checked the
tachometer for accuracy with a strobe, and overhauled/calibrated the ASI and VSI, and have no leaks in the pitot or static system.

Cheers,
-Cory




--

************************************************** ***********************
* Cory Papenfuss, Ph.D. Electrical Engineering, PPSEL-IA *
* Research Associate, Vibrations and Acoustics Laboratory *
* Mechanical Engineering *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

Can you make a static test? Tie tail to large spring scale/load cell,
run it up and observe result...

[This is inspired by my memory of a drag test on the Gossamer Condor;
they used a spring scale in the tow line...]

Then at least you can examine variable without test flights.
--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

David Lesher wrote:

: Can you make a static test? Tie tail to large spring scale/load cell,
: run it up and observe result...

: [This is inspired by my memory of a drag test on the Gossamer Condor;
: they used a spring scale in the tow line...]

: Then at least you can examine variable without test flights.
: --
I could, but aside from the variable of changing to a different propeller, a static runup will basically tell me the same thing.
Besides, I'm out of ideas on what to try (except for the hydraulic lifters which I meantioned in my first email).

-Cory

--

************************************************** ***********************
* Cory Papenfuss, Ph.D. Electrical Engineering, PPSEL-IA *
* Research Associate, Vibrations and Acoustics Laboratory *
* Mechanical Engineering *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

wrote:
I could, but aside from the variable of changing to a different propeller, a static runup will basically tell me the same thing.
Besides, I'm out of ideas on what to try (except for the hydraulic lifters which I meantioned in my first email).

Have you checked the muffler? A partial obstruction in the muffler
could result in lost power.

(just a shot in the dark...)

Bob Noel writes:

wrote:

I could, but aside from the variable of changing to a different
propeller, a static runup will basically tell me the same thing.
Besides, I'm out of ideas on what to try (except for the hydraulic
lifters which I meantioned in my first email).

Have you checked the muffler? A partial obstruction in the muffler
could result in lost power.

(just a shot in the dark...)


But a good one. I'm still thinking carb but that's without justification.

I've heard of using exhaust gas analyzers to look at the exhaust
for mixture.

I forget, has someone verified the value timing?



--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

: Have you checked the muffler? A partial obstruction in the muffler
: could result in lost power.

: (just a shot in the dark...)


: But a good one. I'm still thinking carb but that's without justification.

: I've heard of using exhaust gas analyzers to look at the exhaust
: for mixture.

: I forget, has someone verified the value timing?

Valve timing? Unchecked, but it seems like if it were out by a tooth on the cam, it wouldn't be able to make static RPM... barely
or not.

Muffler's been replaced as of last year due to other reasons. Performance unchanged.

-Cory

--

************************************************** ***********************
* Cory Papenfuss, Ph.D. Electrical Engineering, PPSEL-IA *
* Research Associate, Vibrations and Acoustics Laboratory *
* Mechanical Engineering *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************