Lack of power in Cessna 172-R

Hi, all,

Could someone please provide some suggestions on this.

Last summer we bought a 1997 160 HP Cessna 172-R. The test flight
(with 3 adults) went just fine.

When I picked the plane up from the shop after the service (required
to fix certain things that needed it [such as a loose tail!], the
performance was very sluggish. It did not seem like the same plane -
quite underpowered.

Even below gross weight, it couldn't take off from a 2200' runway
without scaring the heck out of me thinking we weren't going to make
it. OK it was hot but the book said we should be over a 50' obstacle
at about 1800' - we were not even close!

All rpm indications were within spec (for static run-up, etc). When on
the takeoff roll, rpm was about 2100, which seemed low, but there is
no spec in the POH for rpm for the takeoff roll. The rpm went much
higher after we were cruising (2300 or so).

Also, there was a "burbling" sound from the exhaust.

The prop was removed, inspected and put back on (with pleanty of
scratch marks which weren't there before.

Any suggestions would be greatly appreciated.

TIA Chuck

Freedom Chuck - The Man of 1,000 Songs

see my website at: www.freedom-chuck.com

Hi, all,

Could someone please provide some suggestions on this.

Last summer we bought a 1997 160 HP Cessna 172-R. The test flight
(with 3 adults) went just fine.

When I picked the plane up from the shop after the service (required
to fix certain things that needed it [such as a loose tail!], the
performance was very sluggish. It did not seem like the same plane -
quite underpowered.

Even below gross weight, it couldn't take off from a 2200' runway
without scaring the heck out of me thinking we weren't going to make
it. OK it was hot but the book said we should be over a 50' obstacle
at about 1800' - we were not even close!

All rpm indications were within spec (for static run-up, etc). When on
the takeoff roll, rpm was about 2100, which seemed low, but there is
no spec in the POH for rpm for the takeoff roll. The rpm went much
higher after we were cruising (2300 or so).

Also, there was a "burbling" sound from the exhaust.

The prop was removed, inspected and put back on (with pleanty of
scratch marks which weren't there before.

Any suggestions would be greatly appreciated.

TIA Chuck

Do a compression check on all cylinders. Find out from the factory what RPM
you ought to get on full power static runup. When you get to know an
airplane and one day it seems sluggish, it probably is and you need to
figure out why.

All rpm indications were within spec (for static run-up, etc). When on
the takeoff roll, rpm was about 2100, which seemed low, but there is
no spec in the POH for rpm for the takeoff roll. The rpm went much
higher after we were cruising (2300 or so).

Look at the TCDS (3A12) and you'll find static RPM limits. Go he
http://www.airweb.faa.gov/Regulatory...keModel.nsf/0/
EE81A0B13ADB620986256E2B0054B119?OpenDocument

Static RPM, I would think - flame on, is a pretty good indication of overall
engine health. At least it's a place to start. Only 2100 during the takeoff
roll sounds like something ain't right.

Has it been this way since last Summer?

No Spam

Are you getting enough fuel flow/pressure?

--

Thx, {|;-)

Victor J. (Jim) Osborne, Jr.



take off my shoes to reply

If the lifters spall, become rough, and wear down the cam, there will be
almost no roughness. The engine will simply lose power as you describe. It
may make static RPM but not reach full RPM in cruise (it's a bit more
complex with a CS prop).

Oil analysis will not show the big pieces of metal that come off the lifters
and may miss the cam shaft wear as well. Have the filters been cut open and
carefully inspected at each oil change? It takes more than just a look.
They need to be drained and inspected very closely. Washing in solvent and
running a magnet around in the pail is recommended by some.

This is just one possibility but it's very much on my mind since our engine
is currently spread out on a rebuild bench.

--
Roger Long

Chuck wrote:
: Hi, all,

Hi Chuck!

: All rpm indications were within spec (for static run-up, etc). When on
: the takeoff roll, rpm was about 2100, which seemed low, but there is
: no spec in the POH for rpm for the takeoff roll. The rpm went much
: higher after we were cruising (2300 or so).

: Also, there was a "burbling" sound from the exhaust.

There have been numerous cases of the 172R's fuel injection running
excessively rich, causing poor idle, loss of power, etc. Do ground
witnesses see a trail of black smoke from the exhaust at full power?

You might want to ask a mechanic familiar with the 172R fuel injection
about how it might be tested.

IIRC, the 172S, the 180 HP version, has a much lower incidence of this
issue.

--
Aaron Coolidge (N9376J)

Chuck wrote:

Also, there was a "burbling" sound from the exhaust.

Fuel spilling in. It's running way too rich.

George Patterson
A diplomat is a person who can tell you to go to hell in such a way that
you look forward to the trip.

Hi, all,
First, I want to thank everyone who made suggestions.

Gary, a compression check was done on all cylinders and the
compression is fine. The power for a full-power static runup should be
2065 to 2165 with the mixture leaned for max rpm. The actual rpm is
about 2150.

No Spam, I could not get the website you gave me. Is there an
alternative one? I agree with you, 2100 rpm on the takeoff rull seems
a bit slow, but I don't know what the norm is for this plane.

Victor J. Osborne Jr., your question about fuel flow/pressure is
interesting. When starting you are supposed to advance the lean
control with the aux. fuel pump on to get about 3-5 gal/hr., then when
it starts, you turn off the aux. fuel pump. But once the engine
starts, I don't know what the fuel flow/pressure is. Do I read it on
the fuel flow gage?

Roger Long, I don't know if your "lifters" problem applies to this
plane because the cruise is fine. Just the take off and climb out is
sluggish. Since the compression is good, I'm assuming the engine is
ok. Am I mistaken?

Aaron Coolidge, your comment about the fuel injection is also
interesting. I will certainly ask our mechanic to check it (since the
plane is in for its annual anyways). I did not, however, notice loss
of power, but at minimum rpm (with the throttle full out) it does not
idle very well -- it feel like it's going to stop.

George Patterson, you say it's running way to rich. I was wondering
way you say this, but you just may be right. To correct this I


Once again, thanks to everyone.

Chuck



Freedom Chuck - The Man of 1,000 Songs

see my website at: www.freedom-chuck.com

"Gary" wrote in message ...


Also, there was a "burbling" sound from the exhaust.

Maybe loose baffle in muffler restricting the outlet. Could have
broken loose between the time you tried it and the time you took it
away.
Other things to check might be one mag retarded somewhat, perhaps
caused by a broken impulse coupling spring.
Did you try leaning the mixture a bit to see if there was better
RPM in the static runup?

Dan

Chuck wrote:

George Patterson, you say it's running way to rich. I was wondering
way you say this, but you just may be right. To correct this I

The "burbling" sound you report is typical of raw gas going through the engine
and igniting in the exhaust system. I'm not familiar with the injector system,
so I really can't help with troubleshooting. With a carbureted engine, you
could easily check this by leaning on the ground.

George Patterson
A diplomat is a person who can tell you to go to hell in such a way that
you look forward to the trip.