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PA-28-180 Low power query



 
 
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  #12  
Old October 2nd 08, 03:14 PM posted to rec.aviation.owning
The Visitor
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Posts: 231
Default PA-28-180 Low power query

have your engine guages been checked?
Could it just be a governor adjustment?

John






wrote:
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


  #13  
Old October 2nd 08, 10:30 PM posted to rec.aviation.owning
[email protected]
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Posts: 193
Default PA-28-180 Low power query

The Visitor wrote:
: have your engine guages been checked?
: Could it just be a governor adjustment?

: John

Fixed-pitch prop, so no governor. I've checked the tach with a calibrated strobe tach.

-Cory

--

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

  #14  
Old October 7th 08, 01:28 PM posted to rec.aviation.owning
The Visitor
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Posts: 231
Default PA-28-180 Low power query

Opps, sorry. I'm used to the conversion with a constant speed prop.
It was an Avcon conversion.

John

wrote:
The Visitor wrote:
: have your engine guages been checked?
: Could it just be a governor adjustment?

: John

Fixed-pitch prop, so no governor. I've checked the tach with a calibrated strobe tach.

-Cory


  #15  
Old October 7th 08, 01:59 PM posted to rec.aviation.owning
[email protected]
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Posts: 193
Default PA-28-180 Low power query

The Visitor wrote:
: Opps, sorry. I'm used to the conversion with a constant speed prop.
: It was an Avcon conversion.

Same STC covers both fixed and constant-speed installations.

-Cory

--

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

 




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