PA-32-300 is 200 past TBO- poor climb and T/O Roll

flyin'gator

flyin'gator

Pre-takeoff checklist
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flyin'gator
All-
I am a member of a great club based at KFTW.
We have a 1975 Cherokee 6-300 which has an engine currently 225 past TBO. Oil analysis shows no metal, and compressions are all 70+. She came out of annual in OCT. However she does not hop off the ground well and climbs very poorly at or within 200 lbs of gross. Today, a few of us loaded her up and did a series of cruise, climb, and Takeoff tests- which all used calculated density altitudes and the book settings. Although we were 200 lbs shy of full gross, we never saw better than 65% of book Climb on the gross wt. curve, take off to clear a 50 obstacle was 25% longer than the zero wind curve at gross, and we had a 19kt direct headwind. Climb was 325 fpm from 4500 from 5500. Da at takeoff was 2400 field elevation was 852 at xbp- we calculated DA at each interval up the ladder. Some people in the club feel that the tach could be an issue- that the engine is not making the correct power (a linkage setting off the tach?) before we get to a firewall foreword rip out- are there any other items you would reccomend we look at? (Rigging isn't great too) any 6-300 owners out there with similar feedback after tbo?

Thanks in advance,

Rick
 
Not a 6 owner, but I have owned a Piper for several years and chased similar issues.

First and foremost, check your tach. Your RPM is the primary variable in performance. Mine was way off, replaced it with an EI electronic tach.

Check rigging. Pipers can be WAY out of rig without being obvious, and significantly impact performance through drag.

Also, make sure the pitot/static system is functioning properly. All your tests are based on time to climb, distance to climb, etc. If you're lifting off too early or too late or climbing above or below Vy, due to airspeed errors, that will dramatically effect the numbers you generate.

In cruise, is the IAS, TAS, GS, and fuel burn matching up? If there are drag problems, fuel burn would be higher than expected for airspeed, and airspeed lower than expected for RPM/MP.
If there the tach is reading higher than actual, airspeed would be lower than expected for RPM/MP, and fuel burn lower than expected for power setting.

Essentially, check the cheap stuff first before doing the expensive stuff. And make sure the tools you are using to measure performance (i.e. instruments) are accurate, otherwise you can't be sure of anything.
 
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Get an optical tach and see what your real numbers are. What is your real fuel flow vs. book fuel flow? (Actual fuel flow, not on the pressure based fuel flow off the factory gauge.)
 
Thanks guys!
We are going to begin with the tach and rigging.
Your feedback is greatly appreciated.


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Also check basic things like ignition timing.
 
And condition of the harness.
 
Ignition timing. Spark plugs. Harness. Weak or late spark really hurts.

Was the engine leaned somewhat for density altitude? Is the fuel system out of whack and giving the engine way too much fuel? What does the exhaust pipe look like? Really black?

Is the carb heat closing all the way?

Pipe mufflers had a problem with internal baffles coming loose and blocking the outlet. Sure holds the power back. With a constant-speed prop the RPM won't show that.

Dan
 
flyin'gator said:
All-
I am a member of a great club based at KFTW.
We have a 1975 Cherokee 6-300 which has an engine currently 225 past TBO. Oil analysis shows no metal, and compressions are all 70+. She came out of annual in OCT. However she does not hop off the ground well and climbs very poorly at or within 200 lbs of gross.
Click to expand...

I had a PA32-260 and it was never impressive at gross. If I rotated at book, it would wallow for a period of time. I pushed all the numbers up by ~5mph and that helped alot.

Other then that cavat, all the other suggestions are of merit, in particular timing and rpm.
 
We did lean for DA.
Pipe not too black, but not grey either.
I will suggest these checks to our mechanic.
Thanks again!


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Worn cam lobes? Wouldn't be unexpected with that much time since last overhaul, and would definitely account for low power output despite good compression, good ignition, good prop governor etc. Note that the prop governor, if operating properly, should be allowing the engine to turn full rated RPM no matter what your tach reads.
 
Jeff K said:
Wouldn't that show in the oil analysis though? OP said Oil analysis shows no metal.
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Not necessarily -- the total wear occurring over 2250 hours wouldn't show up much in one analysis. We're talking about water dripping on a rock for a thousand years, not rocks grinding together for a few minutes. That's also why you don't really notice the effect on performance over time -- too small a change over too long a period. Just one day someone else gets in the plane and says, "Gee, for a 300HP Six, this plane isn't performing like the others I've seen," and you realize s/he's right.
 
Ron Levy said:
Not necessarily -- the total wear occurring over 2250 hours wouldn't show up much in one analysis. We're talking about water dripping on a rock for a thousand years, not rocks grinding together for a few minutes. That's also why you don't really notice the effect on performance over time -- too small a change over too long a period. Just one day someone else gets in the plane and says, "Gee, for a 300HP Six, this plane isn't performing like the others I've seen," and you realize s/he's right.
Click to expand...

That isn't how camshafts wear. They are case hardened with only the outer few thousanths being hard and softer material beneath. If a cam was worn enough to significantly reduce valve timing, it would've worn into the softer material and would show up in oil analysis. When cam lobes go, they go pretty fast.
 
Ron Levy said:
Worn cam lobes? Wouldn't be unexpected with that much time since last overhaul, and would definitely account for low power output despite good compression, good ignition, good prop governor etc. Note that the prop governor, if operating properly, should be allowing the engine to turn full rated RPM no matter what your tach reads.
Click to expand...

not necessarily. Maintenance can adjust the governors. If the last guy doing the adjustment used the installed tach and it's not indicating accurately then the engine would in fact not be turning the correct rpm.
 
I vote for cam lobes too. You can take the rocker box covers off one side and measure the valve lift easily enough.
 
Why not? I did this myself just a few weeks ago.
 
Yep, that doesn't sound right. I'll throw a vote for cam too. Mine climbs well in those ranges. 12k + is a different story.
 
So we had the Tach checked out and it is within tolerances. We are going to check the rigging next. It's cold so she is performing for now, but by april she will struggle mightily again. Does anyone know of a texas/oklahoma/arkansas Piper rigging specialist? Are there shops that hold additional expertise in this area? After this we may be forced to go firewall forward for troubleshooting...
Thanks so much for everyone's input.

-Rick


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flyin'gator said:
All-
I am a member of a great club based at KFTW.
We have a 1975 Cherokee 6-300 which has an engine currently 225 past TBO. Oil analysis shows no metal, and compressions are all 70+. She came out of annual in OCT. However she does not hop off the ground well and climbs very poorly at or within 200 lbs of gross. Today, a few of us loaded her up and did a series of cruise, climb, and Takeoff tests- which all used calculated density altitudes and the book settings. Although we were 200 lbs shy of full gross, we never saw better than 65% of book Climb on the gross wt. curve, take off to clear a 50 obstacle was 25% longer than the zero wind curve at gross, and we had a 19kt direct headwind. Climb was 325 fpm from 4500 from 5500. Da at takeoff was 2400 field elevation was 852 at xbp- we calculated DA at each interval up the ladder. Some people in the club feel that the tach could be an issue- that the engine is not making the correct power (a linkage setting off the tach?) before we get to a firewall foreword rip out- are there any other items you would reccomend we look at? (Rigging isn't great too) any 6-300 owners out there with similar feedback after tbo?

Thanks in advance,

Rick
Click to expand...
Rick! How the heck are you? Been a while...
 
flyin'gator said:
. Does anyone know of a texas/oklahoma/arkansas Piper rigging specialist? Are there shops that hold additional expertise in this area?

-Rick


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Click to expand...

Piper singles are a piece of cake to rig. Adjust the flaps IAW the service manual then get the ailerons in trail with the flaps. Wing rigging is set at the factory.

The flap rigging tool can be made with a straight board and one screw.
 
So, like, what was the verdict? Did the airplane get fixed?

FWIW...

I happened to be in our materials lab this morning and I borrowed a section of a camshaft that had been polished (and tested) you can see the difference between the hardened outer portion and the softer inner portion so I grabbed the attached picture. (It's just a random automotive cam shaft from a junk yard.)
 

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Cool pic! Nice to see the hardened layer is relatively thick... I wonder how that compares to a Lycoming cam?

I should have my engine disassembled over the weekend, and I expect to find a lobe that is going round...we'll see.
 
Norman said:
Piper singles are a piece of cake to rig. Adjust the flaps IAW the service manual then get the ailerons in trail with the flaps. Wing rigging is set at the factory.

The flap rigging tool can be made with a straight board and one screw.
Click to expand...

No, you don't match the ailerons to the flaps. Both are set independently. Ailerons are set to neutral with the bell crank centered with the proper rigging tool. Flaps are set to neutral with the flap tool. The rudder is aligned at the same time. After a test flight, if a wing is heavy, then the flap, and only the flap, on that side is lowered until the plane flies straight. This is the correct way to do it, by the book, and also the way to reduce drag. Never match flaps and ailerons to each other or to the wingtip. If they line up, great, but that is not the correct way to do it. That way usually produces the worst handling and the slowest speeds. My specialty is rigging all types of planes for performance.
 
It could be that the engine isn't making rated power and if so valve lift, ignition timing, RPM, and fuel flow would all be suspects needing checking.

But another potential culprit that hasn't been mentioned AFaIK is weight. If the airplane as loaded weighs a few hundred pounds more than the W&B calculation indicates the climb performance would suffer significantly. Between people underestimating their own (fully clothed) weight, miscellaneous junk in the airplane, and the tendency for airplanes to gain empty weight over time I'd bet that putting the plane and people on a scale would show a discrepancy.
 
gismo said:
It could be that the engine isn't making rated power and if so valve lift, ignition timing, RPM, and fuel flow would all be suspects needing checking.

But another potential culprit that hasn't been mentioned AFaIK is weight. If the airplane as loaded weighs a few hundred pounds more than the W&B calculation indicates the climb performance would suffer significantly. Between people underestimating their own (fully clothed) weight, miscellaneous junk in the airplane, and the tendency for airplanes to gain empty weight over time I'd bet that putting the plane and people on a scale would show a discrepancy.
Click to expand...

True, I saw a plane with a belly full of rain that turned to ice before.
 
Henning said:
True, I saw a plane with a belly full of rain that turned to ice before.
Click to expand...

Ouch. That would not only add weight but introduce structural damage as the ice expanded.

Dan
 
Dan Thomas said:
Ouch. That would not only add weight but introduce structural damage as the ice expanded.

Dan
Click to expand...

Luckily it was a PA-12, tube and fabric, no damage. It would have been a ***** had I not noticed and started my pipeline run that day lol.
 
Checking rigging next them Manifold Pressure and Fuel system. As it is a club plane and the other aircraft was in Annual- the pace of troubleshooting has been slow...I only hope we find it before it gets hot here again in May...


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when we swapped out spark plugs that failed the resistance test I literally gained 6 knots and 300fpm . . . .that might help alot. As others have said try the cheapo stuff first . . . but consider that you will doing the engine in the next 400 hours regardless, right?
 
Yeah he engine has past TBO, but appears to be making the required power with good compressions and no abnormalities in the oil analysis is the club is attempting to locate the source of the problem prior to a firewall forward replacement in case that is not the core issue. Everyone understands the plane is not a rocket ship, but 200 fpm in 80f seems under safety margin.


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Diagnosed as worm Camshaft during annual last week as per suggested by Ron, Bruce et al.

Thanks everyone!
 
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