Engine issue O-360

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flycapt2310

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flycapt2310
Hi all…
I have an issue in a new engine. The aircraft is a Diamond Da40 FP with a Lycoming o-360. The flight school purchased an overhauled engine from a local shop. Since day one we have had a power issue…
When applying power the engine RPM will come up normal to about 2200 RPM as you continue to advance the throttle the engine will start to stumble back and loose RPM. With full throttle the engine RPM is low 1900’s. With full throttle we should be at about 2300 RPM (static – on the ground no forward motion). If we pull the mixture back we can get more power out of the engine but never what the old engine did.
This has been going on for a month and half our mechanic and engine builder has been trying to resolve the issue. Diamond and Lycoming have 2 different carburetors that they say can be used on the engine. The diamond carb has more fuel going into the engine. This is what was on the previous engine and it ran great. Lycoming said to use a carb with a little less fuel. So we changed over to the smaller carb. We got a 50 to 80 percent increase in engine RPM. So now with full throttle we are at high 1900’s. If we pull the mixture back a little we can get up to mid 2100 RPM.
We then started isolating extra systems…
Carburetor heat was disengaged to make sure it wasn’t leaking hot air at high power settings, no fix.
Engine driven fuel pump was inspected – we hooked up a fuel pressure gauge to it to make sure it was the correct pressure it was 5 psi (which is the correct psi). No fix
Magnetos were changed, and engine timing was confirmed correct. No fix
We changed the wire harness to make sure it wasn’t a bad wire. No fix
We disengaged the fuel primer. No fix. I also ran the engine and then turned the fuel primer on (its electric solenoid) it flooded the engine as it should.
Mixture cable throw is set full rich to full idle.
Throttle cable throw is set full open to idle stop.
Changes spark plugs. No fix.
Check valve springs – nothing broken
When we changes spark plugs we noticed that the number 2 cylinder bottom plug was excessively rich. So pulled the rocker cover and looked at the springs no issue. We pulled the springs off and found the intake valve to stick a little so we changed the number 2 cylinder.
When we ran it up next we gained 100 RPM, BUT still at full power we are seeing a drop in RPM. So were now at high 2100 RPM at full throttle. If we pull the mixture back we can get up to 2200 RPM.
We then thought that maybe we had a stuck lifter. We changed all the lifters in the other cylinders and confirmed that the push-rod tubes were all the correct length. NO FIX
We then pulled the engine back off the plane and send it back to the shop. He opened it up inspected his internal timing which was correct but checked it again. Changed the cam-shaft, inspected all the cylinders, valves, valve guides, cylinder size, and anything else he could measure.
We just reinstalled the engine and same problem…. What now???
We are at full power with 2100-2150 RPM. In-between all the test we have test flown the aircraft. It stays at that lower power the entire time during climb and will produce more power once level. If we keep the mixture back we can get mid 2200 RPM out of it. It should right after takeoff produce 2400 + RPM as soon as we break ground.
 
Hmmmmm..

I would have made a compression check on the first motor before teardown... Sounds like you guys have done about all you can, hopefully the engine builder is truthful too....

First guess would be to confirm it has the correct pistons in it and not lower compression ones..:dunno:

No chance that someone did a sneaky prop change with greater pitch ?
 
We did do a compression they were all high 70's. Our engine guy checked for correct pistons and bore size. we isnspected the prop. its the same.
 
Check your cam timing before you spend to much time chasing your tail around, a tooth off causes these problems, and this wouldn't be the first time I've seen it.
 
If the RPM comes up with throttle application and then recedes with further application, it isn't compression or prop pitch. That pretty well isolates it to fuel/air mixture, which strongly suggests carburetor, or induction leak, or mixture control. BTW, what does the AFM say is the permissible range for RPM at full throttle on static run-up?
 
I'm wondering if it is an actual loss of power or an indication problem. Have you checked it with a digital hand held?

Tell me more about the two carbs. Does it have the original carb on it now or was it replaced?

When you replaced the cam, did you buy the correct cam, and check the lift. Did you change the lifters?
 
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I'd pull it off send it to Charley Malot, and bill the rebuilder.
 
Did the rebuilder run it in a test cell after you sent it back? If so, did he have the same problem? If he didn't run it, why not.
You said you disengaged the carb heat cable but did you inspect to see if it is sealing out the hot air from the air box?
 
Before disassembling the engine, I would have tried a different carb which would be my next step.
 
Just had a customer shop solve a wierd power loss problem. A Cherokee 235 was intermittantly losing 10 MPH in cruise with no indication change on anything except speed. It could be made up advancing the throttle. Turns out it had a loose screw in the on/off valve mechanism on a manifold suction operated standby vacuum system. Other than that this sounds like a cam timing problem. We have seen mismarked cams and gears! Charlie Melot Zephyr Engines
 
p-thomas said:
Before disassembling the engine, I would have tried a different carb which would be my next step.
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Me too, I can't believe you had the entire engine disassembled and never tried a different carburetor.

EDIT: oops - sorry, I missed that you did try another carb. Disregard this post.
 
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we did try a new carb. 2 actually. We put the lycoming carb on and that helped a little but didn't fix it. We then put the carb from out old engine on to try it. We had the same result as the first one.
 
And when we sent the engine back he changes the cam. so there is less chance we had 2 bad cams that produced the same resluts.
 
You are saying that it reaches 2200 rpm at part throttle and drops to 1900 at full throttle
Then you changed ONE cylinder with a tight valve and gained 100 - so now it is up to 2200 and down to 2000.
Then after a huge thrash you are now getting 2200 inflight by leaning it hard.
You have changed cams
You have changed carbs.
You have changed magnetos and wires.
About the only thing left is binding in the accessory case or the cylinders

Being that one cylinder was a problem, all cylinders are suspect - 4 new Titans would put that to rest.

Engine has to be put on a dyno where it can be run at full throttle while checks are being made.

And it has to go to a new shop for that.
I had a remanufactured carb that went back three times and was pronounced perfect three times - except it kept pouring out gas and setting the engine on fire - annoying to say the least in a wood Super Viking.
The last time the owner of the carb facility said he personally tested and flow inspected the carb and that WE were the problem.
When I finally blew a gasket and took the carb apart myself (voiding the so called warranty) I immediately saw the missing cotter pin on the float pivot rod which allowed the rod to vibrate out far enough to drop one side of the pivot ears off the rod and let the carb flood. A ten cent cotter pin and 5 years on the engine still purrs like a kitten. He did a beautiful job of remanufacturing, it was just his inspecting that was crap.;
 
Henning said:
Check your cam timing before you spend to much time chasing your tail around, a tooth off causes these problems, and this wouldn't be the first time I've seen it.
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Repost. Cam is a tooth off....
 
I get so tired of this. When you have an overlap problem, all 4- it's the CAM. The mechanic is a maroon. He just doesn't want to look because of teh expense and time involved.... he needs replaced.
 
flycapt2310 said:
And when we sent the engine back he changes the cam. so there is less chance we had 2 bad cams that produced the same resluts.
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Does this engine exhibit the same symptom on the test stand?

Did you replace the induction hoses during the engine overhaul?

Is the airbox door working as it should?

is the airfilter the cause?

has the muffler been checked for loose baffles?

Has the muffler AD been complied with?
 
True that on the muffler, definitely worth a look. If the cam was right, that's next. Timing is the basis to every thing, always check there first, it's cheapest as well. Muffler is next.
 
OK.... we found it. It was an exhaust blockage. We checked the baffling in the exhaust several times... We probably had the exhaust off 4 times every time looking it in and shaking it around to see if there were any loose parts. I got a set of test straight pipes to put on the engine. When we took it off the exhaust this time we heard something rattling around in it. Test stacks on and the engine went right up to 2300 RPM static. Which is 200 RPM more than it ever did, and the correct amount for the engine. The exhaust is one solid welded piece. We can’t inspect it without cutting it in half. Thank you for all your help…
 
Take this opportunity to consider a Powerflow for increased fuel economy.
 
flycapt2310 said:
OK.... we found it. It was an exhaust blockage. We checked the baffling in the exhaust several times... We probably had the exhaust off 4 times every time looking it in and shaking it around to see if there were any loose parts. I got a set of test straight pipes to put on the engine. When we took it off the exhaust this time we heard something rattling around in it. Test stacks on and the engine went right up to 2300 RPM static. Which is 200 RPM more than it ever did, and the correct amount for the engine. The exhaust is one solid welded piece. We can’t inspect it without cutting it in half. Thank you for all your help…
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Well now,,, Isn't it nice when proper trouble shooting procedures are applied.
 
This is a typical exhaust blockage problem. Mechanics have spent hours chasing their tail and forget to look up the tail pipe for blockage.
 
Tom-D said:
A bore scope up your pipe will give ya a better look.
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I've heard about bad people like you on the InterWebz from mom and dad.

You stay away from my pipe! No means no! ;)

(Yeah, I'm making tailpipe jokes. I'm bored.)

Chevy Chase does it better anyway... Mooooon River...

 
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