R-985 not making rated RPM

KRyan

KRyan

Pre-takeoff checklist
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KRyan
OK, here's the story I have so far . . .

Engine removed from a Weatherly 620B and sent off for overhaul. All reports show that the original engine was operating "normally" but was due TBO.

An engine came back from the O/H shop (don't know if it was the original O/H engine or an exchange, but don't think that's relavant at this time, anyway). The mechanic installed the carburetor, mags, propeller, etc. removed from the original engine on the "new" engine and installed it in the aircraft.

The engine will not make static RPM - its running about 500 RPM to low. this particular prop is in low pitch (high RPM) with no governor oil pressure, and the mechanic has verified that he is getting 0 psi output to the prop with the prop control lever full forward, so the prop should be in low pitch and should be allowing the engine to reach static RPM at max throttle, but he cannot reach static RPM.

The engine shop says the engine checked out OK at their place, but that was with their mags, carb, and test club prop.

Anybody have any idea what could be wrong here? Remember that the components removed from the old engine (that was running "fine") were installed on this "new" engine as well.
 
KRyan said:
OK, here's the story I have so far . . .

Engine removed from a Weatherly 620B and sent off for overhaul. All reports show that the original engine was operating "normally" but was due TBO.

An engine came back from the O/H shop (don't know if it was the original O/H engine or an exchange, but don't think that's relavant at this time, anyway). The mechanic installed the carburetor, mags, propeller, etc. removed from the original engine on the "new" engine and installed it in the aircraft.

The engine will not make static RPM - its running about 500 RPM to low. this particular prop is in low pitch (high RPM) with no governor oil pressure, and the mechanic has verified that he is getting 0 psi output to the prop with the prop control lever full forward, so the prop should be in low pitch and should be allowing the engine to reach static RPM at max throttle, but he cannot reach static RPM.

The engine shop says the engine checked out OK at their place, but that was with their mags, carb, and test club prop.

Anybody have any idea what could be wrong here? Remember that the components removed from the old engine (that was running "fine") were installed on this "new" engine as well.
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Cam timing is the first place I would look and work your way up from there. With a 500rpm discrepancy on a fresh engine, you have to start at the cam timing because everything else sets from there and it's pretty likely. I'm guessing you haven't flown it to see how it's doing otherwise besides just RPM loss? Any more running symptoms/anomalies you can describe?
 
Is the prop really in low pitch?
Is the mag timming really correct?
 
See if you can borrow their mag, and carb since it made static rpm on their test stand. Either that or someone's instrumentation is off.
 
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Henning said:
Cam timing is the first place I would look and work your way up from there. With a 500rpm discrepancy on a fresh engine, you have to start at the cam timing because everything else sets from there and it's pretty likely. I'm guessing you haven't flown it to see how it's doing otherwise besides just RPM loss? Any more running symptoms/anomalies you can describe?
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If the Cam ring was out of time it would not make the numbers on the cell. remember test clubs are fixed pitch.
 
Tom-D said:
If the Cam ring was out of time it would not make the numbers on the cell. remember test clubs are fixed pitch.
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That would trust and assume far too much to not check. If I didn't set the timing and check it on a degree wheel myself and it's not making power, it's suspect. It's not difficult to check cam timing and it's too critical to be correct to not check. There was the guy on the Red Board that had the cam a tooth off on his new engine. He described the symptoms I told him it was the cam at first, they checked everything multiple times (for God knows how much money) for months. They finally checked the cam, sure as s-t, there it was.

I don't care how unlikely, whenever a new engine isn't doing what it's supposed to, the first place I start is from the cam timing since it is the basis of timing everything else. Then I work my way up from the base. It's the very basic precept of engine diagnostics.
 
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Henning said:
That would trust and assume far too much to not check. If I didn't set the timing and check it on a degree wheel myself and it's not making power, it's suspect. It's not difficult to check cam timing and it's too critical to be correct to not check. There was the guy on the Red Board that had the cam a tooth off on his new engine. He described the symptoms I told him it was the cam at first, they checked everything multiple times (for God knows how much money) for months. They finally checked the cam, sure as s-t, there it was.

I don't care how unlikely, whenever a new engine isn't doing what it's supposed to, the first place I start is from the cam timing since it is the basis of timing everything else. Then I work my way up from the base. It's the very basic precept of engine diagnostics.
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I'll wager that engine was rebuilt in the field and tested on the aircraft, and not run on the cell.

The 985 has about a dozen props that can be used on it, and as many carbs, with different venturies.

there are a long list of things that cause a power loss on a new engine installation, so unless we have hands on access, it is simply a guessing game.

I'm with Brien 23, who's tach were they using?
 
Tom-D said:
I'll wager that engine was rebuilt in the field and tested on the aircraft, and not run on the cell.

The 985 has about a dozen props that can be used on it, and as many carbs, with different venturies.

there are a long list of things that cause a power loss on a new engine installation, so unless we have hands on access, it is simply a guessing game.

I'm with Brien 23, who's tach were they using?
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Engine removed from a Weatherly 620B and sent off for overhaul. All reports show that the original engine was operating "normally" but was due TBO.

An engine came back from the O/H shop (don't know if it was the original O/H engine or an exchange, but don't think that's relavant at this time, anyway). The mechanic installed the carburetor, mags, propeller, etc. removed from the original engine on the "new" engine and installed it in the aircraft.
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I wouldn't assume that the engine was ever run before the first time I heard it run, people lie all the time.

As you say, it's a guessing game. All of diagnostics is. The trick it to order your guesses so that you start at the beginning, work your way up from there and make sure that everything you check is on a firm footing.

It could be anything, but the place to START is the cam timing otherwise you risk wasting too much time. Diagnostics isn't about finding the problem eventually, diagnostics is about finding the problem ASAP which means you have to order your tests in the most efficient manner and not skip steps that may make you back up. Just because it's not likely doesn't mean you don't check it when the symptom fits.
 
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The aircraft is in Texas, more than 1000 miles away from me here in Ohio. I called the mechanic and asked him if there were any other abnormalities during the run-up, and he told me that "every now and again" when the get into higher RPMs "it'll pop a little bit."

I told him to check the cam timing, and he was glad for the advice. I'll let you know how it turns out. Thanks for the help, guys!
 
KRyan said:
I told him to check the cam timing, and he was glad for the advice. I'll let you know how it turns out. Thanks for the help, guys!
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If he doesn't know to check it, I doubt he knows how to check it.
 
Pop at higher RPM tells me that unburned fuel is going out the exhaust, so the ignition timing could be late, the mixture could be wrong or the cam timing could be off.

That helps push my mind away from the prop.
 
Skylane81E said:
Pop at higher RPM tells me that unburned fuel is going out the exhaust, so the ignition timing could be late, the mixture could be wrong or the cam timing could be off.

That helps push my mind away from the prop.
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That tells me he's running way too rich.
 
KRyan said:
The aircraft is in Texas, more than 1000 miles away from me here in Ohio. I called the mechanic and asked him if there were any other abnormalities during the run-up, and he told me that "every now and again" when the get into higher RPMs "it'll pop a little bit."

I told him to check the cam timing, and he was glad for the advice. I'll let you know how it turns out. Thanks for the help, guys!
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Definitely cam, that was the missing clue.
 
Both of the guys I'm working with are in their 80's. The main mechanic told me he has lots of radial engine eperience, but apparently all of it on multi row engines. He told me he's got a lot of R2800 time. I'm inclined to think that if you can handle 18 cylinders that nine would be a snap!

I asked him if he knew how to check the cam timing, he got a little indignant!
 
Henning said:
Definitely cam, that was the missing clue.
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Cam timing doesn't change from the test stand to the aircraft.

Why would it not pop and run the numbers on the stand and not on the aircraft?
 
KRyan said:
Both of the guys I'm working with are in their 80's. The main mechanic told me he has lots of radial engine eperience, but apparently all of it on multi row engines. He told me he's got a lot of R2800 time. I'm inclined to think that if you can handle 18 cylinders that nine would be a snap!

I asked him if he knew how to check the cam timing, he got a little indignant!
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IMO there's one place to send a 985 and that's to Covington.
 
KRyan said:
Both of the guys I'm working with are in their 80's. The main mechanic told me he has lots of radial engine eperience, but apparently all of it on multi row engines. He told me he's got a lot of R2800 time. I'm inclined to think that if you can handle 18 cylinders that nine would be a snap!

I asked him if he knew how to check the cam timing, he got a little indignant!
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No doubt, It's like asking your teenager if they know how to blow their nose.
 
another thing to check is back to the prop. If the oil lines are disconnected or the governor disabled that still doesn't account for weights or other prop features that tend to change the pitch. Its supposed to go to low pitch when pressure is lost unless its for a twin when it may go to high pitch on the way to feather. . .
Still worth checking. I've seen a couple situations where props were thought to be set at low pitch only to find they were drifting and creating ground run issues.


Frank
 
Well, to quote Henning "people lie all the time." They decided to check the low pitch blade angle on the prop. Keep in mind that this is the same propeller (supposedly) that was taken off the engine that they TBO'd. That prop on that engine (reportedly) did just fine.

They checked blade angle. It was 22 degrees. It's supposed to be 16 degrees. I doubt it "ran fine" at a high blade angle on the old engine either.
 
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