Rough Engine Concern

[George]

Great day for flying today...however my engine is causing me some concern!

First leg 60 miles at 5500ft seemed to run okay..with the exception of the number 4 EGT temp approx. 100 degrees higher than the others on the GEM.  Thought it might be a instrument problem and leaned the engine by watching for rpm drop and then increasing mixture (seemed to be in-line with remaining normal EGTs) and then turned my attention to my son navigating around some class B airspace.

Second leg took off and climbed to 2000ft and pulled the power back to 25 inches and then as I reduced RPM to 2500 the engine acted as if I were leaning the mixture and started occasionally running rough...as if it was too lean and I had not even touched the mixture yet. I don't recall what the GEM was indicating. Quickly turned back to airport and as I pulled power back as I entered the pattern it again ran rough for a second or two. 

Next flight I took the plane around the pattern by myself and it seemed fine. EGTs all approx. same temp...no major difference as on first leg.

So I headed 35 miles back home at 4500ft at 23 inches and 2300 rpm. I did not start the leaning process until level at 4500 and it seemed like the EGTs were peaking with very little movement of the mixture control?? Again the number 4 cylinder seemed higher than the rest of the cylinders. Pulled power back to around 20 inches as I started to descend and the engine roughness was back so I increased power back to 23/23 which seemed to get rid of roughness. As I entered the pattern and reduced power once again the 1 to 2 second bouts of roughness which seemed to go away as power was backed to around 11-12 inches.  

Needless to say the aircraft is tied up until we can fix the problem.

- O-360 engine 500 SMOH 

- Mag checks prior to each take off were about 50 rpm drop L&R.

- Left mag overhauled 50 hours ago.

- New plugs all cylinders 15 hours ago.

- Wednesday night Thursday morning  flew 11 hours and ran great..all EGTs and other temps seemed to be in order

- Fuel pressure high end of green w/o boost pump.

- Teaspoon or two of water removed prior to first leg out of each tank. Engine roughness happened on both L and R tanks. No fuel added during this trip.

 

Looking forward to your ideas of what might be going on with this engine.

 

Thanks a bunch..

GHW

 

 

Edited January 14, 2017 by George
spelling

[Dham]

D you know what your fuel flow was? Had something similar and it was the fuel flow divider the diaphragm had a cut in it.


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[larryb]

I think it is possible there is still water in the tanks.

[takair]

I think Larry may be right.  It is difficult to get all of the water out.  At higher power it could be drawing in globules of water.  Could also have some at the bowl of the carb.  Water will give you a good scare and drive you crazy.  Each time I've experienced it, a reduction in power got me back and I didn't find the water immediately.  If you are routinely getting that much water in the fuel, have your caps fixed.  It takes very little water to give you a good scare and only a little more to stop the engine.  I think that you will find that the 100 split in EGT is quite normal for carb equipped aircraft and even some fuel injected. It is ultimately the trend that needs to be looked at with EGT.   I would start with the water. Let it settle out, and drain. Then grab the wing tip and bump the wings up and down and drain again.  Don't forget the gascolator.  Drain it into a clear container and see if you get water there.  If you were fuel injected I would Even recommend pulling the fuel servo screen.  Don't recall an easy way to inspect the fuel bowl...

[tigers2007]

Maybe rock your wings with one person on each side? I had to do this in my C150 to clear out the water and debris in the tanks. It shook it up good enough and did a good job. I would rock it good after each flight and would get a little more water/sediment the next morning.


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[gfor]

Teaspoon...... seriously????


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[gfor]

Let's go back to the teaspoon...... unreal! Drain the thing! If fuel cost is a consideration pour it back in the tank. Don't let 15 cents kill you....


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[tigers2007]

If you pour it back in, it should be fine with one of these:

Mr. Funnel AF8CB Fuel Filter https://www.amazon.com/dp/B000SOKE5E/ref=cm_sw_r_cp_api_ZwGxybF2GDY08


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[Yetti]

How old are the O rings in the fuel caps?

[George]

 I hope or wish it was as easy as water in the tanks but my boys and I are pretty thorough when checking for water in fuel. We do rock the wings to help any water that may be in the tank work it's way to the sumps. I did sump the fuel prior to last leg home in which I found a trace of water about the size of a BB on right tank only. Flew home in left. We do not pour sump fuel back in tanks. 

Sumped again this am with no traces of water.

Not sure on the age of O rings.. will check.

Thanks for input.

GHW

 

 

[larryb]

My shop replaces the fuel tank O rings every annual.

[Bennett]

My shop replaces the fuel tank O rings every annual.

LASAR replaces mine every year as part of the annual. The airplane is hangared, and the tanks filled after every flight, and in three years I have never seen any trace of water when I sump the tanks as part of my preflight. Just good preventive maintenance at relatively little cost.


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[jetdriven]

If you replace them with blue fluorosilcone O-rings they will last a decade or longer. It's just a superior martial than nitrile rubber 

[Bob_Belville]

1 hour ago, jetdriven said:

If you replace them with blue fluorosilcone O-rings they will last a decade or longer. It's just a superior martial than nitrile rubber 

Mine are still passing muster at annual, 5 years that I know of.

[Marauder]

1 hour ago, Bob_Belville said:

Mine are still passing muster at annual, 5 years that I know of.

Bob -- what is the part number for these? As far as I know, mine have never been changed on my bladder tanks. 

[bradp]

If you replace them with blue fluorosilcone O-rings they will last a decade or longer. It's just a superior martial than nitrile rubber 

But most mechanics will test the fuel caps as part of the annual inspection and replace your pretty blue fluorosilicone o rings with standard :-(


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[Bob_Belville]

2 minutes ago, Marauder said:

Bob -- what is the part number for these? As far as I know, mine have never been changed on my bladder tanks. 

I have electronic parts manuals on this computer but our fuel caps are part of the O&N STC aren't they? I'll have to check when I'm at the airport tomorrow.

(There are two listed in the manual - MS29513-010 MS29513-338 but I don't know if either of them is what we have. I think there's a small o-ring on the shaft as well as the large one we're talking about.)

[bradp]

George notes a non normal mixture sweep to peak.

Thinking about the "differential diagnosis" and the symptom- should consider spark and more likely injection / servo fuel delivery issues if you can rule out lingering water.

Do you have an engine monitor and can you upload the data?

Have you tried doing a LOP magneto check? What kind of mags do you have?

Are all cylinders peaking together or is one too lean (induction leak, fuel injector blockage) or too rich?

Just PP thoughts as Anthony says


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[tony]

Why did you overhaul the mag?  When the engine was running rough did you do an inflight mag check?  I would suspect the  mag that was rebuilt 50 hours ago.  A bad cap in the mag  would have similar symptoms.  

[Marauder]

2 hours ago, Bob_Belville said:

I have electronic parts manuals on this computer but our fuel caps are part of the O&N STC aren't they? I'll have to check when I'm at the airport tomorrow.

(There are two listed in the manual - MS29513-010 MS29513-338 but I don't know if either of them is what we have. I think there's a small o-ring on the shaft as well as the large one we're talking about.)

Yep, there should be a small O ring on the shaft and then the big one.

[Bob_Belville]

17 minutes ago, Marauder said:

Yep, there should be a small O ring on the shaft and then the big one.

https://www.aircraftspruce.com/pages/ep/orings/fuelorings2.php

But I don't think the ASpruce part is the blue flurosilicone.  I think this is what we have: Military Standard M25988-1-338 O-Ring Fluorosilicone - 70A

[Hank]

31 minutes ago, Marauder said:

Yep, there should be a small O ring on the shaft and then the big one.

Yeah, the little one is the -010, the big one is the -338. I'm thinking about getting the new type, not nitrile or fluorosis icons, but something else I can't remember that's also fuel resistant (if I can find them by next month).

[takair]

A little DC4 goes a long way to preserving the large oring and helping to keep out water.  I would think petroleum jelly works as well. Talking just a trace amount on the oring.  This does not help with the smaller inner orings, but a drop of oil there helps.  i have used DC 4 on door seals as well with good luck.

[Marauder]

59 minutes ago, Bob_Belville said:

https://www.aircraftspruce.com/pages/ep/orings/fuelorings2.php

But I don't think the ASpruce part is the blue flurosilicone.  I think this is what we have: Military Standard M25988-1-338 O-Ring Fluorosilicone - 70A

Bob -- I think the big O rings on our bladder caps call for the fluorosilicone ones. I saw them at one time on the Aircraft Spruce site but can't find them now. They were expensive, something like $50 each. 

I will call the new owners of the bladder STC and ask what should be used. I know I also saw someone on Beechtalk selling them. I will look for that information as well.

[jetdriven]

The Shaw aero bladder cap o-rings are not the same size as the Beech ones or the ones listed in the Mooney IPC. However someone on here did find the right ones at Spruce for a little less than the price from O&N, which was like 110$ for all 4. Yikes.