Engine issues?

[1RTK1]

When at the right rpm on my o-360 I can make my mixture knob act as a throttle with no roughness ever detected.

 

[MarkH]

Was the carb cleaned after the jugs were?

The green valves suggest a lean mixture, and a previous issue was buildup in the chambers. If the contaminate stuck to the fuel system, it could lead it running lean (or worse, inconsistent) now.

 

[Tom-D]

My POH indicates that 25 LOP is acceptable .

When you are measuring with a micrometer, don't cut with a chainsaw.

 

[FlySince9]

When you are measuring with a micrometer, don't cut with a chainsaw.

Not sure what that means...at least not in this context.

 

[Matthew Rogers]

I think it is "when you are cutting with a chainsaw, don't bother measuring with a micrometer".

 

[Doug Reid]

What Tom is saying is that is is not practical to attempt to set the mixture to a precise EGT setting using a single uncalibrated EGT gage. It sounds to me like the other cylinders are reaching peak before the gage indicates peak on this cylinder. I am wondering if the engine is running too lean...maybe an intake leak ? I would not have removed cylinders over a white residue ? Mogas usually leaves a dark deposit...100ll leaves a grey deposit.

 

[FlySince9]

It sounds to me like the other cylinders are reaching peak before the gage indicates peak on this cylinder.

I’m sure that’s the issue. Plane just finished annual. No engine issues reported. But with a carbureted engine, I’m not surprised other cylinders may be past peak before the gauged one. That’s why I’m looking forward to the engine monitor to see what each cylinder is doing... Still don’t get the chainsaw/micrometer analogy, though...

 

[Doug Reid]

You have to be an old guy to understand......

 

[Salty]

When you’re communicating with Sanskrit don’t use the Internet.

 

[FlySince9]

You have to be an old guy to understand......

65 isn’t old enough?

 

[Tom-D]

What Tom is saying is that is is not practical to attempt to set the mixture to a precise EGT setting using a single uncalibrated EGT gage. It sounds to me like the other cylinders are reaching peak before the gage indicates peak on this cylinder. I am wondering if the engine is running too lean...maybe an intake leak ? I would not have removed cylinders over a white residue ? Mogas usually leaves a dark deposit...100ll leaves a grey deposit.

I'm saying, that no carb'ed engine will get the mixture of all cylinders close to enough to run without having one or more in the red box.

I’m sure that’s the issue. Plane just finished annual. No engine issues reported. But with a carbureted engine, I’m not surprised other cylinders may be past peak before the gauged one. That’s why I’m looking forward to the engine monitor to see what each cylinder is doing... Still don’t get the chainsaw/micrometer analogy, though...

Does the engine develop full power? fuel metering will see the combustion color change.

 

[Briar Rabbit]

Update to my friend’s engine issues - the fuel tests came back. The fuel was contaminated with small and dissolved particles of fuel filter element from the airport or delivery truck system. So the white coating in his engine was melted plastic residue from a disintegrated fuel filter element. I also had the same thoughts as MarkH and suggested to him to request his A&P go through the carburetor to look for filter debris. I think this could have caused sporadic flow through the carburetor jet and changes in his fuel air mixture also explaining why he was experiencing engine roughness when he reduced power during letdown. If the engine was sporadically leaning itself without his involvement he might not have noticed it on his egt. And this likely caused the green color on his exhaust valves? He has notified the Phillips SD airport manager of a pending claim. My suggestion to him is to insist they replace the exhaust valves and valve seats, a carburetor overhaul in addition to the $6,000 he has already spent on pulling the jugs the first time to clean up the white residue.

Ironically I had a problem in my airplane with fuel filter debris 1 1/2 years ago from a different airport. But my engine is fuel injected (IO520) and I have a JPI-930 engine monitor. A contaminant partially blocked a much smaller fuel injector. The engine monitor alerted me to the issue immediately and the first time I was able to push in the mixture control to get the cht back down below 400F. I had the injector cleaned but then it happened again to a different injector on the subsequent flight, fortunately within a few miles of my home airport on the return trip. I ended up having both tanks cleaned (one of them twice) and had to replace the entire fuel injector system, again twice, before the issues went away. It is hard to clean small debris from 45 gallon wing tanks!

My friend is pricing engine monitors for his airplane. I am wondering if filter contamination happens more often than we realize? In my friends case he is a CFII flying his own airplane that he is very familiar with and quick to notice something not quite right. If it was not his airplane or if he was a low time pilot (or student) he might not have been so quick to notice and the airplane could have been flown for another hundred hours until a potential exhaust valve failure? And the tell tale signs of the cause long gone?

I have learned to only purchase fuel from airports with above ground storage tanks. They have potential to drain debris from the bottom of the tank easier. This reduces the odds of getting contaminants and less likely to plug the fuel filters. And without partially plugging the fuel filter less likely to blow out a chunk of the filter element when pumping fuel which is what happened in my case. Filter particles were recovered in my injector system and screens. Enlarged photo attached, these elements will snake through a screen!

 

[Tom-D]

after all this, clean the carb finger screen too. (it should not show anything)

 

[Tom-D]

My suggestion to him is to insist they replace the exhaust valves and valve seats, a carburetor overhaul in addition to the $6,000 he has already spent on pulling the jugs the first time to clean up the white residue.

WHY? clean fuel should remedy the problem.

 

[Kenny Phillips]

More like the engine likely won’t run smoothly at a lean enough mixture that would hurt it.

Yeah, this. We regularly leaned our O-300 (172F) until it ran rough, then screwed it in until it smoothed out. The head temps never did anything weird, and fuel burn was under eight gallons per hour (at a deeeeee-luxe 105 KIAS). That engine is very smooth, so you can tell quickly if it's not quite right.

 

[Briar Rabbit]

WHY? clean fuel should remedy the problem.

WHY? clean fuel should remedy the problem.

My thought is that if the exhaust valves are green in color they probably were too hot. Does not sound like they burnt the edges since the green color is in the center of the valves, but to be safe that the valve does not have any internal heat stress cracks or grain modifications where the mushroom head meets up with the stem it might be a good precaution - especially if the insurance company will pay for it? The lower transformation range for steels start at about 1,350F and extends up to the upper transformation range at 1,675F for the lowest carbon steels and as the carbon increases in steel the upper transformation range decreases below 1,400F. Between the lower and upper transformation ranges steel can experience modifications in integrity and potentially permanent warping. At slightly over 1,400F steels change internally from a body centered cube lattice to a face centered cube lattice turning into gama centered austenite grains (they also become non magnetic until they cool back down below the lower critical), but integrity is likely affected. If steel reaches 1,800F (classed as the bottom of the forging range) integrity is definitely gone. So if the engine was operated too lean how long do you think it would take for the exhaust valves to reach 1,400 degrees? I don't know but don't think it would be a bad precaution to put in new exhaust valves. My thought is if there was 1/32" of white plastic residue melted inside the engine combustion chamber there must have been quite a bit of filter element going through that carburetor jet.

Please share your thoughts what you would request of the insurance company if you are hauling your family and grand-kids in this bird? I may be overly cautious.

 

[Hang 4]

I'd be skeptical of a mech that said "let's run some MMO in the fuel and oil and see if it gets better (post on prior page)

 

[Tom-D]

My thought is that if the exhaust valves are green in color they probably were too hot. Does not sound like they burnt the edges since the green color is in the center of the valves, but to be safe that the valve does not have any internal heat stress cracks or grain modifications where the mushroom head meets up with the stem it might be a good precaution - especially if the insurance company will pay for it? The lower transformation range for steels start at about 1,350F and extends up to the upper transformation range at 1,675F for the lowest carbon steels and as the carbon increases in steel the upper transformation range decreases below 1,400F. Between the lower and upper transformation ranges steel can experience modifications in integrity and potentially permanent warping. At slightly over 1,400F steels change internally from a body centered cube lattice to a face centered cube lattice turning into gama centered austenite grains (they also become non magnetic until they cool back down below the lower critical), but integrity is likely affected. If steel reaches 1,800F (classed as the bottom of the forging range) integrity is definitely gone. So if the engine was operated too lean how long do you think it would take for the exhaust valves to reach 1,400 degrees? I don't know but don't think it would be a bad precaution to put in new exhaust valves. My thought is if there was 1/32" of white plastic residue melted inside the engine combustion chamber there must have been quite a bit of filter element going through that carburetor jet.

Please share your thoughts what you would request of the insurance company if you are hauling your family and grand-kids in this bird? I may be overly cautious.

Too much info run it, see what happens.

 

[Doug Reid]

Ray’s Rule of Precision...measure with micrometer, mark with chalk, cut with an axe.

It is an old saying....like Murphy’s Laws....

It is used to describe a futile attempt at precision....