Cylinder peaks way behind others

[lithium366]

I have a puzzle for you.
#4 cylinder peaks when other 3 cylinders are 50-60 degrees on a lean side

that cylinder EGT is also 100 degrees higher then other 3 when leaned ROP.

borescoping #4 shows a lot of deposits (expected if it runs reach all the time?)
 

So far I swapped EGT probes (cyl #4 still an outlier), did a fuel flow test, cleaned injector nozzles and also tried swapping injector nozzles. 
 

Checked in-flight ignition - ok.

Next I would like to exclude an induction leak but weird part is that when I am WOT vs partially open #4 has most EGT changes. I would expect the opposite unless #4 is okay and the other 3 cylinders have induction leaks…

Thinking about measuring dry tappet clearance but really don’t want to do this

Any ideas?

 

Edited April 26, 2023 by lithium366

[Shadrach]

7 hours ago, lithium366 said:

I have a puzzle for you.
#4 cylinder peaks when other 3 cylinders are 50-60 degrees on a lean side

that cylinder EGT is also 100 degrees higher then other 3 when leaned ROP.

borescoping #4 shows a lot of deposits (expected if it runs reach all the time?)
 

So far I swapped EGT probes (cyl #4 still an outlier), did a fuel flow test, cleaned injector nozzles and also tried swapping injector nozzles. 
 

Checked in-flight ignition - ok.

Next I would like to exclude an induction leak but weird part is that when I am WOT vs partially open #4 has most EGT changes. I would expect the opposite unless #4 is okay and the other 3 cylinders have induction leaks…

Thinking about measuring dry tappet clearance but really don’t want to do this

Any ideas?

 

An induction leak would likely make #4 run leaner, not richer and it would have minimal effect at full throttle. 

It might be helpful to know the full power, full rich EGT number. It should fall between 1150-1250.  If you compare full rich EGT to peek EGT you can determine how rich that cylinder is compared to the others. I would also consider doing the baby food jar test to see how the flows compare.

[A64Pilot]

Low compression raises peak EGT, but does not effect when a cylinder peaks. Said another way a high compression motor will have lower peak temps than a low compression motor

That cylinder is running richer than the others as evidenced by peaking late and I suspect is lower in compression by having a higher peak temp. Other things like timing etc can affect peak temp, but everything that can that I can think of except compression should affect all cylinders, not just one.

inductions leaks etc won’t change peak, will of course affect when peak occurs though.

The concept of Gami injectors is that different cylinders for different reasons will require more or less fuel to peak at the same time as the other cylinders and you match injectors of different flow rates to cylinders that require different rate to “balance”

Ideally factory injectors are identical, so if you have perfect factory injectors swapping them around won’t make any difference, of course there is variation so moving them around can make some difference.

Note, a leak down test AKA compression test gives a good idea, but doesn’t necessarily perfectly duplicate actual running compression or blow-by, that is to say it’s not uncommon for a cylinder that has good compression numbers to have a lot of blow-by.

I have a C-85 that has high blow-by as evidenced by turning the oil black quickly, high oil temps and excessively greasy belly, but is relatively low time and has good compression numbers “for a Continental”

On edit, before I slapped Gami’s on it, I’d try to find out what’s wrong and correct the problem, you may be onto something with valves though, if you have access to a dial indicator I’d check lift, it’s easy to do.

[wombat]

I think @lithium366 has put quite a bit of thought into this. 

I agree with everyone that cylinder #4 is running rich, for the various reasons mentioned.

He said he already did a fuel flow test and even tried swapping injectors.  For me, that would confirm that the same amount of fuel per second is flowing to that cylinder. So... That leaves a reduction in the amount of air as the only other option as to why this cylinder is running rich.        As he mentioned, valve clearances could be an issue.  If the intake valve doesn't open as far as the rest of the cylinders, when the valve is open the mixture entering the cylinder will be richer than the others.  

I don't have any good ideas.   A couple of bad ones that are really far fetched.

• Intake manifold partially blocked for just that cylinder?
• Exhaust manifold partially blocked for just that cylinder?
• Fuel injector lines for the other three cylinders all partially blocked by the same amount, so not restricted in low-flow applications, but only at high fuel flows?  But blocking three of four by the same amount and in a way that doesn't get identified by the fuel flow test is unreasonable.

Does the EGT peak difference happen at all power settings equally, or does it change if you lean at lower power vs. higher power?

[Fly Boomer]

9 hours ago, lithium366 said:

cylinder EGT is also 100 degrees higher then other 3 when leaned ROP.
borescoping #4 shows a lot of deposits (expected if it runs reach all the time?)
So far I swapped EGT probes (cyl #4 still an outlier), did a fuel flow test, cleaned injector nozzles and also tried swapping injectors

I admit that I don't know as much about this as others, but high EGT on a single cylinder might suggest fuel/air mixture still burning when it passes the EGT probe.  Incomplete combustion in the cylinder could be caused by one bad plug, one bad harness lead, or a magneto not working correctly?

[lithium366]

@Pilot64 how do I use a dial indicator to check an amount of valve lift?

@wombat I suspect there might be an excessive cam wear on that particular cylinder, I have other signs of cam/lifter issues too, but not to the point of needing an overhaul. What does not align is that if it’s an intake valve that does not open fully - how #3 is not having similar issues since it is sharing the same cam lobe?

@Fly Boomer I did a magneto check and cleaned / re-gapped all spark plugs

 

to everyone else, observations were uploaded to Savvy previously. The suggested checking if cylinder “breathe” normally. I will do another test flight and upload here as well

 

Edited April 26, 2023 by lithium366

[wombat]

@lithium366 Perhaps it's not the cam that's worn but the tappet or some other connecting pin or part?  But this is just going back to what you said at the very beginning.

Found this article about measuring dry tappet clearance.   Sounds like a bit of a hassle.   https://www.kitplanes.com/maintenance-matters-36/

[lithium366]

@wombat maybe a particular tappet / hydraulic lifter. That I can check, just putting it aside until I ruled out other obvious reasons

[A64Pilot]

To check valve lift remove the valve covers off of two cylinders, using the dial indicator slowly turn the prop with all upper spark plugs removed and measure the lift.

Then measure the lift of the valves on the other cylinder to compare it to, they ought to be nearly identical.

I’m not saying this is your issue, just it’s easy to rule out without spending any money, if you have a dual indicator. It can be done with a caliper just have to be a little creative

 

[lithium366]

@A64Pilot Lycoming manual says reading will be incorrect because of hydraulic lifters that need to be pulled, washed and dried. Is that true or approximation will be good enough? 

Edited April 26, 2023 by lithium366

[A64Pilot]

In my opinion if you have a serious enough problem it will be apparent. We aren’t trying to be precise here, close is good enough, and it’s surprising how close they are. Your looking for a gross difference, not a couple of thou, but ten times that or more

Also of course most of the time a spalling cam or lifters show up in the oil filter.

But realize this is just opinion. It’s quite surprising at how bad a cam can be and the engine run OK.

You have run a compression check to check for a badly leaking valve?

Trying cheap / easy tests first, like plugs, have you checked for resistance of the plugs? I believe a bad plug can raise EGT, but of course should fail the mag check

[lithium366]

@A64Pilot yes, cleaned, gapped and checked resistance

[Guest]

Based on another recent thread, do you have the correct fuel nozzles?  I’ve seen the newer two piece version with a missing stainless insert.

[lithium366]

@M20Doc my nozzles are 1 piece and don’t have a separate restrictor. I don’t know if this is ok or not since when I google a part number different pictures came up - with and without restrictor. I am assuming if it is a problem I should expect issues in all cylinders

[lithium366]

10 hours ago, Evan said:

It would be nice to know your GAMI spread as well. 

Attaching an image if Savvy profile flight - 3 leaning followed by mag check. GAMI spread is 07-08. Cylinders 1-3 have very little GAMI spread

[Shadrach]

10 hours ago, A64Pilot said:

Low compression raises peak EGT, but does not effect when a cylinder peaks. Said another way a high compression motor will have lower peak temps than a low compression motor

That cylinder is running richer than the others as evidenced by peaking late and I suspect is lower in compression by having a higher peak temp. Other things like timing etc can affect peak temp, but everything that can that I can think of except compression should affect all cylinders, not just one.

inductions leaks etc won’t change peak, will of course affect when peak occurs though.

The concept of Gami injectors is that different cylinders for different reasons will require more or less fuel to peak at the same time as the other cylinders and you match injectors of different flow rates to cylinders that require different rate to “balance”

Ideally factory injectors are identical, so if you have perfect factory injectors swapping them around won’t make any difference, of course there is variation so moving them around can make some difference.

Note, a leak down test AKA compression test gives a good idea, but doesn’t necessarily perfectly duplicate actual running compression or blow-by, that is to say it’s not uncommon for a cylinder that has good compression numbers to have a lot of blow-by.

I have a C-85 that has high blow-by as evidenced by turning the oil black quickly, high oil temps and excessively greasy belly, but is relatively low time and has good compression numbers “for a Continental”

On edit, before I slapped Gami’s on it, I’d try to find out what’s wrong and correct the problem, you may be onto something with valves though, if you have access to a dial indicator I’d check lift, it’s easy to do.

EGT numbers track compression ratio, not compression readings .I don’t think compression reading make a measurable.  Low compression readings in and of themselves have almost no effect on power. It’s a myth. That piston is firing 20 times a second in cruise. Whether it’s 80/80 or 40/80 it makes the same power. Increased Oil burn for sure, I’ve seen no evidence at soft compressions have any measurable effect on thermal efficiency which is why EGTs track compression ratio.

[Guest]

6 hours ago, lithium366 said:

@A64Pilot Lycoming manual says reading will be incorrect because of hydraulic lifters that need to be pulled, washed and dried. Is that true or approximation will be good enough? 

You should be able to measure the lift of the rocker arms without worrying about dry tappet clearance.  The lifters should remain pumped up after shut down. Lift on intake valves should be the same on opposite cylinder because they share the same lobe, so you’ll need to compare cylinder 2 to cylinder 4. 
I question exhaust valve lobe wear, but can’t yet twist my mind around your issue with EGT.

Excess tappet clearance should result in a noisy engine, too little should result in leaking valves.

[A64Pilot]

26 minutes ago, Shadrach said:

EGT numbers track compression ratio, not compression readings .I don’t think compression reading make a measurable.  Low compression readings in and of themselves have almost no effect on power. It’s a myth. That piston is firing 20 times a second in cruise. Whether it’s 80/80 or 40/80 it makes the same power. Increased Oil burn for sure, I’ve seen no evidence at soft compressions have any measurable effect on thermal efficiency which is why EGTs track compression ratio.

Cylinders with excessive wear, broken compression rings etc, do in fact lose compression and can do so to the point that they don’t even operate anymore, but before they get that bad, they lose power

In fact the big corn cob radials of old it wasn’t uncommon to fly aircraft with dead cylinders, from a loss of compression.

You can believe it’s a myth, but worn engines do lose power.

However leak down tests are not really a very good way to determine wear or ring seating, why? it’s because 80 PSI when compared to running cylinder pressures is trivial, and often simply isn’t enough to blow the rings out to make a good seal, so an engine with very low compression when tested with a leak down tester may not in fact have a lot of blow-by and compression loss when running, but if it does have excessive blow-by it does in fact have a loss of compression and lower compression does decrease power output.

But we aren’t talking lack of power here but a cylinder that peaks 100f higher than the others, other than ignition or compression I can’t come up with a reason it peaks higher can you?

I think it unlikely it has a wrong piston or a cylinder that the combustion chamber is so much larger than the others, possible, but unlikely. A leaking valve could reduce compression, or one not opening enough to completely fill the cylinder could.

He has ruled out plugs, incorrect fuel flow from his fuel flow test, although I can’t see how an improper injector could increase peak and he’s ruled out plugs although I’d rotate them anyway just to verify, easy and no money involved.

So other than compression and ignition, what else increases the temp at which a cylinder peaks? He also eliminated a bad probe by swapping probes and I don’t remember but assume they are all equidistant 

 

 

[lithium366]

@A64Pilot my thinking is that if I eliminated fuel issues, then it is air. If intake valve does not open fully - less air, reacher cylinder. But why higher EGTs? Can a worn lobe change ignition so much on that cylinder? 
 

@M20Doc if anything it is IO-360-A1A with 1-2, 3-4 sitting on same intake lobes. Will setting TDC after shutdown un-pump lifters? What points on rockers you suggest to measure and compare to? Or it is a similar test to dry tappet clearance just without removing them?

Edited April 27, 2023 by lithium366

[Rmfriday]

If one cylinder has a higher EGT then the rest wouldn’t that mean it is potentially running with either more air or less fuel then the other 3 cylinders?

if fuel has already been ruled out I would check and double check for a source of addition air.

fyi, I a, late to this party and not nearly as well versed as other who have commented.

[Guest]

47 minutes ago, lithium366 said:

@A64Pilot my thinking is that if I eliminated fuel issues, then it is air. If intake valve does not open fully - less air, reacher cylinder. But why higher EGTs? Can a worn lobe change ignition so much on that cylinder? 
 

@M20Doc if anything it is IO-360-A1A with 1-2, 3-4 sitting on same intake lobes. Will setting TDC after shutdown un-pump lifters? What points on rockers you suggest to measure and compare to? Or it is a similar test to dry tappet clearance just without removing them?

You are correct on the lifter and cylinder layout.  On shut down, those cylinders with valves open will be applying valve spring pressures against the lifters, a worn lifter may slowly bleed down increasing tappet clearance, until it pumps up again on next start.

With the rocker covers removed simply measure the height of the rocker arm above the gasket surface and compare to another cylinder, 4 vs 2 for example. Measure valve closed and compare to valve open height.

[Shadrach]

1 hour ago, A64Pilot said:

Cylinders with excessive wear, broken compression rings etc, do in fact lose compression and can do so to the point that they don’t even operate anymore, but before they get that bad, they lose power

In fact the big corn cob radials of old it wasn’t uncommon to fly aircraft with dead cylinders, from a loss of compression.

You can believe it’s a myth, but worn engines do lose power.

However leak down tests are not really a very good way to determine wear or ring seating, why? it’s because 80 PSI when compared to running cylinder pressures is trivial, and often simply isn’t enough to blow the rings out to make a good seal, so an engine with very low compression when tested with a leak down tester may not in fact have a lot of blow-by and compression loss when running, but if it does have excessive blow-by it does in fact have a loss of compression and lower compression does decrease power output.

But we aren’t talking lack of power here but a cylinder that peaks 100f higher than the others, other than ignition or compression I can’t come up with a reason it peaks higher can you?

I think it unlikely it has a wrong piston or a cylinder that the combustion chamber is so much larger than the others, possible, but unlikely. A leaking valve could reduce compression, or one not opening enough to completely fill the cylinder could.

He has ruled out plugs, incorrect fuel flow from his fuel flow test, although I can’t see how an improper injector could increase peak and he’s ruled out plugs although I’d rotate them anyway just to verify, easy and no money involved.

So other than compression and ignition, what else increases the temp at which a cylinder peaks? He also eliminated a bad probe by swapping probes and I don’t remember but assume they are all equidistant 

 

 

I too am perplexed. This is why I asked him for raw EGT numbers as well as verification that cylinder’s baseline full rich mixture setting against peak. The max EGT for an IO360 with stock cylinders is typically in the mid 1400 to mid 1500s.. He has a cylinde peaking in the high 1600s. That typically occurs with a single point of ignition. However, typically an engine with part of the ignition system dropping out peaks sooner than the rest, not later.

[lithium366]

I just did another flight after rotating fuel nozzles (they all filled cups the same). As expected - no changes in EGT / GAMI spreads but wanted to share some data:

Here is what I did with full rich mixture, 2600RPM at 4500ft:
12:15 set MP to 15

13:30 set MP to WOT (25.2)

this was done to test for an induction leak. I would expect #4 EGT to go up, not down when power is decreased

 

Then I climbed to 6500 and leaned to -60LOP with WOT of 23.1. GAMI spread was 0.8. This can be seen around 21:00 
Then I reduced power to 18MAP and repeated leaning procedure - see 23:30. GAMI spread is better - 0.6

[Shadrach]

At anytime did you check the mags in flight? 

[lithium366]

4 minutes ago, Shadrach said:

At anytime did you check the mags in flight? 

I did. Not sure how to link a previous message but I posted earlier in a thread Savvy profile with 3 leanings followed by mag check

Edited April 27, 2023 by lithium366