Request borescope interpretation

[RVSpike]

I recently started my 29th Condition Inspection on my RV-4 and found interesting images while bore scoping cylinder # 3. These radial lines are present all around except for the lower quarter where normal crosshatching is found. They stop short of top of piston travel.
Oil consumption is 1 quart in 7 or 8 hours and compression is mid 70s except for number 3 which is 66/80. I’m suspecting a broken oil control ring, but there has been no change in oil consumption and the combustion chamber isn’t particularly oily. The parallel O-360 A1A has only 172 hours SMOH on new cylinders. I hesitate to pull a cylinder if not necessary. Has anyone seen this condition before and is it something to be concerned about? Any insight is appreciated. I apologize for image quality. They are iPhone pictures of my borescope screen.

 

[avrojockey]

I just had something similar (search my posts). Don't know what caused it, but the barrel has overheated causing a wave effect matching the outside fins. The overheating can be external (airflow problems) or internal (loss of crosshatch to carry oil and ring friction on barrel.

You'll probably need to pull cylinder, inspect (dimensionally), hone, and re-ring if in spec. Mine looked way worse, with a lot of wear, and the cylinder was still good (STD) when Poplar Grove IRANed the cylinder.

 

[Dan 57]

For an engine that young the oil consumption is on the high side.
Now re your doubts... since compression on the cylinder #3 is on the low side, I'd suggest to first find out why. Applying air into that cylinder and finding as to where the air escapes will give you a clue. Air escaping thru the breather might then indicate a problem with one or more rings.
Do the other cylinders display similar patterns? Reason to ask is that most borescope seem to accentuate patterns as seen, and make pictures sometimes difficult to interpret.

 

[Jetmart]

What was the compression on #3 last time it was checked?
As suggested below I would try to determine where it is leaking.
At a minimum I would fly it some more and repeat the compression test. Mike Bush has some thoughts on this.
Did you send out oil analysis and does it show anything.
Prior to pulling I would get 2nd and 3rd opinions from qualified individuals. Not from forums. Perhaps Savvy Aviation.
I would not be in a rush to pull the cylinder.

 

[Majorpayne317641]

Piston ring flutter. I’ve seen it on high boost automotive engines when the rings get too hot and the gaps are not big enough for the piston ring to expand in the bore. Not sure if that’s the same issue here but it does look like your piston rings are “fluttering” in the bore. It won’t get better with time, are the cylinders run hot at all?

 

[OKAV8r]

Piston ring flutter. I’ve seen it on high boost automotive engines when the rings get too hot and the gaps are not big enough for the piston ring to expand in the bore. Not sure if that’s the same issue here but it does look like your piston rings are “fluttering” in the bore. It won’t get better with time, are the cylinders run hot at all?

Agree as far as to ring flutter, but I have to wonder if the compression rings got installed upside down? Or, maybe the overhaul re-used old pistons? Worn ring lands (grooves) can cause flutter.
I'd pull it, it won't get better. Hone the jug, check the piston very carefully for correct dimensions, (or just replace it), and install new rings.

 

[RVSpike]

I appreciate all of your responses. I rechecked the cylinder pressure today in the cold condition and now it’s 58/80 and the air is clearly escaping from the dipstick tube, indicating a piston ring issue.
Only the #3 cylinder exhibits “chatter marks” and it looked good last CI. I sent out the oil analysis sample today. The oil filter and oil screen were both super clean after 47 hours since last oil service.
Additional photos show the chatter marks transitioning to normal crosshatch along the bottom of bore. Would ring flutter only exhibit part way around the cylinder bore?
Knowing this condition will not fix itself, I’m bracing for pulling the cylinder, but will hold off until I receive new rings and get some additional expert feedback.

 

[johnpaul44]

Are these superior cylinders and superior rings by chance ?

 

[RVSpike]

Are these superior cylinders and superior rings by chance ?

I believe these are ECI assemblies originally installed by Mattituck 24 years ago. The engine sat in the crate in a “climate controlled environment “ for 23 years.

 

[johnpaul44]

I believe these are ECI assemblies originally installed by Mattituck 24 years ago. The engine sat in the crate in a “climate controlled environment “ for 23 years.

I had exact same pattern on some superior cylinders, a rehone and switch to Lycoming fixed the issue. Superior took care of me . My advice would be to pull that cylinder and see about a rehone and re ring . I believe this pattern can be caused by incorrect hone crosshatch angle

 

[swift12]

Forget compression checks and do a leak down test. Way more reliable. Can tell wether it’s valves or rings too.

 

[[email protected]]

I have the same problem since new on Superior Cylinders installed on an IO540, compressions were still in mid 70s at 100 hrs. I did reach out to superior but did not receive a response. Now that I see others having this same issue I will reach out again.

 

[avrojockey]

I believe these are ECI assemblies originally installed by Mattituck 24 years ago. The engine sat in the crate in a “climate controlled environment “ for 23 years.

Coincidently...my similar issue was with an ECI cylinder. About 40 hrs after the hone and re-ring and that jug is fine now. Pretty easy fix