What Happened to this Cylinder?

[avrojockey]

Overhauled O320-E2D (with 8.5:1 pistons)
ECI Cylinders AEL65102 non-AD cylinders

Found wavy wear region during borescope of #4 Cylinder when Blackstone called me to tell me my chrome is way too high (110 ppm, should be single digits). Engine was running great producing good power with only 20 hrs on it. No metal in filter or screen when changed at 10 hrs of run time...though there was some very fine powdery steel caught on magnet which I assumed was from break-in.

When I first scoped it I assumed broken ring. Rings are not broke, but the wear on the rings is atypical. Side clearance on top land is out of spec (.009), but there was enough wear on the sides of that top compression ring that I couldn't see the laser etched part number anymore. Not sure if either of these is a symptom or a cause.

Poplar Grove did the IRAN with new hone and new rings, etc. The other cylinders seem fine but the compressions are really low (60s) with all air going past the rings on all cylinders. Break-in seemed to be great with all CHTs and oil consumption good, until the last 5-10 hrs the oil consumption started going up, presumably due to to this issue. CHTs were good but you can see the steel barrel was hot enough to discolor and bubble the paint on the outside.

Any idea what would cause the rings to wear the cylinder like that?? you can feel the waviness to the wear, couple that with overheating the barrel and I think the cylinder is trash.

These are the parts using in overhaul, supplied from Poplar Grove. From my research they are the correct rings. Although rocketbob show a different Superior set for steel than what Lycoming and Continental/Titan/ECI show

ECI AEL65102 IRAN
Ring Set 05K22035 - 74241(2), 14H21950(1)

 

[gasman]

Not enough ring gap??

 

[avrojockey]

Not enough ring gap??

Gaps good…checked by poplar grove and rechecked by me.

 

[Ironflight]

I didn;t look up the part numbers….Are they Cerminil cylinders? Those need special rings - there are potential odd combinations…..

 

[BillL]

You definitely have ring flutter. That is what caused the wear. Maybe Mahlon will add to your knowledge. Only one side of the ring moved thus the sharp line on one side and fuzzy on the other to the wear region. The rings dont look like plasma faced rings. It could have been geometry of a defective ring or as Paul mentions, a ring face material mismatch with the bore. Poplar Grove usually knows what they are doing, but a good discussion with them definitely is in order as they should have spotted any issues up front.

Happy hunting for the root cause and solution.

edit - second look at photos - that appears to be a keystone ring, if it was installed in a rectangular groove that could be your root cause. The keystone would allow the ring to twist under pressure and friction thereby rolling the face against the bore from edge to edge. Very unhappy situation if that is right. Check ring and piston for this geometry. Were app 4 cylinders processed? You may have a larger problem.

 

[lr172]

You definitely have ring flutter. That is what caused the wear. Maybe Mahlon will add to your knowledge. Only one side of the ring moved thus the sharp line on one side and fuzzy on the other to the wear region. The rings dont look like plasma faced rings. It could have been geometry of a defective ring or as Paul mentions, a ring face material mismatch with the bore. Poplar Grove usually knows what they are doing, but a good discussion with them definitely is in order as they should have spotted any issues up front.

Happy hunting for the root cause and solution.

edit - second look at photos - that appears to be a keystone ring, if it was installed in a rectangular groove that could be your root cause. The keystone would allow the ring to twist under pressure and friction thereby rolling the face against the bore from edge to edge. Very unhappy situation if that is right. Check ring and piston for this geometry. Were app 4 cylinders processed? You may have a larger problem.

I agree with much of the above but have a different theory. That side wear on the ring is crazy bad for 20 hours and the amount of metal removed from the cyl wall is also A LOT for 20 hours (ALL of the cross hatch is gone). I am not sure ring flutter could wear away this much material in 20 hours (have never seen the results of flutter damage first hand, so no experience to offer). My guess is one ring land (the wide one you measured and the first clue) was improperly machined and the floor is out of round and for 1/4 of the piston circumference is to shallow to accommodate the ring depth; or possibly a burr or other machining artifact. This lack of clearance pushes the ring into the cly wall mechanically and creates a VERY rapid wear scenario. To me, the only way to scrape off that much metal in 20 Hours and produce enough heat to burn off the paint is this type of mechanical pressure. This scenario also explains the significant piston scuffing in only one discrete spot (and not just the skirt, but all the way to the very top) that is rarely seen that large, especially on a 20 hr engine. The inability of the ring to easilly move up and down along the wall is what creates all the wear on the ring side and ring land. You would see something similar in these areas when the ring gap is too small. But the piston scuffing shows us that is not the issue here, along with a cyl wall wear pattern that does not match that scenario.

Pretty easy to confirm or disprove. Put the good ring back on the bad land and try to press the ring into the land with a straight edge at various points around piston. Ring should be able to recess to at least flush with piston wall. If it doesn't and sticks out more than a couple thou, that is the problem. The flaw in the land should be exactly opposite of the scuff marks. Do NOT use the worn ring as it may have already eaten several thou off the ring. You can alsu use the depth side of a caliper to measure the land depth.

I feel for you and the seemingly unending run of bad luck you are having. To save that cyl, you will likely need to bore it 10 over. likely not trashed, but not sure you want to mis-match cyl bores. I would ask poplar what they think of that. This pison in this cyl would have been dragging a good bit harder than all of the others and kind of think they should have caught it during assembly.

Larry

 

[avrojockey]

I didn;t look up the part numbers….Are they Cerminil cylinders? Those need special rings - there are potential odd combinations…..

Cylinder is ECI steel AEL65102 ST 04.1

Ring set was Lycoming 05K22035 which include chrome rings. ECI/Continental ring set calls for a slightly different shaped ring in #2 compression but also specify a Superior equivalent (non- plasma) which has the same shaped compression rings as the Lycoming set installed. Poplar Grove said any of them are adequate. They also said the wavy pattern is most likely caused by the uneven heat of the steel from the barrel fins...a quick look at the pattern compared to the exterior fins match that theory. They're going to take a look at the cylinder and see if tis salvageable, but with provide a core if not. They will make it right

 

[avrojockey]

You definitely have ring flutter. That is what caused the wear. Maybe Mahlon will add to your knowledge. Only one side of the ring moved thus the sharp line on one side and fuzzy on the other to the wear region. The rings dont look like plasma faced rings. It could have been geometry of a defective ring or as Paul mentions, a ring face material mismatch with the bore. Poplar Grove usually knows what they are doing, but a good discussion with them definitely is in order as they should have spotted any issues up front.

Happy hunting for the root cause and solution.

edit - second look at photos - that appears to be a keystone ring, if it was installed in a rectangular groove that could be your root cause. The keystone would allow the ring to twist under pressure and friction thereby rolling the face against the bore from edge to edge. Very unhappy situation if that is right. Check ring and piston for this geometry. Were app 4 cylinders processed? You may have a larger problem.

Steel bore, attached are the rings specified by ECI/Continental:

You can see the top ring is plasma faced version of 74241, which is what was installed. The second compression ring in set is different, but the Superior set SL3601-SC has the same ring for top and bottom compression.

To reiterate, here is what was installed as Lycoming ring set 05K22035:
Top compression - 74241
Bottom Compression - 74241
Oil - 14H21950

All 4 cylinders were IRAN'ed and assembled with same ring set. I don't know if this points to the other issue of low compression on cylinders, leaking past rings, even after 20 hrs of break in.

 

[mahlon_r]

Cylinder wash boarding is normally caused by heat. Birds nest between the cylinders? Improper intercylinder baffle or regular baffle installation? The text of ECI sb 93-6-7 is below. Maybe operational cause if the parts all check out.
Good Luck, Mahlon
Proper leaning is essential to efficient operation of aircraft piston engines. Much has been written about the
technique for establishing the optimum lean operating conditions, but not much has been written about the effects
of rapid leaning. A recent occurrence in an engine test being performed by Engine Components, Inc. (ECi) to show
the compliance with the regulations regarding detonation has caused us to reconsider the danger of rapid leaning.
During the test, an engine was rapidly leaned from a rich cruise power setting in an attempt to create conditions for
detonation. The engine Coughed, and a brief flame was observed coming from the exhaust. However, an engine
analyzer was being used, and no detonation was observed on the scope. An immediate tear down revealed that the
pistons overheated and were scuffed around the skirt. There was no evidence of detonation. Additionally, the
cylinder bores appeared glazed, and two cylinders had ripple (washboard) patterns in the bore corresponding to the
location of the cooling fins around the barrel.
Evaluation of the test and results has convinced ECi that the cause for the scuffing and washboard effect is the rapid
heat influx due to leaning could not be dissipated by the piston, but the barrel remained relatively cool due to
airflow. The piston expanded due to heat, and the loss of side clearance caused further heating. In two cylinders, the
piston expanded so fast that the pressures on the bore deformed the barrel between cooling fins.
Glazed and washboard cylinder barrel bores have been observed over the years by personnel at ECi, but
the cause was usually attributed to break-in problems or shock cooling. It is now confirmed that shock
heating can also create the anomaly. The cylinders in the engine test described above were confirmed to
have been broken-in properly, and had even been checked with a bore scope just prior to the rapid leaning
incident. ECi personnel are convinced that this phenomena can be produced in any engine that is leaned
too rapidly.
The use of a fuel flow meter to rapidly establish preliminary mixture settings can lead to the anomaly
described. In fact, many of the cylinders found with the characteristics described above are from the type
of airplanes that often have fuel flow meters. ECi recommends that the following note be added to
operating instructions:
CAUTION
LEANING OF THE MIXTURE SHOULD ALWAYS BE ACCOMPLISHED SLOWLY TO ALLOW
CYLINDER TEMPERATURES TO STABILIZE. RAPID LEANING CAN CAUSE LOSS OF PISTON TO
BORE CLEARANCE THAT CAN CAUSE PISTON SCUFFING AND BARREL DAMAGE.

 

[KiloWhiskey1]

CAUTION
LEANING OF THE MIXTURE SHOULD ALWAYS BE ACCOMPLISHED SLOWLY TO ALLOW
CYLINDER TEMPERATURES TO STABILIZE. RAPID LEANING CAN CAUSE LOSS OF PISTON TO
BORE CLEARANCE THAT CAN CAUSE PISTON SCUFFING AND BARREL DAMAGE.

Any guidance on how slowly? SAVVY’s test profile suggests no less than 3-4 minutes from rich to lean roughness. Airflow Performance’s GAMI nozzle test card suggests 0.2gph adjustments and then let temps stabilize between mixture changes. These are data collection tests, so probably slower than practical for normal operations.

 

[DanH]

Here we see the washboard pattern on the intake side of the cylinder. Was the washboard pattern also evident on the exhaust side?

At TDC, does the pattern extend to the top ring's stop and go location, or into the area above it?

These are data collection tests...

Exactly, so each data point has an opportunity to stabilize. Nothing to do with operational leaning.

Probably a bit more to this than simply "piston expanded before the cylinder".

 

[avrojockey]

Cylinder wash boarding is normally caused by heat. Birds nest between the cylinders? Improper intercylinder baffle or regular baffle installation? The text of ECI sb 93-6-7 is below. Maybe operational cause if the parts all check out.
Good Luck, Mahlon
Proper leaning is essential to efficient operation of aircraft piston engines. Much has been written about the
technique for establishing the optimum lean operating conditions, but not much has been written about the effects
of rapid leaning. A recent occurrence in an engine test being performed by Engine Components, Inc. (ECi) to show
the compliance with the regulations regarding detonation has caused us to reconsider the danger of rapid leaning.
During the test, an engine was rapidly leaned from a rich cruise power setting in an attempt to create conditions for
detonation. The engine Coughed, and a brief flame was observed coming from the exhaust. However, an engine
analyzer was being used, and no detonation was observed on the scope. An immediate tear down revealed that the
pistons overheated and were scuffed around the skirt. There was no evidence of detonation. Additionally, the
cylinder bores appeared glazed, and two cylinders had ripple (washboard) patterns in the bore corresponding to the
location of the cooling fins around the barrel.
Evaluation of the test and results has convinced ECi that the cause for the scuffing and washboard effect is the rapid
heat influx due to leaning could not be dissipated by the piston, but the barrel remained relatively cool due to
airflow. The piston expanded due to heat, and the loss of side clearance caused further heating. In two cylinders, the
piston expanded so fast that the pressures on the bore deformed the barrel between cooling fins.
Glazed and washboard cylinder barrel bores have been observed over the years by personnel at ECi, but
the cause was usually attributed to break-in problems or shock cooling. It is now confirmed that shock
heating can also create the anomaly. The cylinders in the engine test described above were confirmed to
have been broken-in properly, and had even been checked with a bore scope just prior to the rapid leaning
incident. ECi personnel are convinced that this phenomena can be produced in any engine that is leaned
too rapidly.
The use of a fuel flow meter to rapidly establish preliminary mixture settings can lead to the anomaly
described. In fact, many of the cylinders found with the characteristics described above are from the type
of airplanes that often have fuel flow meters. ECi recommends that the following note be added to
operating instructions:
CAUTION
LEANING OF THE MIXTURE SHOULD ALWAYS BE ACCOMPLISHED SLOWLY TO ALLOW
CYLINDER TEMPERATURES TO STABILIZE. RAPID LEANING CAN CAUSE LOSS OF PISTON TO
BORE CLEARANCE THAT CAN CAUSE PISTON SCUFFING AND BARREL DAMAGE.

The ECI article is interesting, though my leaning technique hasn't change from before the engine overhaul and there was no piston scuffing and barrel damage noted during teardown that I know of. I'll talk to Bryan at Poplar.

I lean a little gradually during climb out, and cruise I pull a little more till RPM drops slightly, let it stabilize for a minute then veneer a little more to LOP. This was my technique after I thought the cylinder was broken in. Leaned to max power before that.

Bryan at Poplar said the same thing about the washboarding...but there was not any obstruction to air flow and inter cylinder baffles installed correctly. The only obstruction is the wire run for starter and alternator below and that's been there per Van's for the life of the aircraft.

 

[avrojockey]

Here we see the washboard pattern on the intake side of the cylinder. Was the washboard pattern also evident on the exhaust side?

At TDC, does the pattern extend to the top ring's stop and go location, or into the area above it?

Pattern is only on the intake side, nothing on the exhaust. I don't have the cylinder anymore but from the pictures it looks like it stops at top of ring travel.

 

[Mikeyb]

So confused
I used to slowly lean from full rich like the lycoming operator manual says. Then I read an article on the internet that said don’t do that. Lean quickly. Now another warning to do it real slow.

 

[Freemasm]

A bit hard to believe, to me at least. When components and associated clearances are designed to survive the brutal transients associated with start-up, run-up, etc. it's hard to conceive that the leaning process would cause the subject damage.

Starts, power-off/low power decents/etc decrease parts life, but rapid leaning causes damage to the point that necessitates cylinder replacement?

I've been wrong my share of times but I just can't buy the ECI's rapid leaning causation here. As of now, my skeptical nature has me thinking the release was an excuse for a design or manufacturing quality issue. Would be interesting to know if the ECI piston and/or ring designs were changed after their associated findings were discovered.

 

[DanH]

Let's not highjack Tim's issue...which isn't leaning.

Pattern is only on the intake side, nothing on the exhaust. I don't have the cylinder anymore but from the pictures it looks like it stops at top of ring travel.

Ok. Read Bill's words again...

Only one side of the ring moved thus the sharp line on one side and fuzzy on the other in the wear region.

The game is to determine why.

 

[avrojockey]

I'm pretty confidant we can rule out an exterior heat root cause (obstruction, birds nest, shock cooling).

I would tend to think the piston scuffing was a symptom rather than the cause in the case of shock cooling/overheating. Bill and Larry seem to going the right direction. All rings were completely free when removed and moved radially(?). I think carbon buildup in the land is excessive for 20 hrs but could certainly be a symptom also.

Miss my airplane already...I hate driving to work

 

[avrojockey]

Couple updates:

Poplar Grove was able to re-hone barrel and stay standard Fantastic service from them BTW! Super nice having them close and being able to overnight via UPS ground.

When I removed cylinder and measured ring land side clearance is was out of spec (.009). After receiving cylinders and piston back from Poplar with new rings and same piston, the wear in top land seems to be partially ring and piston...side clearance with new ring set is .003 which is in limits but less than .0015 clearance of the next ring land.

Still don't know what caused this, but gave Bryan at Poplar all the data they requested and haven't heard their opinion yet. The overheat issue was definitely created internally as my baffling and cooling is good. Heat never translated to head as highest CHT was 390 airborne, 300 ground, after overhaul.

We will see if issue gets fixed...the only thing different this time is the ring set, I'm using Superior as a alternative called out by TCM docs...Lycoming equivalent rings were used by Poplar before.