Glazed Cylinder Borescope Images

[TheAv8r]

4 minutes ago, EricJ said:

That's not bad, especially if it's consistent.    I think it took mine a hundred hours or two before it settled down.    It's been 6-7 hours/qt since then, which is pretty typical, so you're not far off.

 

It is consistent! I've done XCs, local flights, 1hr, 2hr... keeps getting back to that number. I always thought somewhere around 8-12hrs/qt was the norm though, 5hrs feels high. My old engine was 8hrs/qt at 1800hrs SMOH. The last Mooney I owned before it was 15-20hrs/qt on 500hrs SMOH. Maybe it will settle down in a year or two, I just am tired of flying it at 75% power, I like to run 65% power LOP on XCs to save gas. Plus I'm ready to cruise up at the higher altitudes and not stay below 5500...

[EricJ]

1 minute ago, TheAv8r said:

It is consistent! I've done XCs, local flights, 1hr, 2hr... keeps getting back to that number. I always thought somewhere around 8-12hrs/qt was the norm though, 5hrs feels high. My old engine was 8hrs/qt at 1800hrs SMOH. The last Mooney I owned before it was 15-20hrs/qt on 500hrs SMOH. Maybe it will settle down in a year or two, I just am tired of flying it at 75% power, I like to run 65% power LOP on XCs to save gas. Plus I'm ready to cruise up at the higher altitudes and not stay below 5500...

If it's been consistent there's probably just a little more wear to happen to fully seat the rings, since it only has 48 hours on it.  I'd suggest just flying it the way you want to fly it and see what it does.   If it doesn't get worse, you're golden, as it'll probably just get a bit better with time.

And, yes, 5-8 hours/qt is pretty typical for 4-cyl Lycomings. The ones that do better are exceptional, and 15-20 hrs/qt is especially exceptional.    That's low enough I'd be worried about something being too weird in there.   

[TheAv8r]

Update here - 

We did a compression check and all 4 cylinders were 80/80. No air was escaping or could be heard. 

We then borescoped the cylinders and did find a few anomalies. I have sent these over to the shop to get their thoughts, but here are they are down below for the hivemind . 

Dark streaks down the bottom of one of the cylinder - A&P noted it did not seem to be cutting into the metal. That burnished splotch on the top is wet oil, not glazing, after looking at a few different angles per my A&P. 

More streaks/scrapes on one of the cylinders towards the end of travel near the valves. 

At 80/80 compression, I have a hard time understanding mechanically how the rings aren't seated, as that kind of compression means nothing is escaping past the rings, which indicates they are flush against the cylinder wall right?

We'll see what we hear back from the shop.

[EricJ]

11 minutes ago, TheAv8r said:

Update here - 

We did a compression check and all 4 cylinders were 80/80. No air was escaping or could be heard. 

We then borescoped the cylinders and did find a few anomalies. I have sent these over to the shop to get their thoughts, but here are they are down below for the hivemind . 

Dark streaks down the bottom of one of the cylinder - A&P noted it did not seem to be cutting into the metal. That burnished splotch on the top is wet oil, not glazing, after looking at a few different angles per my A&P. 

More streaks/scrapes on one of the cylinders towards the end of travel near the valves. 

At 80/80 compression, I have a hard time understanding mechanically how the rings aren't seated, as that kind of compression means nothing is escaping past the rings, which indicates they are flush against the cylinder wall right?

We'll see what we hear back from the shop.

You can still see the cross-hatching through those streaks, so they don't appear to be very deep at all.   If your compression is good and the valves look good I'd leave it until the next inspection and see if it is gone or gotten worse.

[PT20J]

80/80 is kind of hard to get because there should be gaps in the rings. An old auto maintenance trick to determine if the rings are leaking is to squirt oil in the cylinders and see if the compression improves because the oil seals the rings. I might try letting the engine sit a day or so and then do a cold compression test. We did a lot of cold compression tests at the museum because it was a lot of work to tug several large aircraft out of the hangar to get one out on the ramp to run it. If the compression was low, we'd repeat the test hot. We never noticed much difference cold compared to hot on a good jug.

At the Lycoming factory school they said not to be concerned with scratches in the cylinder walls if you can see the cross hatch through them. The leak down compression test mainly tests rings and valves. To check cylinder condition, the instructor suggested doing an automotive style pressure test because the piston travels the entire length of the cylinder to generate the pressure. For an IO-360 the quoted pressures were 155 psi (new), 140 psi (mid-life) and 120 psi (worn out).

 

[EricJ]

1 hour ago, PT20J said:

80/80 is kind of hard to get because there should be gaps in the rings. An old auto maintenance trick to determine if the rings are leaking is to squirt oil in the cylinders and see if the compression improves because the oil seals the rings. I might try letting the engine sit a day or so and then do a cold compression test. We did a lot of cold compression tests at the museum because it was a lot of work to tug several large aircraft out of the hangar to get one out on the ramp to run it. If the compression was low, we'd repeat the test hot. We never noticed much difference cold compared to hot on a good jug.

At the Lycoming factory school they said not to be concerned with scratches in the cylinder walls if you can see the cross hatch through them. The leak down compression test mainly tests rings and valves. To check cylinder condition, the instructor suggested doing an automotive style pressure test because the piston travels the entire length of the cylinder to generate the pressure. For an IO-360 the quoted pressures were 155 psi (new), 140 psi (mid-life) and 120 psi (worn out).

 

Even better is a dynamic compression test, but I don't know if those are really available for our engines or not.    They're pretty common in advanced automotive test equipment, where a pressure transducer in the spark plug hole monitors cylinder pressure while it gets turned over by the starter.   The shape of the pressure rise and fall characteristic through the various strokes can be revealing for various ailments.    What we do on these engines is pretty primitive in comparison.

[Shadrach]

 

7 hours ago, PT20J said:

80/80 is kind of hard to get because there should be gaps in the rings. An old auto maintenance trick to determine if the rings are leaking is to squirt oil in the cylinders and see if the compression improves because the oil seals the rings. I might try letting the engine sit a day or so and then do a cold compression test. We did a lot of cold compression tests at the museum because it was a lot of work to tug several large aircraft out of the hangar to get one out on the ramp to run it. If the compression was low, we'd repeat the test hot. We never noticed much difference cold compared to hot on a good jug.

At the Lycoming factory school they said not to be concerned with scratches in the cylinder walls if you can see the cross hatch through them. The leak down compression test mainly tests rings and valves. To check cylinder condition, the instructor suggested doing an automotive style pressure test because the piston travels the entire length of the cylinder to generate the pressure. For an IO-360 the quoted pressures were 155 psi (new), 140 psi (mid-life) and 120 psi (worn out).

 

Cold compression checks are the norm for us at annual given that when my IA arrives the plane has typically been on jacks for a day or two with panels removed.  I have never noticed much difference between cold and hot. That being said we have gotten compressions of 80/80 on several occasions. A few years ago we got the trifecta on a cold engine that had not run in 6 weeks. Next year, none of them were 80/80 but all were above 77.
I put no stock in such things… 80/80 compressions are good for little more than bragging rights on an Internet forum.

[GIIIPilot]

Here is an update. I took the cylinders off, got them rehoned and reinstalled. Dialed in the idle and mixture. On flight testing I still have poor climb performance and cruise. I talked to local mechanics, Savvy Aviation, Lycoming, Airflow Performance, Hartzell and have run through various air and ground trouble shooting schemes.

I think I found the smoking gun! I performed a valve timing check in the Lycoming Trouble Shooting Guide (SSP-475) that basically says check if the cylinder #2 intake valve begins to open and the exhaust valve begins to close as cylinder #1 passes TDC on its compression stroke. The opening and closing on my engine occurred at about 23 deg before TDC.

I opened the accessory housing and found that the idler gear markings were correctly aligned to the cam and crank gears per Lycoming Overhaul Manual (p/n 60294-7) paragraph 7-101 and figure 2-8. Or so I thought. I was looking at the markings on the face of the double gear which turns out to be the magneto marking and some extraneous blemish. I found the actual cam/crank markings in the grove between the two gears. Once the proper marking are aligned the conditions of SSP-475 are satisfied.

Besides the oil in the cylinders, I was seeing climb and cruise numbers that could only be explained by reduced power. I also had low CHTs. In any condition of flight CHTs would not go above 350 deg F. Good right? Not so! In my mind the valve timing issue explains the cooler CHTs (exhaust valve opening well into the power stroke) and the oil in the cylinders (both valves closed while the piston is still pulling a vacuum at the end of the intake stroke).  

In the coming weeks I will reassemble my engine and take it for a ride. I will let you know the outcome.

Edited December 3 by GIIIPilot