Had A&Ps replace intake gaskets and borescope

[phxcobraz]

I am working in South Dakota for a little over a month before I drop my M20C off at WeepNoMore. Decided since my bird is sitting on the ramp here I might as well have the guys take care of a few things. I noticed blue staining on the intake tube flange and a very occasional lean cyl(1, 2, or 4), so asked them to replace the gaskets. Since they were in there I figured we might as well do a borescope to see if anything stands out. Last 2 annual mechanic didn't do one and been trying to diagnose oil on the belly and about 1qt every 5-6hrs.

He found quite a bit of blue buildup in the intake runner from the carb(see pic), hopefully the gaskets sort this out.

 

Attached are the other cyl pics. There is some pooling of oil in cyl 1 and 2. Which makes me think bad rings, thus case pressure. All compressions were 76+/80 at annual in March but I wonder if the oil was interfering. The lower plugs were clean at annual. About 450smoh, but previous owner didn't fly it a whole lot after he did the overhaul(maybe 30hrs/yr for 10yrs). (I am not an engine guy, I just read a lot lol). It gets darker by about 20hrs after oil change.

Otherwise the engine runs fantastic, starts very easy, idles great, leans well and doesn't struggle with high CHTs in climb, even in AZ.

The guys on the field here said they don't do much engine work, and to find someone more specialized.

Any ideas about next steps? Perhaps pull Cyl 1 and 2? Replace rings? Do nothing since the plane is fine and keep up with oil? It will be at WeepNoMore after this for about 1month so have time to decide.

Down Cyl1

Down C2

Down C3

Down C4

C2 Piston

ex cyl 1

ex cyl 2

ex cyl 3

ex cyl 4

In C1

In C1 seat

In C2

In C3

In Cyl 4

Oil in Cyl 1

Oil in Cyl 2

Cyl 1 Up

Cyl2 Up

Cyl 3 Up

Cyl 4 Up

Edited May 31, 2023 by phxcobraz

[Vance Harral]

My understanding (I am not an engine mechanic) is that the presence of a small amount of pooled oil on the cylinder walls above the piston during a borescope inspection, doesn't necessarily indicate anything about the rings.

Lycomings lubricate their rocker arms and valve stems by spray action through the pushrods.  So any time the engine shuts down, there's going to be a bunch of oil in that area.  As the engine cools, most of this drains down the hole in the head assembly that connects to the infamous drainback tubes (that themselves are sometimes sources of oil leaks).  However, if either the intake or exhaust valve of a cylinder happens to stop in the open position - which I think is always the case in at least one cylinder - some of that oil can wick along the valve and dribble into the cylinder instead of going down the drainback tube.  That seems to me to be the most likely explanation for what you're seeing.

If your rings are bad, and the crankcase is getting pressurized, it can blow oil up into the combustion chamber.  But that oil is going to almost instantly get burned during the next combustion event.  I don't think that scenario results in carmel-colored oil on the cylinder walls as seems to be shown in your photos.  I'd expect to see carbonized residue instead.

Again, I'm not an engine mechanic, and defer to others more knowledgeable.  But my initial take is that this is not something to worry about.

 

[A64Pilot]

A quart every five hours or so is fine.

From what I see it does look like you have some corrosion pitting, but with compressions at worst at 76 and without oil fouling plugs I’d advise putting cylinder money into Avgas and enjoy flying. It’s likely over time your oil consumption will improve some. You’ll know when it’s time when you begin oil fouling plugs and she will lose some power.

Ideal world you would buy new cylinders, I’d start saving knowing it’s in your future but for now I’d keep flying.

It’s real easy to spend so much that there isn’t enough left in the budget to fly.

[Jsno]

That is the trouble with steel cylinders, they will rust and pit if not flown often.  I have had this happen with new cylinders within a few weeks.  It will cause some blobby making the oil dirty earlier.  It will leave more oil on the cylinder walls causing oil to accumulate.  You can fly it like this a long time.  Many cylinders have this condition without the owner knowing.  The borescope makes it appear worse than it is.  The only cure is to have the cylinders plated.  I use Nikel as they break in within an hour of flying and you do not have to worry about corrosion anymore.  Fly it and enjoy and maybe one day do a top overhaul with plated cylinders.

[phxcobraz]

1 hour ago, A64Pilot said:

A quart every five hours or so is fine.

From what I see it does look like you have some corrosion pitting, but with compressions at worst at 76 and without oil fouling plugs I’d advise putting cylinder money into Avgas and enjoy flying. It’s likely over time your oil consumption will improve some. You’ll know when it’s time when you begin oil fouling plugs and she will lose some power.

Ideal world you would buy new cylinders, I’d start saving knowing it’s in your future but for now I’d keep flying.

It’s real easy to spend so much that there isn’t enough left in the budget to fly.

That’s kind of what the shop here said. They are mainly a flight school and charter shop and the IA said they would just keep running it and pay more attention to those items at at 100hr/annual to make sure nothing is changed. I do oil analysis at every oil change and it’s been great. 

[PT20J]

The pictures are kind of blurry, but a couple of them look like chromed cylinders. Are you sure you have steel cylinders? Chrome cylinders will be marked with orange paint on the cooling fins near the top spark plug or on the cylinder base. Chromed cylinders generally burn more oil. But regardless, 5 hrs/qt isn’t abnormal and I wouldn’t worry about it unless it changes suddenly. Oil is cheaper than top overhauls. 

[MB65E]

I would agree that a few of the cylinders look chromed to me as well. 
That said, everything looks great to me.

-Matt

[phxcobraz]

Thanks for having a look folks, I always tell people Mooneyspace is the best collection of people to help you decide what to do when a mechanic doesn't have a definitive answer. I love it when people say just fly it!

I will go pull the cowling off later today @PT20J and check if there is orange paint on the cooling fins. I kinda feel like I saw that before, but I never knew that is what that meant.

[EricJ]

Here's the color code decoder for Lycoming cylinders.    In rare cases there is also a color code near the top spark plug if the cylinder is configured for long-reach spark plugs.

https://www.lycoming.com/content/understanding-engine-color-codes

[Mcstealth]

16 hours ago, Jsno said:

.  It will cause some blobby......

"What in the Wide wide World of Sports"  is blobby?

 

Name that Movie

[Greg Ellis]

2 hours ago, Mcstealth said:

"What in the Wide wide World of Sports"  is blobby?

 

Name that Movie

Blazing Saddles

[Yetti]

fly it.   Oil in the cylinders will increase compression checks.

I have a new cylinder in the box.    We thought we would need it, but field OH 2 cylinders that were still in spec.   Been flying it for 5 years.   The cylinder in the box has gone up in value.

[phxcobraz]

Checked it out. Yep orange stripes on the cylinders, so makes sense why the look chrome, they are!

 

[A64Pilot]

16 hours ago, Yetti said:

fly it.   Oil in the cylinders will increase compression checks.

I have a new cylinder in the box.    We thought we would need it, but field OH 2 cylinders that were still in spec.   Been flying it for 5 years.   The cylinder in the box has gone up in value.

Be sure to inspect it and put some kind of corrosion preventative on it, and put it in a large zip loc bag with a bag of desiccant.

I knew someone who bought a crankshaft from Lycoming for the AD when Lycoming sold them at a discount, AD specified replacement at overhaul so he put it aside, when overhaul came he opened it up to find excessive corrosion, second crankshaft he had to pay full price.

[A64Pilot]

15 hours ago, phxcobraz said:

Checked it out. Yep orange stripes on the cylinders, so makes sense why the look chrome, they are!

 

If chrome, unlikely they have corrosion, chrome doesn’t seal well and high oil consumption is normal, chrome is very hard and suffers very little from wear, usually the end of a chrome cylinder is when the chrome begins flaking off, if you do oil analysis that should tell you when that happens.

Chrome is mostly gone for several reasons, the new plating on the block is different forms of Nickel plating, which has been used successfully for years in especially the motorcycle industry, but then so was chrome.

Nikaseal, Cermichrome, and other variations of Nickel may prove to be very superior to plain steel. One thing it’s additional price is pretty minimal so price isn’t a reason to not go with it.

I personally would not replace them with chrome 

[Jsno]

On 6/1/2023 at 11:36 AM, Mcstealth said:

"What in the Wide wide World of Sports"  is blobby?

 

Name that Movie

blobby

[Fly Boomer]

2 hours ago, Jsno said:

blobby

???

[phxcobraz]

On 6/2/2023 at 1:16 PM, Fly Boomer said:

???

Just to confirm, I am as confused as you are, perhaps a hyper local dialect?

[phxcobraz]

Trend stays tracking. Flew a couple local flights and went to KMIC this weekend for a concert, came back Sunday. 
almost exactly 5.1hrs on the Hobbs and it is down 1qt. 
Leaning and egt was significantly more consistent across cylinders after replacing the intake gaskets. 

[A64Pilot]

1 gt for 5 hours on chrome cylinders is within spec in my opinion, keep an eye on compressions though and if you do oil analysis on chrome.

If or when it begins to flake off your compression check on that cylinder will tank, you could fly for hundreds of hours and years though without a problem

Downside to chrome is that they use a lot of oil

[cliffy]

Lycoming says at  about 3/4 of a quart per hour and its time to pull them. Yes. 3/4 quart per hour oil burn. 

[A64Pilot]

21 hours ago, cliffy said:

Lycoming says at  about 3/4 of a quart per hour and its time to pull them. Yes. 3/4 quart per hour oil burn. 

The formula is here, but I don’t know why they didn’t just give a number to multiply by HP for the math challenged. https://www.lycoming.com/sites/default/files/attachments/Lycoming%20Reciprocating%20engine%20Break-In%20and%20Oil%20Consumption.pdf

Although here https://www.lycoming.com/content/tips-hangar

you will find this answer

QUESTION: At what rate of oil consumption does continued operation of the engine become a hazard? ANSWER: Generally speaking, when the oil consumption reaches one quart per hour, corrective action should be taken. However, maximum permissible for each particular engine is listed in the engine operator’s manual.

Seems to me that they aren’t real worried too much about oil consumption.

[A64Pilot]

I just got to thinking, a two stroke typically if pre-mix burns a fuel to oil ratio of 50 to 1.

An aircraft engine burning one quart of oil an hour if burning 10 GPH of fuel is burning oil at 40 to 1, much more than a two stroke.

Someone tell that to the Friends of the Earth  

[cliffy]

SHHHHHHH!!!!

You can run out of oil before you run out of gas if the oil is low!!!!!

 

IIRC min for the certification run was 2 1/2 qts. 

Edited June 7, 2023 by cliffy
add

[Jsno]

On 6/1/2023 at 11:36 AM, Mcstealth said:

"What in the Wide wide World of Sports"  is blobby?

 

Name that Movie

Keyboards error.  I joined Mooneyspace to communicate with other owners.  

I guess I'll just not comment on Mooneyspace anymore.