Is this Piston burned? Borescope images

[Grandmas Flying Couch]

Hello All!,

It's a year since I had a cylinder changed after losing 4 quarts in 1 hour of flight!  My oil consumption is still pretty high about 1 quart every 4 hours.  Here are some pictures of the cylinders pistons and exhaust valves along with the spark plugs.  The exhaust valve is the last pic per cylinder and are in order from 1 to 4.  The spark plugs are labeled.  What do you guys think?  The scratch is just the borescope pushing carbon off the valve on the way in. 

Cylinder 4 the last piston pic has a different colored part of the piston on top, is that a hot spot?  Cylinder 4 only has about 60 hrs since being redone and the others have 475hrs.  

The fourth pic has a build up of what I suppose is lead, I have put a about 150 hours on the engine,  I was guilty of running full rich alot when I was getting my license.  I now cruise at 6-12k 25deg LOP or 100 deg ROP  I wonder if this build up will reduce or reverse a little.  

The first exhaust valve pic is not symmetrical but I don't think it's heat damage, I think it's residue from oil or fuel.  

All cylinders have visible crosshatch with almost no scoring in the direction of piston travel.  Cylinder 4 has a drastically different color, I wonder if it is running differently or if it just because it has less time.  I have also been running much leaner since getting it back on.  I do not lean much below 5k.

I plan on removing the injectors and running a flow measurement with 4 identical containers and measuring the output at full rich and with the mixture half way out and see if I'm getting a drastically different fuel flow.  

Any observations would be greatly appreciated!

  

[Grandmas Flying Couch]

Here are some pics of tailpipe I forgot..... 

[EricJ]

I'm not seeing anything alarming there, but I'm not as experienced as some.

 

[PT20J]

I'm not the most versed on this either, but I don't see anything that looks like a burned piston (pictures I've seen show a lot of discoloration, and melting on the outer edge which is generally the result of detonation or preignition), The valves look fine. You can search the web and find pictures of distressed valves. The only thing that stands out is quite a bit of lead deposits on the bottom spark plugs.

[Ragsf15e]

Your engine management sounds fine in the air, what about on the ground?  You can keep the lead fouling at a minimum by leaning aggressively right after start and again right after landing.  You can go a bit richer for the runup as desired.

When i say aggressively, I mean you shouldn’t be able to add power to taxi without adding a little rich mixture.  You should be that lean anytime you’re on the ground.  I’ve never noticed a problem with temps and you’re at such low power, it won’t hurt the engine.

[Gary0747]

High oil consumption might be a break in issue with not getting the rings set?

[Hank]

1 hour ago, Ragsf15e said:

Your engine management sounds fine in the air, what about on the ground?  You can keep the lead fouling at a minimum by leaning aggressively right after start and again right after landing.  You can go a bit richer for the runup as desired.

When i say aggressively, I mean you shouldn’t be able to add power to taxi without adding a little rich mixture.  You should be that lean anytime you’re on the ground.  I’ve never noticed a problem with temps and you’re at such low power, it won’t hurt the engine.

This is what I do in my C, the Mixture lever ia about 3/4 towards lean. One time when parked on the grass, I cranked, leaned, taxied to the edge of the pavement, pushed a little throttle to climb up and the engine almost died--a surprise at first, I locked brakes, scanned things, remembered the mixture, pushed some richer and it smoothed out. Then added throttle, pulled onto the pavement and retarded both throttle and mixture for taxi.

7 hours ago, Grandmas Flying Couch said:

I was guilty of running full rich alot when I was getting my license.  I now cruise at 6-12k 25deg LOP or 100 deg ROP  I wonder if this build up will reduce or reverse a little. . . .  I have also been running much leaner since getting it back on.  I do not lean much below 5k.

. . . Any observations would be greatly appreciated!  

Question:  why do you run Full Rich below 5000 msl? That was standard practice in the flight school Cessnas, but my C has Performamce Charts for Sea Level, 2500, 5000, etc, up to 12,500. I use the low level ones just like I do the hjgher altitude ones. It'll be different for your F, but I make flightseeing and lunch runs often at 2500 / 3000 msl and run 23" / 2300, leaned to 50° ROP, and generally indicate ~145-150 mph there. (Carbed engines are difficult to run smoothly LOP.    But I can't complain about 147 KTAS on 9-ish gph block time at altitude.)

I rarely have any lead on my (massive) plugs, and when I do, it's fairly large balls down inside, nothing that would show up in these photos. While far from a bore scope expert, I think these pictures are fine, but the plugs look like something is unhappy. The gray exhaust is good, though. 

[N201MKTurbo]

Did you scratch that valve with the bore scope?

[jlunseth]

Oil "consumption" doesn't just occur in the cylinders, in fact with that kind of oil usage, 1 quart every 4 hours, and no obvious signs of it in the cylinders I would be looking elsewhere - for a leak.

[Cruiser]

all your bottom plugs look oil soaked. 

One qt/4 hours is high but not serious. A little effort can isolate the excessive leakage with compression testing. Valves vs rings and which cylinders are better/worse than others. 

LOP is not going to show much change in only 100 hrs or so. It is a long term benefit. 

The appearance of your tail pipe is pretty normal for LOP operations. Talk with your mechanic about the lead fouling, sometimes a slightly hotter plug or a change to the cruise settings will help reduce it. It will never be completely eliminated. 

[Grandmas Flying Couch]

On 10/24/2020 at 3:47 PM, PT20J said:

I'm not the most versed on this either, but I don't see anything that looks like a burned piston (pictures I've seen show a lot of discoloration, and melting on the outer edge which is generally the result of detonation or preignition), The valves look fine. You can search the web and find pictures of distressed valves. The only thing that stands out is quite a bit of lead deposits on the bottom spark plugs.

I'm starting to think cylinder 4 might be the only one not burning oil so perhaps its the healthiest. 

On 10/24/2020 at 4:12 PM, Ragsf15e said:

Your engine management sounds fine in the air, what about on the ground?  You can keep the lead fouling at a minimum by leaning aggressively right after start and again right after landing.  You can go a bit richer for the runup as desired.

When i say aggressively, I mean you shouldn’t be able to add power to taxi without adding a little rich mixture.  You should be that lean anytime you’re on the ground.  I’ve never noticed a problem with temps and you’re at such low power, it won’t hurt the engine.

That's exactly how I lean on the ground and my engine used to after fire in the exhaust from time to time.  After a two years of leaning till the rpm drops a little from 1300 to 1200 the engine has all but stopped the after firing.   I suspect exhaust valves were starting to stick.  

 

On 10/24/2020 at 5:05 PM, Gary0747 said:

High oil consumption might be a break in issue with not getting the rings set?

I fear this might be the case, if it is, I'm not sure there is much I can do besides major surgery.  I'm going to go after all other avenues first.  Cylinder 4 died a year ago due to "gummed up rings"  both compression and oil control rings.  

 

On 10/24/2020 at 5:50 PM, Hank said:

This is what I do in my C, the Mixture lever ia about 3/4 towards lean. One time when parked on the grass, I cranked, leaned, taxied to the edge of the pavement, pushed a little throttle to climb up and the engine almost died--a surprise at first, I locked brakes, scanned things, remembered the mixture, pushed some richer and it smoothed out. Then added throttle, pulled onto the pavement and retarded both throttle and mixture for taxi.

Question:  why do you run Full Rich below 5000 msl? That was standard practice in the flight school Cessnas, but my C has Performamce Charts for Sea Level, 2500, 5000, etc, up to 12,500. I use the low level ones just like I do the hjgher altitude ones. It'll be different for your F, but I make flightseeing and lunch runs often at 2500 / 3000 msl and run 23" / 2300, leaned to 50° ROP, and generally indicate ~145-150 mph there. (Carbed engines are difficult to run smoothly LOP.    But I can't complain about 147 KTAS on 9-ish gph block time at altitude.)

I rarely have any lead on my (massive) plugs, and when I do, it's fairly large balls down inside, nothing that would show up in these photos. While far from a bore scope expert, I think these pictures are fine, but the plugs look like something is unhappy. The gray exhaust is good, though. 

I don't really cruise below 5000' anyway and it's often over 100F outside so I tend to climb till the vents spit 75F air.  CHT can get rowdy if I lean too aggressively on the climb.

 

On 10/24/2020 at 6:41 PM, N201MKTurbo said:

Did you scratch that valve with the bore scope?

Yes, yes I did, I'm going to be more careful.  

On 10/24/2020 at 8:49 PM, jlunseth said:

Oil "consumption" doesn't just occur in the cylinders, in fact with that kind of oil usage, 1 quart every 4 hours, and no obvious signs of it in the cylinders I would be looking elsewhere - for a leak.

No leaks, looked for that.  Followed Saavy aviations youtube video, oil can only get out from leaks, burn it, or spit it out the breather.  No leaks, exhaust is not really oily, but the belly is oily.  I suspect blow by.  

23 hours ago, Cruiser said:

all your bottom plugs look oil soaked. 

One qt/4 hours is high but not serious. A little effort can isolate the excessive leakage with compression testing. Valves vs rings and which cylinders are better/worse than others. 

LOP is not going to show much change in only 100 hrs or so. It is a long term benefit. 

The appearance of your tail pipe is pretty normal for LOP operations. Talk with your mechanic about the lead fouling, sometimes a slightly hotter plug or a change to the cruise settings will help reduce it. It will never be completely eliminated. 

There was a little oil in each cylinder when I borescoped it.  There wasn't any wet oil on the plugs.  The threads have oil because I put oil on the threads when I installed them.  The engine is either burning oil or blow-by is pressuring the case and causing it to spit up.  

Aggressive leaning on the ground and in cruise has eliminated the after fires in the exhaust I used to get.  I believe the exhaust valves were beginning to stick at low power.  

Thank you for all your Help!

[EricJ]

1 minute ago, Grandmas Flying Couch said:

Yes, yes I did, I'm going to be more careful.  

The "scratch" isn't a big deal as long as it's known that it was the borescope, which it seems like it usually is.   It can be hard to avoid if you're poking around there in the dark.

 

[Grandmas Flying Couch]

On my path to reduce oil consumption I have started taking measures I created the whistle slot according to the AD posted here on mooneyspace and I moved the crank case vent hose up a little where it comes off the accessory case so It has a little more up hill before it comes down to vent.  

I'm doing all the cheap stuff first.  

 

[EricJ]

I need to do that.   I cut the vent in the hose and it occasionally makes a mess inside the cowling.   I think your way is better.

[Grandmas Flying Couch]

Because of the way the aluminum tube is positioned in the air stream I think it is creating a slight suction which my be helping to suck out the oil mist in the engine.  This was also featured in the SAAVY youtube film about oil consumption.  The whistle slot will relieve some of this vacuum.  

[Grandmas Flying Couch]

Just now, EricJ said:

I need to do that.   I cut the vent in the hose and it occasionally makes a mess inside the cowling.   I think your way is better.

I read that about yours and then found this ad, your push on the screw driver while sliding side to side, shapes the bottom out and the top in which I think will hopefully stop any mess.  

[Grandmas Flying Couch]

Here is the AD I forgot to post it.  

[jlunseth]

1 hour ago, Grandmas Flying Couch said:

No leaks, looked for that.  Followed Saavy aviations youtube video, oil can only get out from leaks, burn it, or spit it out the breather.  No leaks, exhaust is not really oily, but the belly is oily.  I suspect blow by.  

I don’t disagree with the formula - leak, burn it, or spit it out the breather. I used to think 1 qt. in 4 hours was just something aircraft engines would do, or that it necessarily indicated it was being burned out or spit out. Then one night having crossed Lake Michigan and being at 19 k there was no more oil and an emergency landing in Can. was necessary. A small long sliver of plastic had entered the quick drain and lodged in the seal, so when a mechanic shut the drain it would not fully close. Run the engine, compress the air in the sump, and it only takes about 2 hours to blow out the oil all over the belly. If the leak is big enough. IRANd the engine, changed the quick drain, chased down the leaks and normal is now 1 qt. per oil change and that’s more than 800 hours later. 

Your plane and hopefully you will find the problem, but in my aircraft (231) even with tired old rings, a quart every 4 hours is a leak, not burn it or spit it out.

[carusoam]

When looking at exhaust valves...

We are looking for two things...

1) Nice concentric circular patterns that look similar to a pizza and its crust...
 

2) No strange edge effects that disturb the concentric pattern...

Did. You have an engine monitor to share some EGt details?

This pic, is missing the pizza.... 

It looks like it has some big edge effects, typical of a valve that is struggling to rotate...

Compare to the other three...

Probably not the source of an oil leak... but exhaust valves are cooled and lubricated with engine oil...
 

Sometimes oil leaks by the oil rings... age, wear, or broken...
 

If the bottom plugs are wet... oil is getting in the cylinder...

Taking pics of the cylinder walls may reveal something missing, worn away, or cracked...

There should be a cross-hatched pattern that was put there with a hone... if it is worn away, or a coating has failed, or there are giant rust pock marks... getting the cylinder surfaces honed again may be an option to consider...

PP thoughts only, not a mechanic...

Best regards,

-a-

[larrynimmo]

Could you please post the AD in it entirety....

 

thank you