Burning Oil after new piston and rings

[FlyboyKC]

Mooney M20G 180hp.
Oil Temp 215 - 230 degrees
CHTs 303, 330, 380, 360
EGTs 1250, 1330, 1410, 1370
Powerflow exhaust
Guppy mouth closure

So last August 2023, I started to burn more oil in cylinders 2 & 4 so I decided to hone the cylinders and put new rings and pistons in (the A&P did it). I went through the break-in process and everything seemed normal. I ran the engine rich and kept the CHTs and EGTs as low as I could get them. I have about 40 hours on the new rings and pistons and oil consumption stabilized. However, now at around 60 hours I have started to burn a lot of oil (about 1.5 Qt in about 3 hours) and getting worse. Ugg! 

So I thought maybe I glazed the cylinders. So I had the A&P check it out. Before they did anything they took a compression test on 2 & 4, both were 72/80. When they pulled the bottom plugs #2 looked okay, but #4 plug was oil soaked and there was oil pooled in the cylinder.

Another complaint I had, was that it seemed my oil temperature was running hot. This used to be a cool running engine. I replaced the oil cooler with a new high efficiency, which helped some but still running hotter than I would like. Now my oil temp is around 215 to 230 degrees in level flight (more towards the 225 range at 8000ft). I thought about replacing the vernatherm...

What concerns me the most is the condition pistons after 60 hours. Notice in the pictures there are scraps on the piston walls and one looks like it got too hot. The cylinder walls look good with no scaring.  I am wondering how this could happen? and how to prevent it from happening again?

I thought I would solicit thoughts from the collective group.

 

Thanks
Neal

[Pinecone]

What power settings for the break in?

You need to keep the power fairly high to seat the rings properly

[Flyler]

I'm an automotive/machine shop guy and don't have airplane engine experience, so take this with many grains of salt.  I wonder if you checked the cylinder bores for roundness?

[PT20J]

Looks like piston scuffing which accounts for the scoring on the skirt, the overheated appearance and the high oil temp. The question is what caused the scuffing? Assuming that the engine wasn't overheated or run at high rpm when very cold, it would likely be a parts tolerance issue. Out of round cylinder or wrong size piston? 

Sky Ranch Engine Manual: "Scuffing of the piston skirt is usually a sign of insufficient lubricating oil on the cylinder wall caused by cold engine starts. If the piston skirts are scuffed, then you should anticipate and look for spalling of camshaft lobes and followers. Scuffing can also be caused by improper cylinder barrel size."

[Ragsf15e]

2 hours ago, PT20J said:

Looks like piston scuffing which accounts for the scoring on the skirt, the overheated appearance and the high oil temp. The question is what caused the scuffing? Assuming that the engine wasn't overheated or run at high rpm when very cold, it would likely be a parts tolerance issue. Out of round cylinder or wrong size piston? 

Sky Ranch Engine Manual: "Scuffing of the piston skirt is usually a sign of insufficient lubricating oil on the cylinder wall caused by cold engine starts. If the piston skirts are scuffed, then you should anticipate and look for spalling of camshaft lobes and followers. Scuffing can also be caused by improper cylinder barrel size."

I’m curious why that would also link to spalling cam lobes?

[Shadrach]

7 hours ago, Ragsf15e said:

I’m curious why that would also link to spalling cam lobes?

I am pretty sure that the piston, like the cam, relies on splash/spray lubrication from the crank and connecting rods. My guess is that if the piston isn’t getting sufficient “splash” lubrication then it’s not likely that the proximal cam lobes are either.

[skykrawler]

7 hours ago, Ragsf15e said:

I’m curious why that would also link to spalling cam lobes?

I suspect the relationship is infrequent engine use AND cold starts - a cold start meaning very low temperature when the oil does not splash well.

There is no info on how many hours are on these cylinders.  If you hone through the hardened cylinder surface (oversize) results will not be good.  Were they Lycoming pistons?  The pits on the skirts are unusual. They don't look like 40 hour pistons.  The pistons in my 1850hr 42yr old cylinders look better than that.

[FlyboyKC]

1 hour ago, skykrawler said:

I suspect the relationship is infrequent engine use AND cold starts - a cold start meaning very low temperature when the oil does not splash well.

There is no info on how many hours are on these cylinders.  If you hone through the hardened cylinder surface (oversize) results will not be good.  Were they Lycoming pistons?  The pits on the skirts are unusual. They don't look like 40 hour pistons.  The pistons in my 1850hr 42yr old cylinders look better than that.

Thanks for the reply. Thats my concern with the pistons is the wear in such a short time. The cylinders have about 1035 SMOH. These are the Superior Steal cylinders.

As far as  cold starts, in the winter months I preheat using the Tanis system (oil pan and cylinder heaters).

[hammdo]

Maybe send the cylinder for IRAN to a cylinder shop - they can scope out the cylinder, make sure everything is in good shape, do the honing/rings/new piston/pin and pin plugs if need be. They could check the bore at the same time.

Break it in with mineral oil or something like Phillips X-country 20w50 — BTW what oil did you use for break-in — just curious…

-Don

[MikeOH]

5 hours ago, skykrawler said:

There is no info on how many hours are on these cylinders.  If you hone through the hardened cylinder surface (oversize) results will not be good.  Were they Lycoming pistons?  The pits on the skirts are unusual. They don't look like 40 hour pistons.  The pistons in my 1850hr 42yr old cylinders look better than that.

Only automotive experience to guide my opinion, but I agree that that piston does NOT look like it only has 40 hours!  Looks more like they honed the cylinder and put new rings on the OLD piston.  Again, IMHO.

Not sure if it's possible, but I'd try to do an exchange OH rather than have that cylinder/piston reworked yet again and returned to me!

[PT20J]

When I was a kid, I had two identical Jacobsen 2-cycle lawnmower engines; one on a go-kart and a spare. I took them apart just for fun and mixed up the pistons (hey, I was callow youth of ten years). When I ran the go-kart, the engine seized after it heated up and when I took it apart, the piston was scored and over heated a lot like yours. The cylinder looked fine as I recall. I swapped the pistons and it ran fine. I took from this that the mating of cylinder to piston is critical.

So, I wonder if putting new pistons in a used cylinder that has only been honed is an issue. The high oil temperature is a symptom of high internal temperatures. I also understand that excessive blowby can overheat the piston skirt and cause scuffing due to thermal expansion. Have you verified that the ring gaps are correct?

[N201MKTurbo]

Maybe the cylinders were not cleaned properly after honing.

[FlyboyKC]

16 minutes ago, N201MKTurbo said:

Maybe the cylinders were not cleaned properly after honing.

That may be a possibility.

[lanejacobs84]

Had an annual last year and we were chasing high CHTs (up to 430 max in cruise) on #1 cylinder. A&P suggested an cylinder overhaul. It was overhauled and subsequently did nothing for the high CHTs. Put in a new exhaust valve guide during that overhaul and in the past year oil consumption went up (1qt in 3.5hrs). Now my '79 J has a destroyed cylinder because the valve guide failed (literally broken in half) and started throwing metal into the oil. Compression on that cylinder was 20/80 and the valve had gas erosion. So if you had the valve guide replaced maybe check that? Something in there is making metal.

[Jblanton]

The mating surface on the case looks weird.  There is what looks like some paint transfer.  There should never be any paint on the mating parts. Was there an O-ring on the bottom of the cylinder? I doesn't look like there was one looking at the case.  Did you take the piston pin plugs out already? I don't see them.  How do they look?

[Shadrach]

1 hour ago, Jblanton said:

The mating surface on the case looks weird.  There is what looks like some paint transfer.  There should never be any paint on the mating parts. Was there an O-ring on the bottom of the cylinder? I doesn't look like there was one looking at the case.  Did you take the piston pin plugs out already? I don't see them.  How do they look?

Good catch.  I too have always thought that any sealant/gasket maker on the cylinder flange was a no no. I don’t see how the bolts achieve the proper torque (stretch) with that crap on the flange. 

[EricJ]

14 hours ago, Shadrach said:

Good catch.  I too have always thought that any sealant/gasket maker on the cylinder flange was a no no. I don’t see how the bolts achieve the proper torque (stretch) with that crap on the flange. 

It is a no-no.   The problem is that you can get proper torque initially, but if the material between the case and flange disintegrates over time and/or migrates out from between the case and flange then the cylinder is left with play and the fasteners lose torque.    This is the mechanism blamed for many catastrophic engine failures where the cylinder fasteners fail and the cylinder separates from the engine.   The mating surface needs to be clean to prevent this.