Low compression on #5 in IO550G Ovation; pull cylinder?

[THill182]

I know this must have been discussed before, but I cannot find it using the search facilities:

 

My M20R (2000, 310hp upgrade) has about 1000 hours on the engine (actually the top; the bottom was overhauled separately about 500 hours ago; long story...). I started noticing increased oil use, and we did a hot compression check. All came out at >70 except #5 (the "hot one"), which clocked in at 62. Further, the spark plugs showed some signs of burned oil. The other spark plugs where clean.

 

I am doing an oil analysis this week. If that comes back clean (the last one 3 months ago had very little metal, below average), would you recommend I pull the cylinder and replace it? If so, how much should that cost, approximately? Note that the engine is running great otherwise, and as I said, the bottom part is overhauled and has less than 600 hours. My plan was to fly for another 800 hours or so, and then put a new engine in it.

 

What also worries me a bit is that the oil usage came up suddenly. After the last oil change, I used about 1QRT for every 10 to 15 hours. Now it is more like a Qrt for 4 to 5 hours or less.

 

Does anyone else have experience with these types of symptoms?

 

As always, words of wisdom and from the "been-there-done-that" fellow pilots are greatly appreciated!

[DonMuncy]

If it were only the low compression, Continental says to fly it for half an hour or so and check it again. In most cases the compression will show different then. However the fouled plug and the oil consumption are a different story. I would find someone who has, and knows how to use a borescope and take a look. Go from there. 

[carusoam]

Haven't seen anything posted regarding this issue...

has the plane taken any time off recently?

sounds like a stuck ring.  Followed by exhaust escaping into the oil pan and blowing oil out the vent.

look on the hangar floor for a drip of oil that came off the gear door.

does the oil look dirtier than usual?  it may have an exhaust smell to it as well...?

#5 is the front cylinder behind the alternator.  It may run a few degrees hotter than the other cylinders.  The hangar fairy's Union has given some guidelines on a vent hole in this area.

Best regards,

-a-

[kmyfm20s]

62 not bad, run the engine again and do another test. How much hotter is it? 5 runs hot because of the alternator in front of it. Do a search for Pixie holes. It's a method to get 5 in line with the others. How do you run your engine, ROP or LOP? I would also do an in flight mag check and download the engine data and if you want post it. All of use lawn chair mechanics can give you plenty of cheap irrelevant advice:) I'm not a Mx BTW.

[THill182]

Thanks for replies!

I have been flying regularly, with occasional breaks for up to 3 weeks. I am using Camguard to hopefully prevent rust.

There is no oil on the floor, or any signs of oil leaking. I have had small oil leaks, and usually, they leave tiny droplets of oil on the windshield after flights, as the oil works its way out of the engine -- anyway that is what it looked like before. The engine compartment is dry.

I have the #5 vent hole, and it did fix the temperature problem. After the overhaul and for the last 900 hours, I rarely see CHT's above 380F, and only on very hot summer days climbing out. In cruise everything settles at LOP with CHT's below 340F, and on cooler days 320F. (Although, for about a year after the 310 conversion, a shop set up my fuel flow too low, and consistent with the 280HP version, resulting in relatively hot climb-outs).

The engine runs great, and I have detected nothing unusual for the past 20 hours of X-country flying. #5 does not run any hotter than the other cylinders, and performance and LOP power settings are identical and as good as it has always been. The ONLY thing different is that starting last month on 3 flights, I had to put in a quart of oil (3-5 hour flights). Also, I "feel" as if  as if this started only after the first 12 hours or so on the new oil. So perhaps this has to do with the older oil (but never noticed that before).

Anyway, I will analyze the oil, change the oil, and then fly it for 10 hours and watch if the oil consumption stabilizes or returns to normal. The mechanic at my airport specializes on engine overhauls so I believe has all the equipment including borescope to look into the cylinder; i'll ask him to do that next also...

[kmyfm20s]

I'm with Carusoam on this, stuck or broken ring. Burning oil from what I understand will cause slightly higher EGT's and lower CHT because of the delayed combustion event. If you do have data to anylize you might look for that. Ring bypass should be audible with a compression test. I don't know if a bad valve stem could allow that much oil to pass but might be worth looking at. A good bore scope would be beneficial.

[Jeff_S]

I also think it seems like a stuck ring is a strong possibility. But after you have it checked, if it does turn out to be a cylinder issue, I don't think you need to jump to a replacement conclusion. Many cylinder issues can be fixed quite easily and quickly with an IRAN (inspect and repair as necessary) so don't let your A/P talk you into a complete replacement "just because".

[Cruiser]

When was the #5 cooling hole installed? How many hours on that cylinder BEFORE the change? 

The alternator causes a cooling problem with that cylinder and it will easily run into the mid 400s because of it. If this cylinder has a couple hundred hours on it at those elevated CHT it probably has a stuck ring and burned/coked up oil in the ring grooves. 

It will never get any better. Put up with it (probably not a serious problem) just increased oil consumption or replace it. 

[THill182]

2 hours ago, Cruiser said:

When was the #5 cooling hole installed? How many hours on that cylinder BEFORE the change? 

The alternator causes a cooling problem with that cylinder and it will easily run into the mid 400s because of it. If this cylinder has a couple hundred hours on it at those elevated CHT it probably has a stuck ring and burned/coked up oil in the ring grooves.

I put that hole in a long time ago, and before the top overhaul which now has 1000 hours on it. It did solve my high CHT problem on #5 quite nicely.

I should have a report back on the borescope inspection and oil analysis very soon. I hope you'all are right that it is a stuck ring. What surprised me was how suddenly this came about. For the last oil change at 30 hours, I used 1 qrt. For the fist 10 hours after the current oil change I didn't put any oil in it, and then suddenly no matter how much oil I put in I am stuck below 6qrt on the dipstick (even after sitting in the same hanger, and for a few days to let the oil settle; also I have an air-oil separator, so usually, when I am filled up at 8Qrts I stay there for a long time).

[jbs007]

I have the IO-360 in an M20E but had a similar problem starting about 60 hrs into me owning it (one cylinder with low compression/fouled plugs, increased oil burn). Pulled the cylinder and there was a enough gunk in the ring groove that the rings got stuck in it and weren't expanding properly.  The piston and cylinder both looked real nice and all that was needed was to clean them out and re-ring.  Pulling a cylinder doesn't take much time and catching it early means you won't have to buy a new one which is the real expense.  Hope it's an easy fix for you!

[jetdriven]

A re-ring and home is a relatively easy job to fix a cylinder that is pumping oil.  Also, 52 PSI is acceptable compression on a continental.  You should use the master orifice tool and it can be as low at 40 IIRC. 

[MB65E]

I would not touch a thing for a while. 5 runs warm because it's usually behind a big alternator. You sound like your keeping track of things and gathering data. Keep doing that, and checking its compression on oil changes. You could also increase the frequency of oil changes. 50 to 25h. 30h to 20h etc... Whatever you prefer. That #5 cylinder is can be problematic, it's the hottest on race engines as well. Keep it cool with fuel and monitor until your not comfortable with it any longer. You'd be shocked with how low the master orifice allows on the test... 42psi I believe .

62 is great for a large continental. I'm suprised the others are that good. 

Have fun-keep tracking.

-Matt

[philiplane]

These engines make full power even down to 30 psi static compression. They will just use more oil. Depending on the master orifice reading of the day, if you follow the Continental service bulletin, the compression may be in the upper 30's and still be airworthy. It's relatively normal for 550's to drop into the 50-60 psi range after 800 hours, and basically stay there until the engine is ready for overhaul. It's also rare for a 550 to maintain compression in the 70's past 800 hours. It's nothing to worry about unless you want to spend some money for the sake of a higher compression reading.

[kmyfm20s]

The last time I took my compression I had 1 cylinder show a 52. I did another short ground run and it went back to 73 just like that. Was the spark plug wet with oil or just looked like it was burning oil? That plug might just not be firing and why an in flight mag check would be helpful. 

[THill182]

Thanks for all the feedback!

Regarding the spark plug, it wasn't "wet" per se, just dark with carbon deposits, so looked like it burned oil (the other spark plugs where gray).

We did the borescope without anything remarkable turning up; oil change (oil filter) also normal; mailed in the oil sample. If that is normal then I just keep flying it and check the oil more regularly. As I said, all indications on the EGT/CHT, oil pressure, and performance have been normal. The mechanic on my field specializes on engine work and rebuilds, so this is in his "wheelhouse" ; he agrees that repair is always preferable and something likely indicated here if the oil usage doesn't stabilize or return to normal.

 

When I first got the plane over 12 years ago, it was used with about 800 hours. At that point the engine was in bad shape, burned oil at a qrt every 5 hours or so, and CHT's would not stay below 400 in climbout no matter what I did. Eventually, all cyclinder heads cracked likely because I transitioned in from a C182RG with a bullet proof carbureted Lycoming -- so flew the plane by the book which always gave me very high CHT's. Anyway, after the top-overhaul about 1000 hours ago the cylinders have not given me  any problems. Hope they won't start now.

 

[THill182]

PS: One other quick question:

When I change oil, usually, after putting in 8Qrts and flying it for an hour or so, the dip stick settles at 7qrts or less. So we have been putting in closer to 9qrts to start.

Does anyone know if overfilling (to 9 qrts at oil changes) can do any harm the engine? (Note that I have an air/oil separator installed).

Just curious about what can/not do harm to the IO550....

[carusoam]

There would be a Too high point when the Pistons come in contact with liquid oil at the bottom of their stroke.

Over filling would not be helpful.

from experience, I filled the oil level to the top after a flight.  Of course, a day or so later, the extra quart showed up on the dip stick...

Best regards,

-a-

[jetdriven]

7 hours ago, THill182 said:

PS: One other quick question:

When I change oil, usually, after putting in 8Qrts and flying it for an hour or so, the dip stick settles at 7qrts or less. So we have been putting in closer to 9qrts to start.

Does anyone know if overfilling (to 9 qrts at oil changes) can do any harm the engine? (Note that I have an air/oil separator installed).

Just curious about what can/not do harm to the IO550....

The dipstick shows sump oil, when you change it the filter holds nearly a quart.  But if the engine has ran in he past 48hr there is also a quart still clinging to the inside of the engine.  Don't overfill it past what the dipstick indicates as full.  Oil can foam and the oil pressure can get unsteady because the oil pump cavitates. 

[Cruiser]

On ‎12‎/‎17‎/‎2015 at 8:02 PM, THill182 said:

I put that hole in a long time ago, and before the top overhaul which now has 1000 hours on it. It did solve my high CHT problem on #5 quite nicely.

I should have a report back on the borescope inspection and oil analysis very soon. I hope you'all are right that it is a stuck ring. What surprised me was how suddenly this came about. For the last oil change at 30 hours, I used 1 qrt. For the fist 10 hours after the current oil change I didn't put any oil in it, and then suddenly no matter how much oil I put in I am stuck below 6qrt on the dipstick (even after sitting in the same hanger, and for a few days to let the oil settle; also I have an air-oil separator, so usually, when I am filled up at 8Qrts I stay there for a long time).

This does not sound right. You don't say how long it takes, but dropping from 8 qts. (full) to under 6 qts. (low) does not seem normal. Something has changed to consume that oil. If it is not blown out, then that is a lot of oil to be burned. Regardless, this part of the condition needs to be resolved. If you are saying you use 2 qts. of oil on every flight that is a problem.

[THill182]

I wanted to update this thread and close the loop.

Actually, I am still unsure of what is/was going on. Long story short, as I keep flying my plane I realize that I really don't have a good fix on my oil level. Specifically, when I park the plane in my hangar and come back two days later I usually (in the winter) had about 6qrts (a little over) on the dip stick. After I leave it in the hangar for 2 weeks it then shows 8 qrts; or almost that much. In other words, it seems to me that for whatever reason it now appears as if I am burning more oil, because of different intervals at which I fly and check oil (also, I have a new shop do my oil changes; not sure that matters). Best I can tell, my oil consumption is actually reasonable (about 1qrt per 8 hours or so; I now have about 16+ hours on the oil after the last change, and added 2 Qrts; and stand at 8 qrts on the dipstick).

What is weird is that I had this plane for 10 years, so have very standard procedures. What is new is that I fly at less regular intervals (sometimes a lot, sometimes not at all for 2 weeks or more), and that I am using Camguard regularly (nobody claims it can hurt; lots of people say it works; so why not; perhaps it makes more oil stick to the cylinder walls for longer periods of time?).

Anyway, thanks for all the input and reference points. I am happy for now, and also have an annual come up at Don Maxwell's in a month or so; I will ask him to look at my Cylinder #5 once more if he sees anything unusual.

 

 

[carusoam]

Adding to the IO550 experience.

If you fly every day...  It looks like two quarts will be spread up inside the engine.  Eight quarts are in there.  6 show up on the stick.

Let it sit for a couple of weeks... The two quarts descend back to the oil pan.  Eight quarts are on the stick.

I flew two days in a row.  It started full of oil at 8 qts. Had a few drops of oil drip out of the case vent. Checked the oil level and only saw 6qts.  It looked like I may have vented a couple of quarts overboard...

Concerned in an Apollo 13 kind of way, I had my mechanic check my logic.  That's a few drops from the case vent, not two quarts...

Didn't fly for a couple of weeks.  Like magic, the oil level is back to 8qts.

I think the hangar elves could be messing with me for having a mechanic check my oil level....

The oil burn rate of the IO550 is so low it is hard to measure without paying attention to the consistency of the measurement.  An important part of the measurement is how long since the engine has been run..?

Best regards,

-a-

 

 

[Jerry 5TJ]

I'm heartened to read these posts:  After decades of Lycoming ownership I have my first Continental --the IO-550 in my Ovation -- and its oil measurements seem mysterious.

Measured cold 24 hours after a flight it may read 6 quarts.  I add one quart, fly a few hours, then two days later I measure 8 quarts. After two more days resting the dipstick shows 8.5.   

I have started recording oil levels cold, noting days since last flight.  

I've also started recording oil level hot, 15 minutes after shutdown.  

I hope in another 20-40 hours I'll have a grip on oil consumption rates.  

 

 

[Cruiser]

two things that can effect the level of oil in the engine. 

The oil cooler can drain into the sump and it will raise the level of oil vs. not draining. 

The dipstick can lock closed on the filler tube in two orientations 180° apart, the wiping action of turning the dipstick will cause the oil to wick up the dipstick. Always check the level by having the dipstick oriented the same. I set it to have the word OIL on the cap always ends toward the back of the engine when locked closed.

[bradp]

What's a master orifice tool and how does that change the compression reading normals?

[Guest]

2 hours ago, bradp said:

What's a master orifice tool and how does that change the compression reading normals?

The master office tool is connected to the cylinder adapter to then determine what the allowable lower reading over 80 psi is.  Typically in the low 40/80 range, anything above this reading is acceptable.  Even below this number is not cause for immediate removal.

Clarence