Consideration of Top Overhaul

[Alan Maurer]

Mooney People, 

Ovation has just over one thousand TTSN and adding a quart of oil around every three hours. Last annual compression were in the fifties and boroscope did not see any valve issues.

I am guessing that the rings let the oil get burned but not sure if that deserves a top. A six pack from Continental , if it can be had, is around 20K. 

Engine runs well and smoothly. Would be glad for some opinions. #6 cylinder was changed at last annual for very low compression and it is fine. It was not a new one 

as they are hard to get. It came from Zephyr Hills in Florida.

Thanks

Alan

[N201MKTurbo]

You could pull the cylinders, replace the pistons and rings and re-hone the cylinders for a fraction of that amount.

You could get the valves done too, (essentually an overhaul at that point) for about half of the amount above.

[N201MKTurbo]

It is possible all your oil consumption is coming from one cylinder. How do your plugs look?

[KSMooniac]

I concur with Rich.  With ~1000 hours since new, there is a good chance your valves will need attention as Continental has been doing a poor job of valve installation for a long time, and they typically need help around 800-1000 hours.  It is highly UNlikely that your cylinders are worn out, and since you cannot get new ones easily, you ought to strongly consider getting a good shop to overhaul your current cylinders.  It should not take a ton of time if they order the parts ahead of time and schedule the work for you.  Getting the valves reworked, honing the cylinders, and using new rings and pistons will likely let you run to TBO and beyond easily.

My J came with a 1991 factory overhaul IO-360, and I did an IRAN at 1650 SMOH due to oil consumption and ran it to ~2150 SMOH when my cam failed.  I overhauled those cylinders with the engine and don't regret either of those decisions.  I may or may not overhaul them a 2nd time in the future depending on how they measure the next time.

[Utah20Gflyer]

Personally I wouldn’t try to figure out which cylinder(maybe two) is the weakest link and try a repair and see how that affects the overall situation.  A lot of the oil consumption issue could be cause by one or two of the cylinders.  A top overhaul might be euthanizing a bunch of cylinders that still have life in them.  
 

I don’t think compression in the 50s is necessarily a big issue by itself but a quart in 3 hours is fairly high oil usage.  I’d consider it time to start doing something. 
 

If you just want to be done with it and can actually get the cylinders you could just write a big check.   I would do the incremental approach.  But that’s just my preference.  
 

[dkkim73]

Is there air leakage past rings on any cylinders? I had good luck with the Savvy ring flush procedure. 

As for compressions being marginal, could be valves or rings. Potentially there are inexpensive mitigations if no major damage has occurred. 

Some shops are very comfortable lapping valves in place and trying the ring flush, and some look at you like you grew a second head. 

 

[anthonydesmet]

Agree with all above. Is your oil analysis’ running flat and your not making metal correct?

[exM20K]

Continental Service Bulletin M89-9 is an easy and effective way to see if a jug or jugs have lost their dynamic seal.

It’s not always easy, but a good borescope imagery set will show the condition of the cylinder walls (corrosion and/or loss of crosshatch).

I have no experience with the Savvy ring wash, but if it’s the cylinder walls, you’re probably going to need new jugs or work on what you have.  I got away with punching the old cylinders 0.01 over, but that is a one-time only thing. I got 1000 hours out of that work.

I recently went through the same stuff again and elected to replace all six with a balanced set from Continental, and the result has been a very smooth engine. I would strongly recommend getting the moving stuff mass balanced either from continental or from one of the good cylinder shops.

-dan

[A64Pilot]

16 hours ago, N201MKTurbo said:

You could pull the cylinders, replace the pistons and rings and re-hone the cylinders for a fraction of that amount.

You could get the valves done too, (essentually an overhaul at that point) for about half of the amount above.

This is the way I’d go. Often if they are well worn they can hone to an oversize with new pistons and if you get the valves done, many replace exh valves, it’s in effect an overhaul. By valves being done I mean new valve guides too. Apparently factory Continental cylinders have very poorly done valve guides, many better shops disassemble new factory Conti cylinders and rework the guides and those last longer.

As far as balancing, sure why not, but all you can balance is the pistons of course. You get the most from balancing the crank and rods but of course you can’t do that now.

Often by addressing just the weakest cylinder your in the shop every other month replacing the next one when it goes, you end up with an airplane that lives in the shop because they don’t have spares on the shelf and it ends up costing way more doing one at a time. Plus you may not be at home when one demands attention.

Other side of that argument is it does spread the costs out if you simply can’t afford to get them all done at once.

Edited March 29 by A64Pilot

[MikeOH]

22 hours ago, N201MKTurbo said:

You could pull the cylinders, replace the pistons and rings and re-hone the cylinders for a fraction of that amount.

You could get the valves done too, (essentually an overhaul at that point) for about half of the amount above.

Curious why the need to replace the pistons (assumes no actual damage to them is found)?  Wouldn't the hone and new rings address the issue?

[Schllc]

I’m pretty sure cylinders are in stock and shipping immediately from AirPower.
that being said, if it’s making full power, and running smooth I would keep flying.  
compression tests are just not that critical. 
are you sure it’s burning and not blowing out?

all of my airplanes have had a sweet spot between 5-7 qts indicated and anything over that just blows out. 

[N201MKTurbo]

1 hour ago, MikeOH said:

Curious why the need to replace the pistons (assumes no actual damage to them is found)?  Wouldn't the hone and new rings address the issue?

I have found the pistons wear more than the rings do. Most people just think about the rings sealing on the cylinders, but they seal on the piston as well. The top and bottom of the rings have to form a seal in the groves in the piston. I have found the groves get a taper to them after a while. 
 

If you are going to reuse the piston you should clean according to the service manual. It is very tedious. They don’t allow any kind of abrasive blasting. I have found tooth brushes, string and comet cleanser works fastest. Expect at least 1/2 hour per piston, if you are good.

[dkkim73]

There was a comment above about getting 1000 hrs out of a cylinder. What do you guys find a reasonable service life? I replaced two originals recently in the mid 1500's (after lapping and ring flush about 40-50 hrs ago) and one of the 1000-hr cylinders just a few weeks ago. 

[exM20K]

10 hours ago, A64Pilot said:

As far as balancing, sure why not, but all you can balance is the pistons of course. You get the most from balancing the crank and rods but of course you can’t do that now.

True.  In my case, the engine began life as a Continental Platinum Edition, which had all the rotating bits balanced, so maybe that is why the result with a matched set of pistons is so good.

-dan

[A64Pilot]

16 hours ago, dkkim73 said:

There was a comment above about getting 1000 hrs out of a cylinder. What do you guys find a reasonable service life? I replaced two originals recently in the mid 1500's (after lapping and ring flush about 40-50 hrs ago) and one of the 1000-hr cylinders just a few weeks ago. 

From my experience it depends on how hard they are run, 1000 hours is good if you bought a Mooney to go fast and don’t mind paying for the speed, some won’t get that.

But average use I think is about 100 hours a yr, 1,000 hours is 10 years. So there’s that.

I’ve seen Conti cylinders if run at 65% power or less go to full TBO

[A64Pilot]

15 hours ago, exM20K said:

True.  In my case, the engine began life as a Continental Platinum Edition, which had all the rotating bits balanced, so maybe that is why the result with a matched set of pistons is so good.

-dan

My Lyc all rotating components are balanced to 1 gram or less, it’s the only smooth 4 cyl I’ve ever flown behind, I believe being smooth means it and everything else will last longer, of course the prop needs to be balanced too.

[TangoTango]

@A64Pilot I assume this was done as part of a field overhaul? Do you know who did the work? I'm not aware of lycoming ever offering that as a factory option

[A64Pilot]

@TangoTango I was afraid someone would ask that, I’ll come up with his name eventually. He’s in North Ga and I believe was a Nascar engine builder, he does do overhauls to very exacting specs, he does offer a performance engine where he has the heads ported and polished, a 7 angle valve job and the guides are honed not reamed to size. Pretty sure he CC’s the heads etc like you do in a well build car hot rod motor. I think he balances all his engines to less than 1 gram, but maybe that’s just the performance overhauls, not sure. You know his engines right off because lots of bits are powder coated red, but I’ve heard he will do other colors, or I’m sure leave them stock.

Finally came to me, his Name is Carlus Gann, if your interested call about a performance engine.

https://www.gannaviation.com/engine-overhauls

 

Edited March 30 by A64Pilot

[M20F]

IRAN, the only thing I would say never skimp on is  if you do the bottom do it all (the bottom that is).  Otherwise IRAN. 

[exM20K]

1 hour ago, A64Pilot said:

My Lyc all rotating components are balanced to 1 gram or less, it’s the only smooth 4 cyl I’ve ever flown behind, I believe being smooth means it and everything else will last longer, of course the prop needs to be balanced too.

One would hope.  Smooth definitely makes *me* last longer.  Noise/vibration are very fatiguing on longer flights.

-dan

[A64Pilot]

52 minutes ago, exM20K said:

One would hope.  Smooth definitely makes *me* last longer.  Noise/vibration are very fatiguing on longer flights.

-dan

Remember I was a helicopter mechanic for 4 years and a helicopter maintenance officer for 15. 

EVERYTHING on a helicopter vibrates, the trick is to minimize it as much as possible if you do everything lasts longer even the electronics

[Fly Boomer]

20 hours ago, dkkim73 said:

There was a comment above about getting 1000 hrs out of a cylinder. What do you guys find a reasonable service life?

I think it depends on multiple factors:

1. who built the engine
2. what parts did the builder use
3. how hard you run them
4. luck
5. probably many others

Here is an article from a guy who gets remarkable life from his engines:

https://www.savvyaviation.com/the-great-beyond-tbo/

 

 

[Schllc]

20 hours ago, Fly Boomer said:

I think it depends on multiple factors:

1. who built the engine
2. what parts did the builder use
3. how hard you run them
4. luck
5. probably many others

Here is an article from a guy who gets remarkable life from his engines:

https://www.savvyaviation.com/the-great-beyond-tbo/

 

 

completely agree with this assessment, the challenge is when you buy an engine with 1600 hours and come to the point of tbo and you do not know how it was treated those 1600 prior to you.  Not saying this changes the guidance, but it certainly is a factor few of us can ignore.

The best thing that can be done to fly an engine past tbo is to actually fly regularly....

[mooneyflyfast]

A quart in three hours is well within limits (look up Continental’s acceptable limits). As long as you have acceptable compression and it runs good don’t mess with it.  Anytime you remove all the cylinders you are opening up the risk of all kinds of catastrophic engine problems. . Check what Mike Busch has to say about this. I think he  recommends to avoid top overhauls if possible.  I might try some of the possible non disassembly measures like ring flush or even MMO in the oil and gas. (don't laugh I was a skeptic but it saved me having to remove a cylinder to fix a persistent valve sticking problem) I wouldn’t have tried it except that it was recommender by an old timer cylinder shop owner. lif you are using multi vis oil, try straight 50 weight.

[TheBearFlies]

On 3/28/2025 at 3:38 PM, Alan Maurer said:

Mooney People, 

Ovation has just over one thousand TTSN and adding a quart of oil around every three hours. Last annual compression were in the fifties and boroscope did not see any valve issues.

I am guessing that the rings let the oil get burned but not sure if that deserves a top. A six pack from Continental , if it can be had, is around 20K. 

Engine runs well and smoothly. Would be glad for some opinions. #6 cylinder was changed at last annual for very low compression and it is fine. It was not a new one 

as they are hard to get. It came from Zephyr Hills in Florida.

Thanks

Alan

Lower compression on the IO-550-G are acceptable. If the bore scope did not reveal valve damage, I would hesitate without further evidence. Mine will reject any oil level over 7qts out the breather and down the belly. Happy spot 5-7qts. If bore scope is good, analyze engine data? That engine is running de-rated on way less power than it was built for and should run well beyond TBO if operated  properly. Look for other evidence before you invest in pulling jugs.