Replace 2 Cylinders or Hold Out for Engine Overhaul

[TheAv8r]

I've been reading/debating on this... my Mooney has a higher time engine (about 1600hrs SFOH) with original cylinders. When we did the prebuy, we found 2 cylinders with signs of high oil bypass, 1 cylinder's compression was pretty weak, the other's was just shy of 70. We borescoped both which revealed wet valves and scoring/etching on the sides likely due to I think broken rings? The plane continues to produce great climb & cruise power, runs smoothly, and oil consumption is around 1qt every 7hrs (some of that is due to an oil leak I'm still chasing down). The spark plugs from both those cylinders were wet with oil, consistent with the oil bypass. My A&P friend suggested I wait until annual and then replace the 1 cylinder with low compression, consider replacing the 2nd. The other two cylinders looked fine, spark plugs looked fine, and had compressions in the high 70s. The bottom end was pretty much IRANed 1000hrs ago due to a prop strike, so I suspect it's still in pretty good shape. However, we plan to overhaul the engine in the next 3 years regardless, with how much I fly it'll be TBO or past and due an OH. 

I'm debating whether I should go ahead and put in 2 new cylinders, take a look at the bottom end when we do it, and then fly it until it needs a full OH. However, what happens to those 2 cylinders when we get to OH time? If it needs OH in let's say 1yr, are those cylinders basically just wasted money? Is the better move to just keep flying it and fully OH everything (I know Mike Busch in particular is not a fan of cylinder work)? Opinions wanted...

[ShuRugal]

That sounds like an excellent question to ask Mike Busch himself. www.savvyaviation.com

7 hours to use one quart is amazing, but scored cylinders are not. Ask Mike, he'll give a better answer than any of us.

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[jgarrison]

How low is low?  Quart in 7? I have seen fresh overhauls that are worse than that.

[Browncbr1]

how much do you think an overhaul will cost now vs a couple years?   

My thinking is that if I'm going to be grounded for a few months for an overhaul, I'd rather do it on my own terms during the time of year of minimal usage.

I recently had a similar situation, but actually, my engine was lower time and it sounds like better condition... I decided to overhaul with the two questions above bearing much influence over my decision.

 

 

[DXB]

17 minutes ago, jacenbourne said:

I've been reading/debating on this... my Mooney has a higher time engine (about 1600hrs SFOH) with original cylinders. When we did the prebuy, we found 2 cylinders with signs of high oil bypass, 1 cylinder's compression was pretty weak, the other's was just shy of 70. We borescoped both which revealed wet valves and scoring/etching on the sides likely due to I think broken rings? The plane continues to produce great climb & cruise power, runs smoothly, and oil consumption is around 1qt every 7hrs (some of that is due to an oil leak I'm still chasing down). The spark plugs from both those cylinders were wet with oil, consistent with the oil bypass. My A&P friend suggested I wait until annual and then replace the 1 cylinder with low compression, consider replacing the 2nd. The other two cylinders looked fine, spark plugs looked fine, and had compressions in the high 70s. The bottom end was pretty much IRANed 1000hrs ago due to a prop strike, so I suspect it's still in pretty good shape. However, we plan to overhaul the engine in the next 3 years regardless, with how much I fly it'll be TBO or past and due an OH. 

I'm debating whether I should go ahead and put in 2 new cylinders, take a look at the bottom end when we do it, and then fly it until it needs a full OH. However, what happens to those 2 cylinders when we get to OH time? If it needs OH in let's say 1yr, are those cylinders basically just wasted money? Is the better move to just keep flying it and fully OH everything (I know Mike Busch in particular is not a fan of cylinder work)? Opinions wanted...

If your cylinders pass compression by ANY margin, you don't have a burnt valve on borescope (not sure what a "wet" valve is), you have reasonable oil consumption (which you certainly do), and no metal in the filter, then there is no debate needed here - don't pull a cylinder and keep on flying. Period. Don't do anything! 

Also note compression testing can be very operator dependent and should be retested with the engine hot if a cylinder fails cold.  And leaking past the rings is very different than leaking past an exhaust valve (should be a loud hiss at the tailpipe).  The latter can be unacceptable even with compression >>60 and should be corroborated by seeing a burnt edge on the valve.  

When absolutely have to pull a cylinder a higher time SMOH IO360 like yours, I'd save a few bucks and get it IRAN'd, particularly if they're first run cylinders. For the O-360, the cylinders are so cheap that you might as well replace it - the cost savings from IRAN are much less.

[jaylw314]

18 minutes ago, DXB said:

When absolutely have to pull a cylinder a higher time SMOH IO360 like yours, I'd save a few bucks and get it IRAN'd, particularly if they're first run cylinders. For the O-360, the cylinders are so cheap that you might as well replace it - the cost savings from IRAN are much less.

I thought the IO-360 cylinders are about twice as expensive as other cylinders, like around $2k each?  Edit:  oh wait, now I see what your saying

For OP, realize that half the people here will tell you not to bother overhauling your motor at all unless there's an indication of a bottom end problem.  Also, 1 qt every 7 hours is not automatically bad, I have a about 1 qt every 8 hours on a 400 hour rebuilt (zero time) motor that looks and runs well.

If the cylinders are borescoped every annual, suddenly seeing scoring WOULD make me pull the cylinders since it's a new problem.  You DO get them borescoped every annual, right?  If not, then it's kind of a guess or mechanic's opinion as to whether it's new or a chronic issue.

Edited November 29, 2021 by jaylw314

[Bob E]

57 minutes ago, jacenbourne said:

However, we plan to overhaul the engine in the next 3 years regardless . . .

This is (literally) the money quote. Since you're going to overhaul within in three years, why not do it now? You'll save the cost of piecemeal fixes, which would likely end up being more expensive than the cost of financing the overhaul. A zero-time engine will last for many years and will give you peace of mind - no more constantly hauling out the borescope and wondering which cylinder to replace next.

[Shadrach]

How often did the bird fly before you purchased it?  You need to determine where the leak is in each cylinder. Reading a borescope is as much art as science. It takes an experienced eye to understand everything on the screen. If it's an exhaust valve, it should be corrected ASAP. Valves can be lapped and exhaust guides replaced without removing the cylinder.  Cylinders need not be replaced just yet but should be monitored closely.

[Utah20Gflyer]

Since you did the bottom end 1000 hours ago I would say do cylinders rather than a complete overhaul.   You could easily get another 1000-2000 hours out of the engine if nothing crazy happens and since it isn't urgent I would get an appointment setup with a specialized engine shop and have them ready with the parts and hopefully you can get a quick turn around on the work.  

Remember though, two cylinders at the same time is major engine work and needs to be done very carefully by someone who does it all the time.  You can loose tension on your main bearings if not done correctly and end up with a fubar engine or worse.  

See Mike Busch's podcast on the dangers of cylinder work for a more complete picture of what I am talking about. 

In the end though it's your money, so what you prefer is the right answer.  

[KSMooniac]

Many years ago I IRAN'd all 4 cylinders at 1650 SMOH (first run) and got another 500 hours until my cam failed. I overhauled the cylinders with the rest of the engine at that time and put them back in service. I would just IRAN your two problem cylinders and keep going. Inspect the cam when you have at least one cylinder off... If it is bad then OH everything.

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[PT20J]

On 11/29/2021 at 11:10 AM, jacenbourne said:

scoring/etching on the sides

If by the "sides" you mean the 9 o'clock and 3 o'clock positions, this might be due to piston pin scuffing.

[MBDiagMan]

As long as it is not making metal and it is holding good oil pressure, overhaul or replace cylinders as needed.  Cylinders are just no big deal compared to splitting the case.  Consider cylinders almost as accessory items.  When cylinders are removed, inspect cam and lifters CLOSELY.  If cam and lifters look good, go ahead with the cylinder replacement or overhaul.

Edited December 1, 2021 by MBDiagMan

[BKlott]

An oil leak which you have trouble finding may very well be the result of a cracked crankcase. Oil stains on the case with no apparent source of the associated leak can be a good indication of this. The next indications may be a little sluggish climb followed by a high oil temperature reading along with a low oil pressure reading. A little roughness upon power reduction, followed by an immediate return to the field led to DIVCO determining that mine was “cracked beyond repair”.

Putting two new cylinders on a 1,600+ hour engine would not be the best use of your money, in my opinion. My engine was at 1,400+ smoh and about 24 years when it decided that it was time for a major. I was able to return to my airport where Zephyr Aircraft Engines just happens to be located and had enough altitude to enter downwind at 1,800 ft, some 1700+ ft AGL. It was a low stress, nearly ideal time for my engine to make my decision for me. In retrospect, I should have the pulled the engine and had it done much sooner.

As one very experienced CFI (he helped me get my Instrument and Commercial back in the 1980s) said to me after the event, “you were very, very lucky”.

So about five months and nearly $40 AMU after the event, I got my airplane back in the air. I am now enjoying flying behind the smoothest running O-320 that I have ever flown behind in my life. I now have 11.5 hours on it following Zephyr’s major overhaul to new limits and the difference between this engine and the tired engine that I was flying behind is like night and day! 

Spending money for piecemeal repairs to your engine will not add value to your airplane. It will not make it easier to sell if you end up needing to do that. The ads that have stuff like “1,900 since major, 1200 since bottom end, 300 since two new cylinders” say one thing to any knowledgeable buyer: the engine needed to be overhauled and the guy didn’t want to spend the money to do it right. Move on to the next ad or make an offer that takes the cost of the new engine overhaul into consideration. Either way, the owner/seller is going to bear the cost of the engine job that wasn’t done.

If you were planning on the engine job in the near future anyway and your engine is giving you signals, I would bite the bullet and get the job done and get it done right. I would stop fooling around with a tired engine. You might not be as lucky as I was.
 

 

 

[MBDiagMan]

1 hour ago, BKlott said:

An oil leak which you have trouble finding may very well be the result of a cracked crankcase. Oil stains on the case with no apparent source of the associated leak can be a good indication of this. The next indications may be a little sluggish climb followed by a high oil temperature reading along with a low oil pressure reading. A little roughness upon power reduction, followed by an immediate return to the field led to DIVCO determining that mine was “cracked beyond repair”.

Putting two new cylinders on a 1,600+ hour engine would not be the best use of your money, in my opinion. My engine was at 1,400+ smoh and about 24 years when it decided that it was time for a major. I was able to return to my airport where Zephyr Aircraft Engines just happens to be located and had enough altitude to enter downwind at 1,800 ft, some 1700+ ft AGL. It was a low stress, nearly ideal time for my engine to make my decision for me. In retrospect, I should have the pulled the engine and had it done much sooner.

As one very experienced CFI (he helped me get my Instrument and Commercial back in the 1980s) said to me after the event, “you were very, very lucky”.

So about five months and nearly $40 AMU after the event, I got my airplane back in the air. I am now enjoying flying behind the smoothest running O-320 that I have ever flown behind in my life. I now have 11.5 hours on it following Zephyr’s major overhaul to new limits and the difference between this engine and the tired engine that I was flying behind is like night and day! 

Spending money for piecemeal repairs to your engine will not add value to your airplane. It will not make it easier to sell if you end up needing to do that. The ads that have stuff like “1,900 since major, 1200 since bottom end, 300 since two new cylinders” say one thing to any knowledgeable buyer: the engine needed to be overhauled and the guy didn’t want to spend the money to do it right. Move on to the next ad or make an offer that takes the cost of the new engine overhaul into consideration. Either way, the owner/seller is going to bear the cost of the engine job that wasn’t done.

If you were planning on the engine job in the near future anyway and your engine is giving you signals, I would bite the bullet and get the job done and get it done right. I would stop fooling around with a tired engine. You might not be as lucky as I was.
 

You make a good point about the oil leak, but every engine is different.  You also make a good point about buying a plane with a high time engine, but the OP is not looking to buy it or sell it.  The OP is looking for the best approach moving forward with a high time engine.  It’s quite common for these Lycomings to make it pretty far before overhauling and replacing cylinders for extended use before complete overhaul.

Relative to the cost of a complete overhaul, the price of overhauling a couple of cylinders in exchange for several hundred more hours can be money well  spent.  
 

Curing the oil leak to make sure it’s nothing serious before moving forward is a must, but if the leak is fixed, replacing a few cylinders would be a viable approach moving forward.

 

 

[TheAv8r]

Thanks for the advice all. The oil leak my A&P investigated and are pretty confident it's a worn seal in between the #3 cylinder & the case, something not really worth fixing unless we're doing cylinder work. Every indication I have is that the engine is in very good health outside of these 2 cylinders with clean oil filters, smooth running, proper takeoff & cruise power and a pretty clean engine overall, so what I will likely do is overhaul the 2 problem cylinders and reinstall them on the engine then do a full OH with new cylinders in the next few years, pending the condition of the bottom end.

[Bartman]

I had an oil leak and thought it was a bolt that went thru the case. We pulled cylinders in anticipation of reconditioning and reinstalling, but the single worn cam lobe changed all of that. The subsequent discovery of the cracked case which was the cause of the oil leak was not expected. 
 

Be prepared to change your plan….

[drapo]

I was there a couple of years ago and had to remind myself who would be benefiting from an engine overhaul vs cylinder change. The answer, although more costly, ended up being a major overhaul. Sure I spent some more money, more than double, but I'm the one flying the Mooney with a fresh engine 

 

[Raptor05121]

Replace the cylinders. My engine has 2400SMOH and I elected to replace two cylinders with bad blow by. We inspected the interior of the engine and everything was beautiful, oil analysis are great- I'm pushing it to 3,000

[skykrawler]

The problem you will have with getting an overhaul now with new cylinders is the unavailability of the cylinders.   I'm living that right now - waiting for cylinders.  Fortunately I didn't pull the engine yet.

[TheAv8r]

2 hours ago, skykrawler said:

The problem you will have with getting an overhaul now with new cylinders is the unavailability of the cylinders.   I'm living that right now - waiting for cylinders.  Fortunately I didn't pull the engine yet.

Ah, did not know supply issues had hit cylinders too, good to know. I'm planning to just OH the existing ones (if we can) vs. buying new for now, I'll buy all new when we do a full OH.

11 hours ago, Raptor05121 said:

Replace the cylinders. My engine has 2400SMOH and I elected to replace two cylinders with bad blow by. We inspected the interior of the engine and everything was beautiful, oil analysis are great- I'm pushing it to 3,000

Thanks! That's the plan, OH the 2 problem cylinders, inspect the engine to make sure everything looks good and healthy and then OH it when it's ready.

13 hours ago, drapo said:

I was there a couple of years ago and had to remind myself who would be benefiting from an engine overhaul vs cylinder change. The answer, although more costly, ended up being a major overhaul. Sure I spent some more money, more than double, but I'm the one flying the Mooney with a fresh engine 

 

Eh, to each their own. I don't like to Overhaul just to Overhaul, it's a rather expensive path. Look at it this way, if you have the money to overhaul the engine, and you know you're going to overhaul it when it shows the signs it's ready, then every hour you put on it between now and then is free time. Overhauling it early just to fly it with a fresh engine wastes all that time that was left on the engine. For example, right now my engine is showing no signs of needing an overhaul, just some cylinders are worn out. If while replacing the cylinders we see signs the bottom end is done then we will overhaul but if not, I might be able to get another 3 or 500 hours out of this engine before needing to overhaul it. That's 1/5 of the life of an engine I'd be throwing away if I just overhauled it now.

[MBDiagMan]

On 12/17/2021 at 6:11 PM, Bartman said:

I had an oil leak and thought it was a bolt that went thru the case. We pulled cylinders in anticipation of reconditioning and reinstalling, but the single worn cam lobe changed all of that. The subsequent discovery of the cracked case which was the cause of the oil leak was not expected. 
 

Be prepared to change your plan….

Yes, going into an engine is exploratory surgery.  You can’t know until you open it up.  In the case of the OP though, it is highly likely that cylinder removal and careful inspection prior to seeing to the cylinders will produce the desired results.

[M20F]

On 11/29/2021 at 2:58 PM, jaylw314 said:

I thought the IO-360 cylinders are about twice as expensive as other cylinders, like around $2k each? 

Wide deck are twice as much as a narrow deck roughly.  360’s can use either, Mooney used both, somebody will jump in and provide further details.  
 
You can spend as much as you want on anything.   My opinion is if it isn’t broke don’t fix it.  

[Igor_U]

Hmm,

I think you are referring to Angle valve cylinders in IO360 (200HP) vs parallel valve cylinders in O360 (180HP). BTW, there are also parallel vale IO360 (180HP) as installed in C172SP.

Narrow Deck (ND) engine are older and sometime in mid 60-s replaced by WD engines. My 67 M20F (built in October of 1966) already had original WD engine. To my understanding difference is in thickness of cylinder flange; same time accessory case is slightly different and the camshaft as well. Don't even ask why I know that...  

For OP, S/n number and/or call to Lycoming or competent engine shop will tell what he has... I really don't remember if ND cylinders are available as my original engine was WD... 

[Prior owner]

I’m still having trouble believing you might have busted ring(s)…. Burning only a quart of oil every 7 hours with a broken ring seems unlikely. But I’ve seen stranger things, I guess.

 

[Edit] whoops, I missed the final verdict! Glad to hear you’re not facing anything too harrowing!