bad cylinder

[Ulysse]

this is probably a stupid question, but how do you know a cylinder needs replacement?

Also, how do you determine you need a top overhaul? (what is a top overhaul anyway?)

Are these needs indicative of bad handling or just normal statistical wear ?

If it is poor handling, then, does the fact of having replaced one or more cylinders indicative of potential issues with other parts of the engine? 

Actually, I realize these are more than one (stupid) questions

[Mooneymite]

On 3/19/2022 at 3:14 AM, Ulysse said:

this is probably a stupid question, but how do you know a cylinder needs replacement?

I'm not an A&P, but most owners become aware of a bad cylinder through a compression check, or oily plugs.

The compression check can be a very slippery test and by itself, may mean very little except that it needs to be done again after flying.  Air may be leaking through the rings (listen to the oil sump through the oil fill hole), or through the valves (listen through the muffler outlet).

Oily plugs can indicate bad rings (particularly the oil scrapper ring), or just a plumb worn out cylinder.  But sometimes an oily plug can mysteriously fix itself....speculation is that the ring gaps aligned for no particular reason.

Even though you ask about a "cylinder", the symptoms can usuallly be addressed by lappping (rope trick), or regrinding valve seats, or repalcing valves. new rings, or miraculous incantations accompanied by Magic Mystery Oil, or some other elixir.  MIke Bush did an article cautioning us all about removing cylinders prematurely without throrough trouble shooting.  He also cautioned about the dangers of an improperly installed repaired/restored/replacement cylinder.  Sometimes an improperly replaced jug will cause a plethora of new problems.  https://www.aopa.org/news-and-media/all-news/2020/march/pilot/savvy-maintenance-risky-business

A big danger sign that usually does not have a simple/cheap fix is evidence of a crack in the cylinder evidenced usually by oil coming from an unusual location.....

I'll be interested to hear how the real mechanics answer your questions.

 

 

 

Edited March 23, 2022 by Mooneymite

[EricJ]

9 hours ago, Ulysse said:

this is probably a stupid question, but how do you know a cylinder needs replacement?

Also, how do you determine you need a top overhaul? (what is a top overhaul anyway?)

Are these needs indicative of bad handling or just normal statistical wear ?

If it is poor handling, then, does the fact of having replaced one or more cylinders indicative of potential issues with other parts of the engine? 

Actually, I realize these are more than one (stupid) questions

Unless there are issues indicating something needs to be done, then nothing needs to be done.   Issues might include running rough, excessive oil use, lack of power or other problems.    A compression check or borescope inspection might indicate problems without any noticeable operational issues, so those are potential reasons to do something as well.

Are you having any problems that might lead you to believe you need a cylinder change?

BTW:  It's not a stupid question.  

Edited March 19, 2022 by EricJ

[Ulysse]

10 minutes ago, EricJ said:

Are you having any problems that might lead you to believe you need a cylinder change?

No, I am thinking of buying another plane which has had 2 cylinders replaced, so I am wondering if this indicates future problems with the engine

 

11 minutes ago, EricJ said:

BTW:  It's not a stupid question

Thank you!

[Marauder]

Thank you!

I’ve gone through a cylinder replacement on my mid time engine. The fact the cylinders were replaced on this plane is a good sign. It means the owner is doing maintenance.

When you do the pre-purchase, just make sure they do a thorough inspection of the engine.


Sent from my iPhone using Tapatalk Pro

[philiplane]

9 hours ago, Ulysse said:

this is probably a stupid question, but how do you know a cylinder needs replacement?

Also, how do you determine you need a top overhaul? (what is a top overhaul anyway?)

Are these needs indicative of bad handling or just normal statistical wear ?

If it is poor handling, then, does the fact of having replaced one or more cylinders indicative of potential issues with other parts of the engine? 

Actually, I realize these are more than one (stupid) questions

More details needed. What engine are we talking about? How many hours and years since overhaul? Has the plane been sitting a lot? Or has it been flown a lot, by someone who doesn't mind the temperatures?

[EricJ]

43 minutes ago, Ulysse said:

No, I am thinking of buying another plane which has had 2 cylinders replaced, so I am wondering if this indicates future problems with the engine

It may not indicate anything about the rest of the engine.   The cylinders could have been changed due to burned valves or scored walls which doesn't indicate much about the rest of the engine other than it's not new.  A thorough inspection of the engine including compression test and borescope of all the cylinders is always a good idea.   If the previous owner has oil analysis history or engine monitor data, that can be useful in getting some insight into how the rest of the engine is doing.   

[Fly Boomer]

On 3/19/2022 at 2:14 AM, Ulysse said:

how do you know a cylinder needs replacement?

Read Mike Busch.  Especially with your Continental, compression alone is not a very good indicator.

[carusoam]

Let’s discuss the two normal modes that a TC’d Mooney gets operated in…

and what their expectations are for cylinder life…

1) Flown gently, LOP, for efficiency….

2) Flown ROP, in flaming dragon mode, for speed…

3) A combination of the two modes….

4) planes that don’t get flown often….

 

under the best circumstances… cylinders can go the distance of TBO…. Barely.

under the worst circumstances… cylinders can get used up before 1/2 way to TBO…

under a combination of the modes 1/2 way to TBO makes a lot of sense… balanced economics….

 

When checking the health of the cylinders…

People look at the valves for certain signs… pizza is good.

pics of the cylinder wall… cross hatches pattern is good.

 

Heat is the enemy… flying in fire breathing dragon mode costs extra cylinders… a normal cost of doing business… air cooling is harder to come by in the flight levels…

Replacing all of the cylinders at once… is called a top OH…

Repairing individual cylinders along the way… can happen…

 

Unflown planes suffer from oxidation issues… the cylinder walls is a place for that to occur… look for pits…

 

PP thoughts on what to look for and things to discuss with the prior owner…   Not a mechanic…

For fun… find the Acclaim owner with 2k+ on his cylinders(?) it’s an interesting conversation…

 

Best regards,

-a-

[Ulysse]

10 hours ago, carusoam said:

Replacing all of the cylinders at once… is called a top OH…

thank you. Now I know!

[DXB]

On 3/19/2022 at 12:25 PM, Ulysse said:

No, I am thinking of buying another plane which has had 2 cylinders replaced, so I am wondering if this indicates future problems with the engine

It does not.  Cylinders are finicky and fungible assets, albeit not cheap ones.  Their demise can come from running them too hot, too rich, too lean at high power settings, very subtle manufacturing defects, or for no discernable reason at all.  I suspect the most common absolute indication for cylinder IRAN, overhaul, or replacement is a visibly burnt exhaust valve, which portends an inexorable progression toward catastrophic failure. Massive blow by due to a broken ring would lead to the same. Either could lead to low static compression test results, but not necessarily.  Some decisions to change a cylinder are soft calls and must be weighed against the substantial risks of invasive maintenance.

Regardless, the decision to change a cylinder does not indicate anything is wrong with the bottom end of the engine, whose condition is the driver of major overhaul.  

Edited March 22, 2022 by DXB

[jaylw314]

On 3/19/2022 at 9:25 AM, Ulysse said:

No, I am thinking of buying another plane which has had 2 cylinders replaced, so I am wondering if this indicates future problems with the engine

Having 2 cylinders replaced doesn't say anything about the engine's history, but it is a concern in regards to replacing 2 cylinders at once--there are definitely wrong ways of doing it, so you would want it done by people who know how.  

[MARZ]

Kinda surprised I haven't seen oil consumption for an indicator of cylinder issues...... 

[Mooneymite]

26 minutes ago, MARZ said:

Kinda surprised I haven't seen oil consumption for an indicator of cylinder issues...... 

The oily plugs might be a "sooner indicator".  A big mag drop due to oil contaminated plugs, might spur further investigation.

[A64Pilot]

On 3/23/2022 at 4:13 PM, MARZ said:

Kinda surprised I haven't seen oil consumption for an indicator of cylinder issues...... 

it is obviously, but allowable oil consumption for a Lycoming is an astonishing amount

This is the formula 0.006 x BHP x 4 ÷ 7.4 = Qt./Hr.  So a 200 HP motor if I do the math correctly can consume .65 quarts an hour and be Airworthy, but you still have to pass compression tests

https://www.lycoming.com/sites/default/files/Lycoming Reciprocating engine Break-In and Oil Consumption.pdf

[Guest]

On 3/19/2022 at 3:14 AM, Ulysse said:

this is probably a stupid question, but how do you know a cylinder needs replacement?

Also, how do you determine you need a top overhaul? (what is a top overhaul anyway?)

Are these needs indicative of bad handling or just normal statistical wear ?

If it is poor handling, then, does the fact of having replaced one or more cylinders indicative of potential issues with other parts of the engine? 

Actually, I realize these are more than one (stupid) questions

The brand of engine has as much to do with cylinder replacement.  Continental engines as a general rule have crappy cylinders which seldom make TBO.  Lycoming cylinders are much more likely to make TBO.

Aftermarket cylinders have had spotty reputations, with many having ADs against them.

Clarence