Does this picture show corrosion/pitting in a cylinder?

[netsurfr]

My SAVVY Pre-Buy Experience. Corrosion/pitting in a cylinder debate?

I hired SAVVY (Mike Busch's company) to manage a pre-buy on a Piper Dakota. I got this borescope picture from SAVVY's A&P indicating this is heavy corrosion and pitting and that I should walk away from the plane and I have another A&P saying it's no cause for concern. I'm working on getting a 3rd opinion but in the mean time thought I'd check here...

https://www.dropbox.com/s/d66grl3l6n9wpfp/BK650052.JPG?dl=0

If it is heavy corrosion/pitting is re-honing a safe/good fix for this (assuming it's within specs and no corrosion is found in cam/lifters after pulling a cylinder)?

 

[Geico266]

The picture is too poor a quality to make a decision IMHO. I can see cross hatch of the honing so I would say fly it if the compression is good.

 

[netsurfr]

Thanks. I called Lycoming because this is all new to me and they said that they don't think a bore scope picture is to be relied upon to decide because they said most bore scope pictures are not good enough (quality) to really know for sure.

Question and I'm sure it's a dumb one but the A&P who doesn't see a problem here also said he sees cross hatch so that was good BUT I didn't ask him what that meant so why is seeing cross hatching good? Does that indicate something?

 

[Geico266]

Thanks. I called Lycoming because this is all new to me and they said that they don't think a bore scope picture is to be relied upon to decide because they said most bore scope pictures are not good enough (quality) to really know for sure.

Question and I'm sure it's a dumb one but the A&P who doesn't see a problem here also said he sees cross hatch so that was good BUT I didn't ask him what that meant so why is seeing cross hatching good? Does that indicate something?

Not a dumb question at all.

The cross hatching (see the picture) is caused by the honing scratching small imperfections into the cylinder walls. They will fill with oil as the piston goes up, and the wiping ring wipe the oil off on the way down leaving a small amount of oil in the cross hatching to lube the cylinder and piston. Metal to metal is not a good thing. The oil acts and a buffer between the piston, rings, and the cylinder wall. Obviously, there is still wear, but the cross hatching prolongs cylinder life a very long time over no cross hatching at all.

Even the angle of the cross hatching has been studied and refined.

https://www.hastingsmfg.com/ServiceTips/cylinder_bore_refinishing.htm

 

[netsurfr]

Ahh that makes total sense. So the cross hatching is something they put there on purpose to keep reduce that friction and as you run your engine over the years the x-hatching gets more and more worn off so less oil or if there was heavy corrosion it would be covering up the x-hatching I guess. That helps. Thanks!

 

[Geico266]

Ahh that makes total sense. So the cross hatching is something they put there on purpose to keep reduce that friction and as you run your engine over the years the x-hatching gets more and more worn off so less oil or if there was heavy corrosion it would be covering up the x-hatching I guess. That helps. Thanks!

Exactly!

This is why changing your oil is SO important! The oil filter can only filter out particles so fine. The rest is suspended in your oil and recycled through the engine over and over. The oil is spread very thin on these surfaces and provides lubrication, cooling, and çleaning.

 

[netsurfr]

Wow I would have never guessed that microscopic particles could do so much harm if you couldn't see them w/ your eyes but yeah makes total sense. At those speeds & temps I guess any tiny bit of something would create friction.

I've always changed oil in cars/motorcyles/etc... regularly but never thought about it this way. I figured it was more that you're chaning it cause it looses viscosity and accumulates dirt.

Thanks this actually educated me quite a bit. This (learning more about the engine/mechanic aspect) is something I'm working on getting better at.

 

[Geico266]

This is why a lot of airplane owners send in oil samples for analysis. It will show how much lead, iron, sand, brass, aluminum, etc. is in your oil and what the norms are for an engine. Very useful knowledge.

We should never ever stop learning, ever.

 

[netsurfr]

Very true!

This is why a lot of airplane owners send in oil samples for analysis. It will show how much lead, iron, sand, brass, aluminum, etc. is in your oil and what the norms are for an engine. Very useful knowledge.

We should never ever stop learning, ever.

 

[Dan Thomas]

Ahh that makes total sense. So the cross hatching is something they put there on purpose to keep reduce that friction and as you run your engine over the years the x-hatching gets more and more worn off so less oil or if there was heavy corrosion it would be covering up the x-hatching I guess. That helps. Thanks!

Wrong. The crosshatching is there to make sure the piston rings and cylinder walls wear at each other fairly aggressively early in the engine's life. Neither the rings nor the cylinder are anywhere near perfectly round and do not seal worth a hoot until that wear takes place. The rings themselves are machined with either a beveled outside edge so that the bottom edge is against the cylinder wall at first as opposed to the whole side of the ring, or there's a bevel machined into the inside top edge of the ring to make it twist once it's compressed in the cylinder, putting that bottom edge into contact with the cylinder. Some rings have both, and both are there to cause rapid seating of the ring against the cylinder wall. Breaking in an engine involves running it fairly hard the first few hours to put extra pressure behind those rings and force them to mate with the cylinder wall.

The initial crosshatch depth is critical. It's measured in microinches (millionths of an inch) and controlled by the size of grit in the honing stones and the pressure on those stones. If the crosshatch too shallow the cylinder could glaze too soon and the seating stops before the rings and cylinders are completely mated, and the engine will have poorer compression and use more oil. Running a new engine timidly will do the same thing. If that crosshatch is too deep the wear is too aggressive and too much of the rings disappear and too much oil is left in that crosshatch and the engine will use more oil. A rough crosshatch gets sizeable bits of iron torn off that score the cylinder vertically. Not good.

Lots of old engines have no crosshatch left and run just fine. There is always a microscopic surface roughness that will hold enough oil for lubrication, and rings actually need very little oil compared to the rod and main bearings. Worn bearings have larger clearances and throw more oil at the cylinder walls and can flood them and cause oil burning.

Dan

 

[Stache]

Jose it is my opinion, but I would highly recommend you have the cylinder pulled and a proper inspection accomplished. I have accomplished a lot of borescope inspections there is only so much you can tell. Maintenance manuals state the best inspection is to remove the cylinder and look. While it is off they can check the valve seats and perform a full measurement check to see if rehoning the cylinder will clean it up. Looking at the picture is enough for me to pull the cylinder jug as it will not take that long. Better safe pulling them now it and may safe them verse having to replace them later if it is pitting corrosion and you start burn lots of oil.

 

[Henning]

Meh, why pull the cylinder before failure? With the cross hatch I see left there, you'll be able to start and run the engine cleaning any corrosion off and get a good seat back to the rings. If it doesn't work out, all that will happen is you have high oil consumption and you can deal with it then. It's not going to cause you to fall out of the sky. I have taken completely seized up 6-71 Detroits, poured some juice in down the injector ports, broke them loose with a pipe wrench, started them and drove them 1500nm no worries.

What you are looking at is next to nothing which is why nobody can make the call. Run the engine, do an oil analysis, run some more, do another, report the results.

 

[kmead]

Looks like typical corrosion that I see on many TIO540 cylinders at pre-buys and annuals. I wouldn't do anything unless you have high oil consumption.

 

[Henning]

Is this a pre purchase inspection or are you doing maint on a plane you own?

 

[netsurfr]

Guys thanks. This was something found on a pre-buy and I have one A&P saying this is major corrosion and pitting and should walk away and another A&P saying it's not so not sure who to believe.

 

[Henning]

Guys thanks. This was something found on a pre-buy and I have one A&P saying this is major corrosion and pitting and should walk away and another A&P saying it's not so not sure who to believe.

It's not cylinder corrosion I'd be concerned with, cost of that is very limited to repair, you can negate out the price of a jug easy, and I doubt that needs it. If it's a Lycoming I'd be more interested in what the cam looks like, that gets more expensive, but the entire engine isn't that big of a deal when compared to Airframe corrosion; THAT is what you want to be searching deep for.

 

[netsurfr]

Yes I agree on airframe corrosion and we will find out when airframe inspection happens but for right now I've put a stop to the pre-buy and want to focus on the cylinders so what I'm asking is you all agree that this picture shows heavy corrosion and pitting and if so would removing a (middle #3 or #4) cylinder be an acceptable way to inspect the cam and lifters on a o-540 lycomings.

 

[Henning]

Yes I agree on airframe corrosion and we will find out when airframe inspection happens but for right now I've put a stop to the pre-buy and want to focus on the cylinders so what I'm asking is you all agree that this picture shows heavy corrosion and pitting and if so would removing a (middle #3 or #4) cylinder be an acceptable way to inspect the cam and lifters on a o-540 lycomings.

No, I see light corrosion that will go away when you run the engine with no great consequence from what is left behind. The only worry you have in those cylinders is some extra oil consumption.

 

[netsurfr]

Thanks. I'm in a tough spot. I have one A&P (hired by SAVVY) saying this is heavy corrosion and pitting and the seller's A&P disagreeing. Compressions were all in the 70's except 1 cylinder at 68. Oil analysis shows no issues and oil and filter inspection revealed no issues.

No, I see light corrosion that will go away when you run the engine with no great consequence from what is left behind. The only worry you have in those cylinders is some extra oil consumption.

 

[Henning]

Thanks. I'm in a tough spot. I have one A&P (hired by SAVVY) saying this is heavy corrosion and pitting and the seller's A&P disagreeing. Compressions were all in the 70's except 1 cylinder at 68. Oil analysis shows no issues and oil and filter inspection revealed no issues.

I wouldn't sweat it then. If the jug starts using a bunch of oil, then you might want to do something. What is of more concern to me when I see that jug is the cam. What is the engine?

 

[netsurfr]

What about the jug gives you concerns about the cam? It's a Lycomings O-540. Plane is in Dallas and has been flown an average of 30 hours / year for the last 4 so little flying time. Seller is willing to pay his A&P to pull a cylinder and have my A&P inspect cylinder & use a bore scope to see the cam. I thought that sounded like a good way to find out but SAVVY is saying otherwise.

I wouldn't sweat it then. If the jug starts using a bunch of oil, then you might want to do something. What is of more concern to me when I see that jug is the cam. What is the engine?

 

[Henning]

What about the jug gives you concerns about the cam? It's a Lycomings O-540. Plane is in Dallas and has been flown an average of 30 hours / year for the last 4 so little flying time. Seller is willing to pay his A&P to pull a cylinder and have my A&P inspect cylinder & use a bore scope to see the cam. I thought that sounded like a good way to find out but SAVVY is saying otherwise.

What does the SAVVY dude have against that idea? What does he want to do? Just walk away? I don't know the rest of the plane, I don't know anything about the deal, but from that jug picture alone I wouldn't be walking away from a clean airframe with good radios. Was the plane hangared?

I'm trying to understand the SAVVY dude's angle.

 

[gismo]

Wow I would have never guessed that microscopic particles could do so much harm if you couldn't see them w/ your eyes but yeah makes total sense. At those speeds & temps I guess any tiny bit of something would create friction.

I've always changed oil in cars/motorcyles/etc... regularly but never thought about it this way. I figured it was more that you're chaning it cause it looses viscosity and accumulates dirt.

Thanks this actually educated me quite a bit. This (learning more about the engine/mechanic aspect) is something I'm working on getting better at.

AFaIK, as long as the particle size is less than the bearing and ring clearance (i.e. the thickness of the oil layer between metal) there's no significant extra wear due to the particle contamination.

 

[netsurfr]

Things have gotten quite weird w/ SAVVY on this. They are hell bent that I should walk away and they are completely opposed to letting the owner's A&P pull the cylinder to inspect. There were some other squawks found but owner was willing to take care of airworthiness items so not sure why SAVVY wants me to walk. They are not giving me a solid opinion other than the a&P they recommended found corrosion/pitting in cylinders.

Plane has been hangared and annuals done and owners have put a lot of money into it in the last 5 years (new paint, new interiors, new panel with Aspen 1000 Pro, Aspen 500 MFD, JPI 830, century 2K auto pilot w/ auto trim, dual 430Ws to name a few).

I have a choice to make. Either do what SAVVY says (walk away) or hire another A&P and pay that guy for a second pre-buy to see if they agree.

What does the SAVVY dude have against that idea? What does he want to do? Just walk away? I don't know the rest of the plane, I don't know anything about the deal, but from that jug picture alone I wouldn't be walking away from a clean airframe with good radios. Was the plane hangared?

I'm trying to understand the SAVVY dude's angle.

 

[Silvaire]

Are you telling us that Savvy is making the decision to walk away based on that picture alone?

For one thing that is not a borescope, it's one of those video-scope tools with maybe 640x480 res at best but probably 320x240. Good for reading the serial numbers on a hard to see magneto dataplate but virtually worthless for examining cylinders. If someone is making calls based on that picture I'd find a new consultant.

 

[flyingmoose]

Yea I agree. Why would they be opposed to them pulling it for inspection? That pic is not good and I wouldn't completely walk away, unless they know something else that you are not mentioning.

 

[netsurfr]

That is exactly what's happening. They said that they agree with the A&P they recommended to do the prebuy and that this bore scope image (they told me this is a really good bore scope the A&P used) shows major corrosion and pitting and that I should walk way. They simply say that under no circumstance should the sellers A&P be allowed to do anything to the plane either. There were other squawks and I'll post them but according to them they weren't deal killers just a lot of little things. They are giving me no other reasons than what I've written.

Are you telling us that Savvy is making the decision to walk away based on that picture alone?

For one thing that is not a borescope, it's one of those video-scope tools with maybe 640x480 res at best but probably 320x240. Good for reading the serial numbers on a hard to see magneto dataplate but virtually worthless for examining cylinders. If someone is making calls based on that picture I'd find a new consultant.

 

[netsurfr]

Here's the list of squawks...

*Boroscope inspection revealed moderate to heavy cylinder wall corrosion on every cylinder.
(Easily $ 0000+ for cylinder removal, repair, and installation, if no other issues are found during
process.)

*Tach needle bounces. ($400 plus install labor)

*Yokes are stiff (Will require further investigation, maybe a couple of hours to ID cause of issue,
then additional to repair)

Mixture lock tab doesn't work ($200ish for new cable plus install labor)

Prop cable attachment pin and socket are loose, worn out. ($ 00 parts plus labor)

*#2 oil return line chafe mark exceeding 20%

*Starter and flywheel ring gear have damaged teeth. (Starter $500, ring gear $250, plus labor)

#4 primer line chafing against the cylinder fins.

R/H aft baffle is loose, all screw connections are pulling through the baffle or have elongated the
original mount holes. ($200-400 to repair)

Front R/H baffle isn't secure ($ 00-200 to repair)

Front L/H baffle is torn and needs repair. ($50 to repair seal)

# primer line needs replacement, deep nick in the line.

All motor mounts are sagging, bottom mounts have gaps due to excess sag. ($800 parts 4 hours
labor)

Flammable fluid carrying hoses are over 0 years old. ($700- 000 parts)

Check skin distortion below windshield, pilot side.

Oil return hoses leaking.

Oil on the bottom of the engine, possible oil leaks, engine is too dirty to identify sources.

Landing light doubler fell out of the engine compartment when we removed the cowl.

*Mag drop above spec on both side, L 80 R 70 drop.

L/H side of the heat exchanger shroud is breaking off, there are other cracked areas of the shroud
as well.

R/H steering rod end is worn.

 

[netsurfr]

No good reason for not allowing sellers A&P to do the cylinder pulling other than they said we'd lose control of the prebuy if we allow sellers A&P to work on plane and other reason was given the squawks identified and given the A&P signed off the plane with these squawks at last annual he can't be trusted.

Yea I agree. Why would they be opposed to them pulling it for inspection? That pic is not good and I wouldn't completely walk away, unless they know something else that you are not mentioning.

 

[Silvaire]

...(they told me this is a really good bore scope the A&P used)...

They're full of it right there - that is NOT a Borescope, it's a cheap a$$ Chinese button camera on the end of a flexible stick. I know because I've got two of them. They are great for certain things but this ain't one of them.

I have no personal experience or beef with Savvy but I have observed that it seems like Mike Busch has developed a big business out of convincing folks that every A&P Mechanic is out to screw you. I have noticed that the members often exhibit behavior akin to a cult and so I usually try to avoid them as much as possible.

 

[Henning]

Things have gotten quite weird w/ SAVVY on this. They are hell bent that I should walk away and they are completely opposed to letting the owner's A&P pull the cylinder to inspect. There were some other squawks found but owner was willing to take care of airworthiness items so not sure why SAVVY wants me to walk. They are not giving me a solid opinion other than the a&P they recommended found corrosion/pitting in cylinders.

Plane has been hangared and annuals done and owners have put a lot of money into it in the last 5 years (new paint, new interiors, new panel with Aspen 1000 Pro, Aspen 500 MFD, JPI 830, century 2K auto pilot w/ auto trim, dual 430Ws to name a few).

I have a choice to make. Either do what SAVVY says (walk away) or hire another A&P and pay that guy for a second pre-buy to see if they agree.

This is strange, makes me wonder if he wants the plane or something. If you don't want to discuss the details of the deal in the open, I'd appreciate a PM, something is missing from this whole picture.

 

[Dr. O]

Take a deep breath.
Savvy is backing the opinion of their 'expert'. They don't have a choice. If they buck the 'expert' and the engine subsequently turns out to be a dog, they have liability and reputation loss.

Now, a few light corrosion pits in the cylinder is not a major issue, other than it will wear the rings sooner. And if this was already your plane I would say just run it until you get tired of pouring expensive oil down the tube.
But the real issue on a new purchase is the cam. Even light pitting can become real expensive real soon.
So here is what I would do if it were my nickle.
Pull the jug. The upside is that you (your expert) get to visually inspect it, drag a fingernail across it, etc. Also you get a look at the rings, the piston skirts and so on.
Further, a real borescope, not a faux scope with a low resolution video screen, but one with visual optics can now be used to peer up at the cam and get a look at the int/exh lobes for that cylinder while it is slowly rolled through all four strokes.
I won't bore you with a long description of how I make judgements about the condition of the lobes - your experts can help you with that.

There is a branching decision tree you need to go through to make a final decision. But let me get to just the one branch I consider crucial. Let's assume you find the two cam lobes to be pristine and the corrosion in the jugs to be minor and you intend to purchase.
1. You can throw the jug back on and assume everything will be fine
2. You can send all the jugs out for an overhaul and fresh rings
3. You can hang new jugs

1 - I would not
2. Is probably the best option at the least cost - assuming these are first run jugs. If they are second run, fergeddaboutit
3. Is what I would do - but that's just me after owning, fixing, and cursing, over more jugs than I can remember

The issue with the big engines is not so much the condition of the bore as it is the exhaust valve and rocker arm bushings. Not many will run to/near TBO without having had the valves overhauled at least once. This engine already has hours on the top end. You have a golden chance here to have a solid top end that will run for as long as you own the plane (likely, based on average 5 - 7 year cycle)
And fresh jugs will add how much to the cost of buying and operating the plane for 7 years, as a percentage of total cost. Not much.

cheers

 

[Henning]

Yeah, exactly, let them pull the jug and then you can get a proper visual on everything. If the owner is willing to go this far, if it's decided the cam and jug need replacing, give him the chance to do so.

The SAVVY dude is sounding unreasonable in the real world.

 

[netsurfr]

OK thanks guys. This is a my first plane so this makes things even harder but so far everyone I've asked seems to be thinking SAVVY's recommendation to simply walk away is extreme and unwarranted but yes they are making their opinion solely on what the A&P they hired said.

Now here's where I'm still worried now... Seller has agreed to pay to have a cylinder pulled for further inspection. Additionally he said if the cylinders are found to need honing he'd pay and of course if corrosion is found in the cam then he understand that would be an even bigger problem. The concerns/fear I have is SAVVY said taking cylinders out to inspect or fix is a HUGE risk they don't recommend taking because of the potential for bearing shift (don't know what that is but sounds bad) so now I'm scared of having the cylinders removed for re-honing if that's what it takes to fix it.

This engine was overhaulded by Poplar Grove in 2001 and has had 960 SMOH btw.

 

[netsurfr]

What's the price difference between overhauling jugs and new rings vs. new? Also isn't risky to pull out all jugs at the same time?

Take a deep breath.
Savvy is backing the opinion of their 'expert'. They don't have a choice. If they buck the 'expert' and the engine subsequently turns out to be a dog, they have liability and reputation loss.

Now, a few light corrosion pits in the cylinder is not a major issue, other than it will wear the rings sooner. And if this was already your plane I would say just run it until you get tired of pouring expensive oil down the tube.
But the real issue on a new purchase is the cam. Even light pitting can become real expensive real soon.
So here is what I would do if it were my nickle.
Pull the jug. The upside is that you (your expert) get to visually inspect it, drag a fingernail across it, etc. Also you get a look at the rings, the piston skirts and so on.
Further, a real borescope, not a faux scope with a low resolution video screen, but one with visual optics can now be used to peer up at the cam and get a look at the int/exh lobes for that cylinder while it is slowly rolled through all four strokes.
I won't bore you with a long description of how I make judgements about the condition of the lobes - your experts can help you with that.

There is a branching decision tree you need to go through to make a final decision. But let me get to just the one branch I consider crucial. Let's assume you find the two cam lobes to be pristine and the corrosion in the jugs to be minor and you intend to purchase.
1. You can throw the jug back on and assume everything will be fine
2. You can send all the jugs out for an overhaul and fresh rings
3. You can hang new jugs

1 - I would not
2. Is probably the best option at the least cost - assuming these are first run jugs. If they are second run, fergeddaboutit
3. Is what I would do - but that's just me after owning, fixing, and cursing, over more jugs than I can remember

The issue with the big engines is not so much the condition of the bore as it is the exhaust valve and rocker arm bushings. Not many will run to/near TBO without having had the valves overhauled at least once. This engine already has hours on the top end. You have a golden chance here to have a solid top end that will run for as long as you own the plane (likely, based on average 5 - 7 year cycle)
And fresh jugs will add how much to the cost of buying and operating the plane for 7 years, as a percentage of total cost. Not much.

cheers

 

[Henning]

OK thanks guys. This is a my first plane so this makes things even harder but so far everyone I've asked seems to be thinking SAVVY's recommendation to simply walk away is extreme and unwarranted but yes they are making their opinion solely on what the A&P they hired said.

Now here's where I'm still worried now... Seller has agreed to pay to have a cylinder pulled for further inspection. Additionally he said if the cylinders are found to need honing he'd pay and of course if corrosion is found in the cam then he understand that would be an even bigger problem. The concerns/fear I have is SAVVY said taking cylinders out to inspect or fix is a HUGE risk they don't recommend taking because of the potential for bearing shift (don't know what that is but sounds bad) so now I'm scared of having the cylinders removed for re-honing if that's what it takes to fix it.

This engine was overhaulded by Poplar Grove in 2001 and has had 960 SMOH btw.

How close are you to Poplar Grove now to let them take over the engine work, and will the seller agree to this. Personally at this point I would fire the SAVVY guy based on what you have posted here. He's either a kook or has an agenda, either way His actions give me a bad vibe.

The seller you are dealing with sounds reasonable, all his actions so far have been on par with how deals should go.

 

[netsurfr]

Well I live in WI but plane is in TX so not sure how this would work.

How close are you to Poplar Grove now to let them take over the engine work, and will the seller agree to this. Personally at this point I would fire the SAVVY guy based on what you have posted here. He's either a kook or has an agenda, either way His actions give me a bad vibe.

The seller you are dealing with sounds reasonable, all his actions so far have been on par with how deals should go.

 

[cujet]

Note: You can see a portion of the cylinder bore by simply looking in the spark plug hole, using a bright light. Better yet, use a small light on the end of a wand and insert it in the hole to illuminate the cylinder.

Note #2: Borescopes of any sort can make microscopic flaws look huge.

Note #3: We have constant cylinder corrosion issues here in South Florida. As long as the pitting is relatively minor in nature, the engine is operated regularly and oil consumption is reasonable, we experience no problems.

 

[netsurfr]

cujet - Thanks for that info. So far all the googling I've been doing on corrosion & cylinder pitting seems to indicate that it's not something that means the engine and/or plane should be condemened. I read a lot about oil analysis, oil & filter checking, compressions and ultimately pulling a jug to take a look and even if corrosion & pitting is found there are degrees of it and can be fixed w/ solutions ranging from re-honing to on the other end overhauling.

Today I will be calling a couple A&P in TX to see about getting a second opinion and doing another pre-buy. I just don't trust SAVVY and their A&P right now so need someone else to step in.

 

[Henning]

I think that's a wise plan. Where in TX? There are many people on this board from all over TX that can help steer you at someone good.