Houston we have a [dead cylinder].

[Ragsf15e]

12 hours ago, wingtipwalker said:

The lifter “collapsed”...To be totally honest I’m not comfortable with the mechanics of what that means. But (I’m told) there was not the tell-tale metal on metal tapping sound I’m told is a bad sound when you’re dealing with unhealthy lifter-to-cam lobe impact. 

Mechanic said he would inspect the cam to make sure there wasn’t any damage. 

While he’s got the cylinder off, have him look and take pictures of all the cam/lifters he can see just like @Bartman picture above.  You can see the pitting on that lifter right now even before the cam has worn down.  

This is a separate problem from your stuck valve, but pitted lifters and worn cam lobes are happening to a lot of us and the only ways to see it is with a cylinder off or by measuring valve travel inside a cylinder but by then the cam is toast.

[Tcraft938]

4 hours ago, Ragsf15e said:

While he’s got the cylinder off, have him look and take pictures of all the cam/lifters he can see just like @Bartman picture above.  You can see the pitting on that lifter right now even before the cam has worn down.  

This is a separate problem from your stuck valve, but pitted lifters and worn cam lobes are happening to a lot of us and the only ways to see it is with a cylinder off or by measuring valve travel inside a cylinder but by then the cam is toast.

What causes the cam pitting?  Is it lack of engine use?  Improper oil?  Combination?   I should have asked that question at OH when I was told/showed pitting on my cam, so new was installed.  Thanks

[N201MKTurbo]

7 minutes ago, Tcraft938 said:

What causes the cam pitting?  Is it lack of engine use?  Improper oil?  Combination?   I should have asked that question at OH when I was told/showed pitting on my cam, so new was installed.  Thanks

 

 

The picture above shows lifter spalling.

There is a lot of opinions on that.

Some think it is corrosion.

The research I've done suggests that it is sub surface micro cracks caused by impact forces.

The pitting on the cam lobes is a bit harder to explain, but if it was corrosion why are the pits only on the peaks? They seem like spalling too.

[Ragsf15e]

7 minutes ago, Tcraft938 said:

What causes the cam pitting?  Is it lack of engine use?  Improper oil?  Combination?   I should have asked that question at OH when I was told/showed pitting on my cam, so new was installed.  Thanks

Im no mechanic and there will be someone else by to explain it better, but the general consensus seems to be disuse that allows the oil to come off the lifters and then they start corroding.  Since they are designed to slide on the cam, any irregularities allow the cam to get ground down.  Possibly some metallurgy issues as well...

[Ragsf15e]

4 minutes ago, N201MKTurbo said:

 

 

The picture above shows lifter spalling.

There is a lot of opinions on that.

Some think it is corrosion.

The research I've done suggests that it is sub surface micro cracks caused by impact forces.

The pitting on the cam lobes is a bit harder to explain, but if it was corrosion why are the pits only on the peaks? They seem like spalling too.

I agree and defer to your knowledge on this.  My only addition is that the peak on the cam is where the lifter is pushing hardest on the cam (spring fully depressed).  Any chance the peak of the cam gets worn first and then starts corroding there?

[N201MKTurbo]

11 minutes ago, Ragsf15e said:

I agree and defer to your knowledge on this.  My only addition is that the peak on the cam is where the lifter is pushing hardest on the cam (spring fully depressed).  Any chance the peak of the cam gets worn first and then starts corroding there?

Possibly,

I believe the cams are case hardened, either by carburizing or nitriding. If you wear through this layer, the wear rate will increase.

Also the stresses are higher at the tips, so if the spalling is caused by subsurface stress cracking, that's where it would happen.

None of us are cam and lifter engineers, so we can speculate all we want, but the only thing we can do is replace them when they get bad enough.

https://www.researchgate.net/publication/328305584_Prediction_of_Sub-Surface_Crack_and_Spall_Formation_on_Spur_Gear_Teeth

http://staging.uniones.com/technical_manuals/Cast/III.C.Contact stress spalling Rev6.pdf

https://evolution.skf.com/us/the-progression-of-surface-rolling-contact-fatigue-damage-of-rolling-bearings/

https://www.asminternational.org/documents/10192/1849770/06197G_Sample_BuyNow.pdf/2f15ca46-5605-4688-997a-c6f2d138829a

https://www.diva-portal.org/smash/get/diva2:8776/FULLTEXT01.pdf

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.921.2846&rep=rep1&type=pdf

 

[Ragsf15e]

21 minutes ago, N201MKTurbo said:

Possibly,

I believe the cams are case hardened, either by carburizing or nitriding. If you wear through this layer, the wear rate will increase.

Also the stresses are higher at the tips, so if the spalling is caused by subsurface stress cracking, that's where it would happen.

None of us are cam and lifter engineers, so we can speculate all we want, but the only thing we can do is replace them when they get bad enough.

https://www.researchgate.net/publication/328305584_Prediction_of_Sub-Surface_Crack_and_Spall_Formation_on_Spur_Gear_Teeth

http://staging.uniones.com/technical_manuals/Cast/III.C.Contact stress spalling Rev6.pdf

https://evolution.skf.com/us/the-progression-of-surface-rolling-contact-fatigue-damage-of-rolling-bearings/

https://www.asminternational.org/documents/10192/1849770/06197G_Sample_BuyNow.pdf/2f15ca46-5605-4688-997a-c6f2d138829a

https://www.diva-portal.org/smash/get/diva2:8776/FULLTEXT01.pdf

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.921.2846&rep=rep1&type=pdf

 

One other thing we can do is try something new.  DLC lifters might help if we’re already in there replacing the cam, but we don’t have long term data.  Roller lifters make sense too but you gotta get a factory engine to get them.  

[jetdriven]

You can buy my IO360 roller case and you can get it that way to. 
But there is long-term data on DLC lifters, they’ve been out in service now for a few years, and really nobody’s reporting failures at all. Quite remarkable

[carusoam]

In case you don’t recognize the things in Bart’s pics above...

I put some numbers on it...

For things to look for...

Its all about cams and cam followers... the two surfaces that slide against each other...

When the cam follower gets craters... oil no longer forms enough film to lubricate the two....

The cam’s case hardened surface isn’t thick enough to outlast the craters....

It can take about 100 hours of flight, over a year, to turn that full lobe into more of a nub...

1) Shiny worn spot from contact with the follower... the follower is impacting the surface, without enough lubrication... Excess wearing is probably starting to show... oil testing will start showing elevated levels of cam lobe...

2) Shiny smooth look of a good lobe, its follower’s surface is hidden in the picture...

3) Early signs of a cratered follower... the important center of the follower is looking pretty healthy,  if you can get this out... now would be the time to do it..(?)

4) Oddity of images and oily shined surfaces... could be a reflection of the rough cast surface of the case...
 

After my stuck valve experience, and replacement of the cylinder.... you could hear the odd tappet of three like cylinders, and one odd ball...   click, click, click, clack...
 

It is believed to be corrosion that causes the cam lobes to go missing... Engines that get flown often don’t have this challenge... engines that sit, suffer the most...

It may be a misnomer... but the craters look similar to inter granular type corrosion where the corrosion creeps into the metal structure and weakens and releases the surface above... Whole granules of metal have gotten freed up...

PP thoughts only, not a mechanic... Or metallurgist...

Best regards,

-a-

[the_elkhartian]

So update. Local engine shop wasn’t sure that they could use oversized valve seats to rebuild my cylinder. They’re building up a new stud assembly and reusing my piston with new rings for about $1200. The new cylinder is nitrided (unlike the others that are chromed). Everybody seems to agree that  mixing and matching is no big deal. 
 

Hoping it’s all put back together this week! Weather is turning nice in AZ I need to be flying my Mooney and not just these boring Pipers and Diamonds!

[jetdriven]

How much cheaper is this than a brand new factory Lycoming Nitrided cylinder?

[Ragsf15e]

1 hour ago, jetdriven said:

How much cheaper is this than a brand new factory Lycoming Nitrided cylinder?

My cylinder experience has been close to 50% cheaper for overhauled.  The angle valve cylinders are expensive!  Maybe less savings on other cylinders?

[the_elkhartian]

15 hours ago, jetdriven said:

How much cheaper is this than a brand new factory Lycoming Nitrided cylinder?

$2200 for factory new. So about $1000 less. 
 

Overhauled would seem to be the obvious choice on my “high-time” (1500 hours) engine. 

[jetdriven]

But you’re not getting your cylinder back, right? I think the economics of overhauling your first run cylinders are pretty good, but if you get somebody’s 8000 hour cylinder I’m not sure if there’s any economy there. Now you have a 1500 hour engine and that also sways it in favor of that as well

[the_elkhartian]

Captain’s Log....6 weeks AOG and still no resolution. 
 

So, if you recall, I had a dead cylinder 1 and a dead cylinder 3. Shop did a compression check hot and I still had a dead cylinder 1 and #3 came back to life. 
 

New (Overhauled) #1 has been installed and when the mechanic did a ground run he said that it was shaking violently at idle RPM settings and then when he got up to around 1200 rpm it smoothed out. 
 

He took it back in and had no compression on #3 cylinder. Scoped the number 3 and he noted some heavy buildup of carbon under the exhaust valve but otherwise looks okay. 
 

He wanted to check the lifters and I just got a text at the end of the day saying, “There a 3 lifters not holding pressure, and i one pushrod i am not sure about.  I can show you, still doesnt explain low compression in #3 though.”

Im starting to lose faith in this shop. I feel like they’re doing exploratory surgery. I also feel like they’re really busy with other higher margin projects and he’s stalling me because I tend to be pretty persistent in texting him or just walking over to the shop (next door to my office).

I’m getting the full aircraft ownership experience here for sure!

My plan of action is this: I want to get him to button everything up and run it. If it smooths out at all on the ground when running then I want to go ahead and go break that new cylinder in while at the same time get some good engine data.

Risks are obviously trying to fly with a brand new cylinder and one that isn’t showing good compression cold on the ground....

Thoughts from the group?

 

 

[Dialed In]

Where is the air escaping during the compression check on number three?  How did the cam and lifters look when the mechanic had the number one cylinder off?

[the_elkhartian]

Cam and lifters looked fine. He scoped and just looked with a mirror. 
 

His **theory** is that #3 is leaking at the exhaust valve where that carbon is built up unevenly. 

[carusoam]

Cleaning carbon out of the valve guides might be a good idea...

There is a process for that called the rope trick.

Carbon build up causes valves to stick...
 

It very much depends on how much carbon and where it is....

PP thoughts only, not a mechanic...

Best regards,

-a-

[Ragsf15e]

Interesting that it’s rough now... you didn’t say it was rough when you dropped it off there.  Why would a new cylinder make it rough?  It shouldn’t.  So all of a sudden this carbon buildup (which is probably legit) is making it rough when it wasn’t before?  I’m skeptical.

[jaylw314]

He's checking those compressions after the engine's warmed up, right?  checking compressions on a cold engine is pretty useless

[EricJ]

I think you're right to get some different eyes on it.   If I understand the problem correctly, staking the valve (basically whacking the valve stem) is specifically to shake loose uneven carbon deposits.   If the carbon is holding the valve open and causing the low compression, it should be easy to verify by hearing or feeling the air coming out of the exhaust manifold during a compression check.

I think your plan is a reasonable one.

[the_elkhartian]

Update....hopefully we're in the home stretch.

So mechanic wanted to go through and verify that all the lifters were working. Interestingly, he found a pushrod on the #3 cylinder with no part number and a different size hole on it from all of the other push rods (that had Lycoming P/N). He checked the valve clearance and found that the #3 was zero clearance and essentially just being held open. So, swapped in a correct pushrod and voila we had compression again on #3.

What doesn't make a lot of sense is why this happened all of a sudden, or just concurrently with the failure of the #1 valve seat? That incorrect pushrod has been in there (presumably) for years. Why did the valve stick open at this point?

He also found some other oddities....on some of the cylinders he noticed that there were two rocker shaft thrust washers used while the correct part for the engine is a single washer. (The two washers were pretty close, but not exactly the right thickness as the correct single washer.) He found that 2 lifters were different manufacturers than all the rest, and per Lycoming you can't mix & match lifters. So he cleaned those items up as well.

So, he's putting everything back together and we avoided pulling a second cylinder.

 

[carusoam]

WTW,

See if you can find when that cylinder was worked on in the past... Check the logs...

It may be possible that somebody went experimental while working on the cylinder...

As in they took parts that seem close... but aren’t the right ones...
 

See what else occurred under that owner’s watch... or That mechanic... or try to make sure there aren’t any other surprises like that...
 

We can invite Doc to have a look at the pics and see if he is familiar with the parts and their effects... 

Best regards,

-a-

[the_elkhartian]

She flies again! I got the airplane released earlier in the week. To summarize what was done:

• New (overhauled) #1 cylinder (nitrided, all the others are chrome)
• 2x new lifters to match all of the other lifters
• 4x new pushrods to update clearances and have approved part numbers
• Replaced all the valve rocker thrust washers because what was on there was all over the place
• Cleaned and flow checked the injectors
• Wallet sufficiently emptied/wife sufficiently disgusted

So I've been doing some break-in flights, just running it hard. I won't even start to brag about the TAS I'm getting at 25/25 down around 5500 feet

The new cylinder continues to run very cool on EGT compared to the others, however CHT is in line with everything else. The mechanic says that it could be a bad probe, or could be "normal" in comparison to the chrome cylinders. 

https://apps.savvyaviation.com/flights/4530281/af6ec16c-6b00-4961-a5a4-0313c6567ead

I'm planning to go do another flight tomorrow which will put me at about 7 hours since install. The engine shop breakin instructions say to change the oil after 5-10 hours and when oil consumption has stabilized. I run Phillips XC in the engine normally. For whatever reason the mechanic put Aeroshell 100 in....seems like he could have just kept the XC in there since it's a mineral oil, right? 

A few lingering thoughts:

1. It's been a tiring experience--mostly exhausting to have the airplane down for 6 weeks and not come out the other side with new gizmos or a fancy paint job...I'm basically back to square one.
2. Did the mechanic know what he was doing? Was some of this unneccessary exploratory surgery? Do I care at this point?
3. I have more insight and confidence in my engine now. Most pre-buys do not involve checking part numbers on the lifters & pushrods. But what is going to happen next?
4. How do you all buy off your wives when this sort of thing happens? It would be easier if my wife liked diamonds or furs, or fancy vacations....worse, she's super frugal and can't stand to spend money on anything!

 

[Ragsf15e]

3 hours ago, wingtipwalker said:

She flies again! I got the airplane released earlier in the week. To summarize what was done:

• New (overhauled) #1 cylinder (nitrided, all the others are chrome)
• 2x new lifters to match all of the other lifters
• 4x new pushrods to update clearances and have approved part numbers
• Replaced all the valve rocker thrust washers because what was on there was all over the place
• Cleaned and flow checked the injectors
• Wallet sufficiently emptied/wife sufficiently disgusted

So I've been doing some break-in flights, just running it hard. I won't even start to brag about the TAS I'm getting at 25/25 down around 5500 feet

The new cylinder continues to run very cool on EGT compared to the others, however CHT is in line with everything else. The mechanic says that it could be a bad probe, or could be "normal" in comparison to the chrome cylinders. 

https://apps.savvyaviation.com/flights/4530281/af6ec16c-6b00-4961-a5a4-0313c6567ead

I'm planning to go do another flight tomorrow which will put me at about 7 hours since install. The engine shop breakin instructions say to change the oil after 5-10 hours and when oil consumption has stabilized. I run Phillips XC in the engine normally. For whatever reason the mechanic put Aeroshell 100 in....seems like he could have just kept the XC in there since it's a mineral oil, right? 

A few lingering thoughts:

1. It's been a tiring experience--mostly exhausting to have the airplane down for 6 weeks and not come out the other side with new gizmos or a fancy paint job...I'm basically back to square one.
2. Did the mechanic know what he was doing? Was some of this unneccessary exploratory surgery? Do I care at this point?
3. I have more insight and confidence in my engine now. Most pre-buys do not involve checking part numbers on the lifters & pushrods. But what is going to happen next?
4. How do you all buy off your wives when this sort of thing happens? It would be easier if my wife liked diamonds or furs, or fancy vacations....worse, she's super frugal and can't stand to spend money on anything!

 

Most important thing first, find a good way to make the wife happy to support your flying habit!  My wife doesn’t like diamonds, furs, etc either, but she’s real happy going on a scenic flight to a new place for lunch in the Mooney!  Especially knowing it’s super safe with the new (better) cylinder!

The egt does look interesting, but cht is perfect.  Egt probe placement is pretty important to get a good reading.  Probably not critical, but have the mech take a look when you’re getting the oil changed?