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CHT 588, preignition?


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This is a question about my O-235 in a Cessna 152, so forgive me since it's not a mooney, but y'all are the best collection of technical aviation judgment and knowledge I've encountered:

tl:dr is that I think I had preignition, scoped the engine, mechanic wants to pull and likely replace the cylinder, and I want more opinions on the whole thing.

Here is the flight in question: https://apps.savvyaviation.com/flights/3452247/79782bde-5598-44e7-8306-2d461c601372.  Mag-check from 3-6 minutes, takeoff at 6 minutes, and at 9:40 I noticed CHT #3 was reading 588, so I pulled to idle and landed promptly.  

A runup on the ground showed the #3 bottom plug entirely non-functional (3:18 here), and so the mechanic gave me a new plug and his blessing to fly away.

Plug removed from #3.  Cracked Porcelain not visible here

IMG_2818.thumb.jpg.e407d139bd86f474c3e91255b0cfa9b0.jpg

However, a compression test ~2 flight hours later showed 60/80 with mist coming out of the oil fill cap, and the attached boroscope images.  Additionally, the valve cover was coated in something that looked like a bad egg dish. 

What say y'all about what happened (was it preignition, and if so what could have caused it?), and if there are any next steps beyond pulling the cylinder.

Valve:

IMG_6364.thumb.jpg.935578008210b393a8805a51de331c7c.jpg

IMG_2828.thumb.jpg.09d02a59019676e5e61fcbc42a937052.jpg

Piston:

IMG_6365.thumb.jpg.818e2975a018fa9270afb8750ab2cdf1.jpg

Valve Cover:

IMG_2812.thumb.jpg.3c85c3d0c191f00128edd0c154c4bb16.jpg

 

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Yes, broken porcelain on a plug could have caused that but I am a little surprised the EGT for that cylinder changed little during the apparent high CHT episode.  Any chance an exhaust gasket let loose and directed exhaust on the CHT probe?  The bad plug, iffy valve and lower compression may be unrelated.  Did the engine run rough while this was happening?  

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That cylinder needs repaired. The only way to get that stuff on only one valve cover is a really loose valve guide. The plug looks severely oil fouled. That along with the high temps could mean you have a broken ring. 

Either way you should pull the cylinder and have it repaired. There are still shops that will IRAN cylinders. Don’t forget the piston. 

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1 hour ago, MB65E said:

Did the oil redline too?

doubt it--i dont have it on the JPI, but since only one cylinder was hot, and only for ~2 minutes, i suspect the oil only cooked locally. The oil on the dip stick looks good, with no change from before. 

 

54 minutes ago, David Lloyd said:

Did the engine run rough while this was happening?  

Not at all, first and only indication was the high cht. mag check was perfect 3 minutes before the episode. 

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Just now, Browncbr1 said:

To me, that oil looks like water is in it..  do you unscrew your dip stick to vent moisture after each flight?

I don't, tbh with six guys sharing a plane, I suspect that's not likely to happen/I'd be too concerned that the next guy flying would forget to screw it back in. 

On the flip side, the airplane flies regularly on flights long enough to get the oil good and hot.

(And yes, there was quite a bit of condensation in that oil sludge, maybe 10ml total)

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Just now, tgardnerh said:

I don't, tbh with six guys sharing a plane, I suspect that's not likely to happen/I'd be too concerned that the next guy flying would forget to screw it back in. 

On the flip side, the airplane flies regularly on flights long enough to get the oil good and hot.

(And yes, there was quite a bit of condensation in that oil sludge, maybe 10ml total)

I recommend letting the dip stick vent for 5 or 10 minutes after each flight while you’re tying it down or whatever then screw it back in.  Water isn’t a lubricant, causes corrosion, and froths oil.     

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Just now, Browncbr1 said:

I recommend letting the dip stick vent for 5 or 10 minutes after each flight while you’re tying it down or whatever then screw it back in.  Water isn’t a lubricant, causes corrosion, and froths oil.     

Alright, I suppose I can do that at least--let some of the water out but also have the airplane squared away before the next person flies.

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Great problem solving technique, TG!

Pics and graphs and details are great...

Something stopped working at 9:00 minutes or so into the data collection...

Do all the plugs have the same lead balls stuck all over them?

This is a sign of low temps not burning off the lead...  

then the possibility of shorting the plug gap becomes more real...

If this plug failed, the EGT should rise for that cylinder...

Looking at the JPI graphs... EGT and CHT #3 are both showing the runaway...

The valve pic is showing the signs of not turning, and over heating... not the usual pizza pie image of a healthy valve...

High CHTs are a typical catalyst for pre-ignition...

Your JPI indicated how high the sensor got in a short period of time, the paint bubbling off the valve cover backs up what the JPI was saying....

While you are problem solving...

  • look to see what the other plugs look like... the lead balls stuck on the plug probably aren’t normal...
  • look to see what the other valves look like... the partial moon image is not normal...

There are a couple of tests for valve health and procedures for valve guide cleaning available...

You might want to send these details over to Savvy... to get a real opinion from a proper resource...

Mooney PP thoughts only, not a mechanic.

Best regards,

-a-

 

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@carusoam Thanks for the thoughts!  Since I'm not the only decision maker on this plane (downside of a six person partnership), longer-term members and the A&P have ended up driving the bus on this one.  At this point, the #3 cylinder has been pulled, the shop's IA says it shows no visible damage, the cylinder is going to a specialist to check it over and see if it's all in spec, and I suspect we'll reinstall, check the timing, and move on. 

Other plugs looked fine, and since the EGT only gets weird at 9:42 (when I pulled the power to idle), I suspect the plug is secondary to whatever caused the thermal runaway.  

I will probably see if the other 5 members can be sold on a Savvy maintenance subscription--if it turns out the cylinder didn't need to come off, that means the subscription would have paid for itself right there! (never mind the downtime and risk associated with it)

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Expect that the lead balls took more than one flight to develop...

if they are really lead balls...

The valve issue usually shows up in the Jpi graphs as a saw tooth pattern in the EGTs...

We have Paul that might be able to give some insight to what savvy can find in the data... 

 

with a cylinder failure like that the fingerprints won’t be hard to find... see how far they go back in history..:

learning to recognize the signs is better than having the failed cylinder in the climb out. I have that experience from an m20C...

 

with so many partners, the subscription probably makes easy sense/cents...

 

more PP thoughts only...

 

-a-

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50 minutes ago, carusoam said:

Expect that the lead balls took more than one flight to develop...

if they are really lead balls...

The valve issue usually shows up in the Jpi graphs as a saw tooth pattern in the EGTs...

We have Paul that might be able to give some insight to what savvy can find in the data... 

 

with a cylinder failure like that the fingerprints won’t be hard to find... see how far they go back in history..:

learning to recognize the signs is better than having the failed cylinder in the climb out. I have that experience from an m20C...

 

with so many partners, the subscription probably makes easy sense/cents...

 

more PP thoughts only...

 

-a-

I went back through since April, looking for anything amiss. It looks like there's plenty of hard use, but no classic saw-toothed pattern or anything else that looks bad to me. If you want to take a look, I'm curious what you think! 

https://apps.savvyaviation.com/my-flights/21121/f4f02577-b5be-4ff4-8061-0aeb82869d78

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Funny thing...

The link asks for a password and login data...

Any idea how to set that up without the login detail?

The list of flights is visible as is a high CHT alarm. But if I click on the data to open it it goes into the login mode...

Seeing if Paul is around... @kortopates

Best regards,

-a-

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1 hour ago, carusoam said:

Funny thing...

The link asks for a password and login data...

Any idea how to set that up without the login detail?

The list of flights is visible as is a high CHT alarm. But if I click on the data to open it it goes into the login mode...

Seeing if Paul is around... @kortopates

Best regards,

-a-

@tgardnerh The link you posted above is private, you'll need to bring a flight up and click on "Sharing Options" in the bottom right area of any flight, then specify if you want to share that flight only or all flights - that will give you a link you can use to share your data, but otherwise your data is private.

Edited by kortopates
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On 10/5/2019 at 5:01 PM, tgardnerh said:

This is a question about my O-235 in a Cessna 152, so forgive me since it's not a mooney, but y'all are the best collection of technical aviation judgment and knowledge I've encountered:

tl:dr is that I think I had preignition, scoped the engine, mechanic wants to pull and likely replace the cylinder, and I want more opinions on the whole thing.

Here is the flight in question: https://apps.savvyaviation.com/flights/3452247/79782bde-5598-44e7-8306-2d461c601372.  Mag-check from 3-6 minutes, takeoff at 6 minutes, and at 9:40 I noticed CHT #3 was reading 588, so I pulled to idle and landed promptly.  

A runup on the ground showed the #3 bottom plug entirely non-functional (3:18 here), and so the mechanic gave me a new plug and his blessing to fly away.

Plug removed from #3.  Cracked Porcelain not visible here

IMG_2818.thumb.jpg.e407d139bd86f474c3e91255b0cfa9b0.jpg

However, a compression test ~2 flight hours later showed 60/80 with mist coming out of the oil fill cap, and the attached boroscope images.  Additionally, the valve cover was coated in something that looked like a bad egg dish. 

What say y'all about what happened (was it preignition, and if so what could have caused it?), and if there are any next steps beyond pulling the cylinder.

Valve:

IMG_6364.thumb.jpg.935578008210b393a8805a51de331c7c.jpg

IMG_2828.thumb.jpg.09d02a59019676e5e61fcbc42a937052.jpg

Piston:

IMG_6365.thumb.jpg.818e2975a018fa9270afb8750ab2cdf1.jpg

Valve Cover:

IMG_2812.thumb.jpg.3c85c3d0c191f00128edd0c154c4bb16.jpg

 

Based on the  posted monitor data, this pre-ignition event leading to runaway CHT is horrifyingly real. Good for you for spotting it quickly and saving yourself!  Please dump that jug in the trash now and put on a new one!!

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2 minutes ago, kortopates said:

@tgardnerh The link you posted above is private, you'll need to bring a flight up and click on "Sharing Options" in the bottom right area of any flight, then specify if you want to share that flight only or all flights - that will give you a link you can use to share your data, but otherwise your data is private.

Had no trouble pulling up on my iPad....scary3D92C439-7A4B-4EC5-B39A-306418EE6EFB.thumb.png.5d25742d795f9706040111cd722b203b.png

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6 minutes ago, DXB said:

Had no trouble pulling up on my iPad....scary3D92C439-7A4B-4EC5-B39A-306418EE6EFB.thumb.png.5d25742d795f9706040111cd722b203b.png

@DXB you have me worried, Please let us know @tgardnerh if you did use the sharing option to get that link? 

We just rolled out  new system last week and still correcting a lot of bugs. Investigating further, the link that is posted is of the type we use for sharing all flights - however when I looked at his data, it is labeled "Private" to me me, which is why I responded like I did. I did a test on another N number and it looked to work correctly, but I'll pass this on as a potential issue to our web guy to investigate further.  

But it would be helpful to confirm tgardnerh did clickon the sharing option to get that link as I suspect?

 

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Many are expecting the cylinder to be heading for the scrap pile...

With pre-ignition, the piston crown may be showing some issues as well...
the act of pre-ignition has a tendency to disrupt the boundary layer that protects the piston from the high heat of ignition...

So... be on the look-out for signs of pre-ignition... possibly melted parts, edges, or center, of the piston crown...

Since this only happened to one cylinder... be on the look out for places where glowing embers May have caused the early ignition...

that really dirty plug has a lot of things that could qualify as a glowing ember...

then try and figure out what caused that plug to be so cruddy.

PP thoughts only, not a mechanic...

Best regards,

-a-

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3 hours ago, carusoam said:

Dev,

That’s the first link... and it worked well...

The next link with several flights is all locked up.

Fortunately Paul has given us the key of why that happens...

now we wait for tg to get back... :)

Best regards,

-a-

The all flights link was a bug, and it should be now fixed for you Anthony, try it again when you can.

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Paul,

The link is now working as expected!

(the power of MS at work... :))

One thing you can share with your tech team...

In general, not this particular case, some shared graphs are a challenge to read...  it is hard to know if the X axis, time, is seconds, minutes, or days... labels would be helpful... just to clear up/confirm what I am seeing compared to what a user has posted...

 

In this case, the data seems to be so coarse, the data collection rate seems to be a few points per minute...?

the sawtooth pattern we are looking for, may have gotten lost due to the JPI setting for data collection..?

a great sales tool for Savvy.... would be to find/show this bad valve’s foot prints in the existing data... (if that is possible)

The way this engine monitor was set-up, it alarmed as CHTs exceeded 400°F on every flight... and got ignored each time... on the ‘accident’ flight... the real hot CHT probably didn’t stand out from the noise of every other flight... 

There is definitely room for a service from Savvy... getting a customer’s JPI set up properly... data point collection rate, and alarm/warning settings...

PP thoughts only, not a mechanic or data analyst...

Best regards,

-a-

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