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CHT 588, preignition?


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Interesting observations...

The runaway CHT (15:43) is not the last flight of the day.
The plane made another flight after that one..? (17:33) :blink:

Interesting flight.... (10/2,14:08) many T/Os in repetition... EGT1&2 are on a different track than 3&4.  This is consistent in all the flights... sub-optimal fuel distribution..?

The run-ups on each flight are occurring so quickly, the data points are so few, the valuable data review seems non-existent...

There is an inflight mag check... this seems to show just a bit more detail... more data, less noise... (worth a closer look)

Surprise..?  left and right are showing different responses... one mag may be weaker than the other or the dirty plug might be showing up here..? (Look at the last flight, 23 minutes in, two small peaks in cruise, expand the view... see the difference)

 

One thing that adds to the challenge for me... this is not a Mooney engine with Mooney baffles... the EGT distribution is a bit odd from what we are normally seeing on MS...

What stands out... If your work plane has an engine monitor on it...

  • get it set-up to collect the most data possible.
  • slow the run-up process down a hair to collect a few more data points, don’t rush through the steps...
  • set the alarms to be meaningful... not to get ignored.
  • fly a standard data collecting flight to really clean up the data, and minimize the noise... typical of the flight profiles detailed on Savvy’s site...

Still only a PP, not a combustion expert... or data engineer, or engine monitor guru...

Best regards,

-a-

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4 hours ago, carusoam said:

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...

 - The shared graph is displayed identically as any graph, these are time series graphs with time on the X axis in format of hours:min:sec. I believe that's covered in our instructions or help text that I no longer see on my interface, but hopefully you still a Help or user guide link.

 

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

- in this case the monitor is recording at a 6 sec interval, which is the default for this legacy monitor (EDM-730) and provides very poor data resolution. I advise all our clients to use the fastest data sampling rate supported by their monitor upto 1 sec rate (this one supports a 2 sec rate).

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

- an issue with a 6 sec sampling rate

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)

- our automated s/w at the time of data upload checks the data for a FEVA signature and if found notifies an analyst to review. If the analyst agrees, the owner is then notified by our analyst for follow up. 

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... 

- True, the owner sets up an aircraft profile specifying at what CHT temp they want to use as a threshold, in case 400F

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...

- Indeed, something each analyst does with each of our Pro clients, but of course this is free account that we have no interaction with.

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

Best regards,

-a-

Anthony - responses in green text above

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6 minutes ago, tgardnerh said:

I thought that's exactly what I'd done!  Try this one: https://apps.savvyaviation.com/my-flights/21121/f4f02577-b5be-4ff4-8061-0aeb82869d78

Indeed, the "my-flights" is a shared flights, I got thrown off because your flight still showed "private". And we did have a sharing bug that Anthony alerted me too which got fixed last night. Plus I didn't notice at first you had posted 2 different links, one for all flights liek the one above and one for just the high CHT flight.

2 minutes ago, tgardnerh said:

 

That's exactly how I generated the link!

Thanks for confirming! Due to the bug, I wasn't quite sure. But when I realized it was a "my-flights" link I realized that's the only way to get it - via the sharing option.

Edited by kortopates
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8 hours ago, carusoam said:

data collection rate seems to be a few points per minute...?

The incident flight is on a 6 second interval, so 10/minute.  

8 hours ago, carusoam said:

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... 

On the actual monitor the alarm is set at 450--it was the bright red flashing light that got me to pull the power to idle! 

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TG,

did you see my notes on the speed of the mag checks and the inflight mag check?

If you were to wait for a few data points to be collected... at one per six seconds... it takes 18 seconds on each position...

See if you can set to a faster collection rate... 2 seconds can usually be selected... the newer more capable JPIs can achieve 1 data point every second... still kind of slow in the data handling world...

What I did see was in the last flight... the two mag checks were not identical like they usually should be... indicating one mag and it’s related plugs is not behaving as well as the other...

All plugs normally behave in near identical ways... so the EGTs should All peak in the same place for all eight plugs...

the first mag check looked ‘normal’ the second mag check had an array of peak EGTs that we’re different...

 

If you can... do some extended run-ups on the ground to see if you can collect enough data points to demonstrate what is really happening...

Some people avoid extended run-ups for various reasons... save time, keep things from heating, avoid drawing dirt into the prop...

in this case, it is worth slowing things down to collect better data...

See if you can get the data collection up to the 2 sec speed...

The speed of things happening is quite slow EGTs are not on/off it takes a few moments to reach their new peaks... you can see this happening on the instrument as you switch the key... let them peak... let them come back down... let them peak again on the other mag... let them come back down...

You will see one or two things happen...

1) the mags are equally timed, and the plugs are working well... the peaks will be mirror images of each other all the EGTs will have the same peak....

2) One mag is weak, the plugs don’t work as well... the peaks will not be the same...

As far as that ugly plug goes... there are a couple of reasons for failed plugs... are you familiar with checking the resistance of plugs? Over the last few years Champion has demonstrated difficulty in maintaining manufacturing quality... the plugs that are supposed to be low resistance... have a tendency of running into high resistance over time... high resistance causes weak ignition...

there is no need to fly this plane with the valve showing that is not operating properly... and the chance of the thermal runaway repeating itself is just too great... or the valve sticking either closed or open will be bad...

I had a valve stick open... it crashed into the top of the piston and left a mark and bent the valve stem...

PP thoughts only, I am not a mechanic...

Best regards,

-a-

 

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@carusoam, I did see those notes, though the time for conservative management has past (in the sense that the cylinder is currently sitting on a workbench, which sort of precludes the "gather more info first" strategy).

As of now, the #3 cylinder is either getting OH'd or replaced. The plan is to also check the other 3 cylinder head covers for the oil sludge we found on #3, and check all 4 compressions, and check the timing (spark plugs have already been checked for fouling).

Once the airplane is whole again, I'll set the JPI to record on a 2 second interval (quickest possible), and upload proper Savvy profile recordings for the first flight, and another flight once the cylinder is broken in. If the mag checks then look off, I'll check plug resistance.

Is there anything else you'd do in my shoes?

 

To everybody who has chimed in, thank you! The collective response here has been incredibly helpful. This is a side of aviation that PPL training just doesn't cover, and I couldn't ask for a better crowd to help out with the "Oh shit, now what?" questions.

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Just now, tgardnerh said:

Is there anything else you'd do in my shoes?

 

Go Mooney! :)

 

If / when your cylinder work works out...

Through history....

On average, everyone gets to experience an engine out in their flying lifetime...

This is as close as you can get to have all the experience without having the engine out...

I had the stuck valve... that is a pretty strong reminder that using the engine monitor effectively can be a great way to avoid your share of engine outedness(?)

My O360 didn’t have an engine monitor...

Thanks for putting in all the effort to collect and share your data!

Start reading up on the break-in procedure for a new or OH’d cylinder... advise your partners properly...

PP thoughts only, not a mechanic...

Best regards,

-a-

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  • 1 month later...

To close this out:

The cylinder came off, and the verdict was that the valve guides and valves were bad, the cylinder barrel was polished smooth, and the piston was scored on the sides (presumably from contacting the cylinder, and also badly pitted (I presume whatever was going on in there eroded that aluminum pretty fast).

Since then, I also had an event that has been tentatively diagnosed as a stuck carb float, but manifested as partial power loss over mountains. I put the airplane down on the nearest airfield, and found blue staining all over the nose-wheel.  

All this, combined with the fact that every new mechanic who looks under the cowling says something to the effect of "ehh, i guess it's airworthy," means that if anybody is in the market for a 1/6th share of a Cessna 152 based at KSQL,  I've got one for sale.

Thank you everybody for helping me navigate this adventure!

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Piston pitting is indicative of preignition.  This is also manifested in CHT rising 2-3 degrees a second.  There have been a few Incidents documented by Mike bush. One was a Bonanza with a bad plug that caused preignirion.  CHT off the scale and then a holed piston.  The other was a cirrus.  Mag problem it was firing way too early.  Both trashed a complete engine. 

Edited by jetdriven
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4 minutes ago, jetdriven said:

Both trashed a complete engine. 

I think I watched that webinar maybe 3 weeks before this incident.  When I saw the crazy-high CHT I more or less heard Mike Busch on my shoulder telling me "pull the power to idle NOW."  Probably saved the engine, and maybe even avoided a serious accident.

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TG...

You have too much to lose, not enough to gain...

It is not normal to have six people have the problems you are seeing...

1) The cylinder was failing, and somebody took the plane flying again...

2) The carb poured gasoline all over the engine compartment... this is a major fire risk!

3) JPI data was showing things that could be improved upon.

4) Spark plug so dirty it couldn’t operate properly...

5) this is similar to Russian roulette, aviation style... you have a 1:6 odds that the next failure will happen while you are PIC...

6) get the money together to get the maintenance done that is required...

7) ‘I guess it is airworthy’ is not the response you want...

8) Find a mechanic that can show you it being airworthy...

9) carb, mag, engine OHs are all low cost when divided by six...

10) A single funeral costs way more than the maintenance that is being asked for by this plane...

The plane is screaming to you...

Run, don’t walk...

Private Pilot thoughts regarding the details given above... not a mechanic.

This is not normal for any plane... the fuel system needs help.  The ignition system needs help. A cylinder failed miserably. The carb tried to light the plane on fire at altitude over mountains...

it is OK to walk away while you are still alive.

How many hours are on this engine?  It sounds like it was completely worn out already...

how does it look to you?

Best regards,

-a-

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