EGT Analysis

[Mike A]

I have been analyzing the data from my newly installed JPI 730 and noticed that towards the end of a flight from PDK to ORL the EGTs on cylinder 2 have begun to look like a sawblade.  It can jump or drop 100dF in a matter of seconds.  I'm afraid this means that I have a sticking exhaust valve.  Does anyone else have any suggestions to why it is doing this?  This did not appear until last week.

 

Here is a link for a shorter flight that where it is doing the same so you can see what I'm talking about:

 

https://www.savvyanalysis.com/flight/487165/3ee05526-c621-4950-b2ec-e39ee45c4002

 

and the original flight where it started:

https://www.savvyanalysis.com/flight/484105/a3b979b9-e24b-4b91-a889-a8e6e55d7520

 

What do yall think?

 

 

[orionflt]

probably a loose connection, had the same thing on mine, re crimped the connector and secured the wire and it was nice and steady again

[Bob - S50]

Notice how the sawtooth is cyclical and regular?  If you'll watch Mike Busch's webinar or read this article of his:

 

http://www.sportaviationonline.org/sportaviation/201008#pg109

 

I think you may have an exhaust valve that is about to fail.  If I were you I would not fly the airplane until I have a good mechanic borescope that cylinder and take a close look at the exhaust valve.  I'll bet you have an asymmetric pattern on the valve face as mentioned in the article.

 

Good luck,

 

Bob

[jlunseth]

It could be either one.  I definitely agree with the recommendation to have the engine checked out, but would have the mechanic start with the connection.  What is a little suspicious to me is the size of the fluctuation.  I have seen the same pattern from bad connections to the probe, but not that large in terms of temps. 

 

One thing to have your mechanic check is not just the tightness of the connection, but the order in which things are installed.  There is a very specific order in which the parts go together on the probe, including a couple of small star washers, I don't remember the order but it is not uncommon for A&P's to install them incorrectly.  You can get the order from JPI or from the install manual.

[orionflt]

I won't discount the possibility of a connection problem, but Bob may be correct, I didn't take a look at the graph when i made my first post but looking at it and the consistency of the peaks it does look like you should take a look at the exhaust valve.

[Mike A]

It is on the docket for inspection Thursday.

 

Assuming the worst, what should I expect to pay for replacing the valve or does that mean the whole jug needs to be replaced?

[carusoam]

Am I seeing the right graph?

(1) there is a 6 cyl engine on a long flight(over 1 hr)

(2) CHT spreads are from 270 to 360. That's pretty large? (why is that?)

(3) at or near shutdown, two CHTs increase while the others are cooling...(what causes that?)

(4) the sawtooth EGT is odd, at/near shutdown it drops off unlike the others... (what causes that?)

On my 6 cylinder, all EGTs and CHTs trend similarly and are closer together. I have one notable warm cylinder #5, which resides behind the generator....

Seems like there are too many things going awry, or at least need answers to.

Do you have any older graphs that show all six behaving similarly?

On the other hand, I may be looking at the wrong graph....

Best regards,

-a-

[Mike A]

Am I seeing the right graph?

(1) there is a 6 cyl engine on a long flight(over 1 hr)

(2) CHT spreads are from 270 to 360. That's pretty large? (why is that?)

(3) at or near shutdown, two CHTs increase while the others are cooling...(what causes that?)

(4) the sawtooth EGT is odd, at/near shutdown it drops off unlike the others... (what causes that?)

On my 6 cylinder, all EGTs and CHTs trend similarly and are closer together. I have one notable warm cylinder #5, which resides behind the generator....

Seems like there are too many things going awry, or at least need answers to.

Do you have any older graphs that show all six behaving similarly?

On the other hand, I may be looking at the wrong graph....

Best regards,

-a-

 

 

1) That is correct.  There are two graphs - one for a 2.5 hr flight and one for a 1 hr flight

2) The low CHTs in flight are are the front two that get the most airflow.  They always report well below the others which are nicely grouped.  Cylinder 3 used to climb a bit, but i fixed a baffeling problem and that doesn't seem to be an issue anymore

3) Checkout my previous post titled Low EGT at Idle and Low FF at Full Power - the 2 CHTs that dive are in the back, which also have a sharp dropoff of EGTs.  Responses to the previous posts attribute that to poor air distribution when the turbo is at idle

4) I got nothing on this one

 

The 730 has only been in it for 2 weeks or so, so I have no other data. The only difference in any of the flights (which is about 12 hrs worth) is the appearance of the sawtooth pattern.

[carusoam]

Do you have the turbo (TIT, CDT) wired to the 730 as well?

Bring your graphs and questions to your mechanic.

Best regards,

-a-

[Marauder]

It is on the docket for inspection Thursday.

 

Assuming the worst, what should I expect to pay for replacing the valve or does that mean the whole jug needs to be replaced?

 

I read the article Bob provided and it sure looks like an exhaust valve problem. The article says to have it borescoped to see if the valve is showing hot spots or wear before pulling the cylinder. By any chance, have you been doing oil analysis as well? The articles says that an increase in nickel is another leading indicator.

 

The article continues on and says that if it is caught early enough, the valve and guide are just replaced. If the valve breaks, it is a different story.

 

Bob -- thanks for sharing the article. Very informative.

[jlunseth]

Here is the info. I got from John Deakin on the installation of probes and the order of the washers.  In my case, it was the CHT that was "jagged."  I should hasten to say that one of the things they taught at the course, was that a jagged EGT may be a stuck valve.  At any rate, here is what he said about installation of the probes: "Check to be sure the tiny "star washers" are in between the connectors, instead of the more common location under the tiny nut.  They usually serve as lock-washers, except in this case."

[kmyfm20s]

IIRC it is from a burnt valve not a stuck valve that you see the cyclical nature of the EGT rise. Everytime the valve is opened and closed it rotates slighty. At a certain point in the rotation it lets more gas escape showing the high EGT. Is this the first flight that it has happened?  It could just be some carbon or lead stuck on the valve. Borescoping the valve is your best bet!

[N201MKTurbo]

A intermittently fowling spark plug or a intermittent mag would do the same thing. You can normally feel that as a slight shudder as the spark plug goes on and off. Have you tried a mag check while the EGT is high?

[N201MKTurbo]

OK, I just looked at your charts, I can't imagine a spark plug or mag being that regular. I have to go with the crowd.

[Mike A]

The shop ran a compression test on the cylinder that was fluctuating and it came out at 71/80, however when they had it on pressure there was significant noise and noticeable air moving out of the oil fill tube and some out the exhaust.  I assume that the exhaust leak is from the dying/corrupted exhaust valve, but they were also concerned about blow-by of the piston rings which was causing the air to escape into the oil sump and out the fill tube.  They want to pull the cylinder and potentially send it off to be honed and have the ring replaced.

 

All the even numbered cylinders presented air-flow noise in the oil sump, but the #2 cylinder is the only one where you could physically feel air moving out of the fill tube.  Also, we checked each of the cylinders and all the compressions were 70+/80 (with a few as high as 78).  This engine has +/- 600 hrs since re-man.  I am slightly concerned because they seemed to turn their attention to this rather than the exhaust valve, which was the reason I brought it in in the first place but this seems to be the bigger money-maker for them.  

 

Any advise from our fellow A&Ps is more than welcome.

[DonMuncy]

Borescope it and report back.

[KSMooniac]

Definitely borescope the suspect cylinder before removing it.  I suspect you'll need to get the exhaust valve reworked at a minimum, but the borescopes are cheap enough now that every mechanic should have one.  You can tell by the deposit/heat patterns on the valve face if it is sealing evenly or not.

[Guest]

You should read TCM s/b 03-3 cylinder compression testing and TCM s/b 89-9 crankcase pressure checks. If ring blow by is too high the crankcase pressure will be higher than 4.0" H2O or 90 mph on an airspeed indicator. You'll likely find that your rings and cylinder walls are fine and your valve is the problem.

Clarence

[M20S Driver]

The shop ran a compression test on the cylinder that was fluctuating and it came out at 71/80, however when they had it on pressure there was significant noise and noticeable air moving out of the oil fill tube and some out the exhaust.  I assume that the exhaust leak is from the dying/corrupted exhaust valve, but they were also concerned about blow-by of the piston rings which was causing the air to escape into the oil sump and out the fill tube.  They want to pull the cylinder and potentially send it off to be honed and have the ring replaced.

 

All the even numbered cylinders presented air-flow noise in the oil sump, but the #2 cylinder is the only one where you could physically feel air moving out of the fill tube.  Also, we checked each of the cylinders and all the compressions were 70+/80 (with a few as high as 78).  This engine has +/- 600 hrs since re-man.  I am slightly concerned because they seemed to turn their attention to this rather than the exhaust valve, which was the reason I brought it in in the first place but this seems to be the bigger money-maker for them.  

 

Any advise from our fellow A&Ps is more than welcome.

Is your mechanic using the right orifice at 80 psi? My guess is that he is using a larger orifice than recommended by continental.

Masoud

Not an A&P

[Bob - S50]

The shop ran a compression test on the cylinder that was fluctuating and it came out at 71/80, however when they had it on pressure there was significant noise and noticeable air moving out of the oil fill tube and some out the exhaust.  I assume that the exhaust leak is from the dying/corrupted exhaust valve, but they were also concerned about blow-by of the piston rings which was causing the air to escape into the oil sump and out the fill tube.  They want to pull the cylinder and potentially send it off to be honed and have the ring replaced.

 

All the even numbered cylinders presented air-flow noise in the oil sump, but the #2 cylinder is the only one where you could physically feel air moving out of the fill tube.  Also, we checked each of the cylinders and all the compressions were 70+/80 (with a few as high as 78).  This engine has +/- 600 hrs since re-man.  I am slightly concerned because they seemed to turn their attention to this rather than the exhaust valve, which was the reason I brought it in in the first place but this seems to be the bigger money-maker for them.  

 

Any advise from our fellow A&Ps is more than welcome.

I think your A&P just wasted some of your money.

 

From what I've read, compression checks are pretty much useless.  They do them as part of an annual because they are required to, essentially "because that's the way we've always done it."  Many years ago it was the best they had.  Now they have much better options.

 

IMO they should have done a borescope to look at the valve in the first place.  While they were in there, they could look at the cylinder walls too.  Much more informative.  Now you've paid for his time to do a compression check and will end up paying for his time to do a borescope.  If they find the valve is bad, while they have the top off and the equipment there, I would personally have them borescope all the other cylinders too.  Why get one cylinder fixed and then 6 months later have another one go bad.  It may be you only find one bad cylinder or you might find a couple.  If the plane is going to be down for several weeks/months, might as well get all the bad ones fixed and not have to worry about it for a few years.  But don't fix good ones.

 

If the valve is bad, they will have to pull the cylinder to have it worked anyway.  Doesn't matter if they are pulling the cylinder for honing or the valve, it has to come off to work on either.  The question is though, how do you know the cylinder walls are bad enough to need pulling?  The compression test alone would say no.  As mentioned above, the amount of blow by would be more definitive.

 

I wouldn't bother paying the A&P to do a blow by check until he does a borescope.  If the valve is bad, why waste the time and money to pay for a blow by check?

 

Good luck,

 

Bob

[orionflt]

I do not disagree with doing a compression check, that can tell you a lot about what is going on with your cylinder, but it won't tell you everything, borescope it before you have it pulled off. you may need to pull the cylinder anyway but know the full story before doing any major surgery. it could be a burnt valve or something as simple as a piece of carbon keeping the valve from seating properly, I have also seen worn guides that allow the valve to float and not seat properly. any of the last 2 discrepancies can be repaired with out removing the cylinder. the bore scope will also tell you if there is scoring on the cylinder walls or improper wear causing blow by into the crank case. continentals are notorious for lower compressions, that is why they have a complete procedure that tells you whether your cylinder is still airworthy even if you have a low compression during the test. your compressions were still in the 70's so you can not be getting very much blow by past the rings especially if you getting exhaust leakage also. 

 

Brian

[jlunseth]

Compression tests for TCM engines are often done incorrectly.  Here is the link to the TCM Service Bulletin that specifies how the check must be done.  http://www.tcmlink.com/pdf2/SB03-3.pdf

 

I am not an A&P so take what I say with a grain of salt, but as it has been explained to me, the standard test looks at max. pressure that can be generated in the cylinder briefly, and the TCM test is more of a measure of how much pressure the cylinder can hold for a period of time.  It is not at all uncommon to see pressures down as low as 45, in perfectly good cylinders, using the TCM test.  It is not inconceivable that pressures might be in the 70's either, but much less likely if the correct test is done.  SB303-3 also discusses what to look for to determine if a valve is leaking.

[chrisk]

Hey Mike,

I know it has only been two days, but any updates on what you have found would be appreciated.  I'm crossing my fingers that it is something minor.

[Mike A]

So amazingly the shop on my field didn't ever get the equipment to inspect the valve, but annual time came and my more trusted mechanic and I checked the compression, which was at zero and blowing through the exhaust pipe. This ended the annual for the time being. He wanted to get a few lingering projects done before we attacked the cylinder, so we are going to pull it next weekend, hopefully. I'll post pics of everything we find.