IO-550A Hot Cylinder Troubleshooting

[Ryan121b]

Hey all, I have an M20J Missile with an IO-550A. After a prop strike inspection early this year and annual, the #4 CHT is excessively high on initial climbout now that I'm at my home field (NW LA). I'm hoping someone might be able to point out a potential area I may have missed. I'm having a hell of a time finding an A&P to help, so I'm hoping to have the issue narrowed down before they show up.

CHT #4 reached 490F briefly during takeoff on an 85F day, once airspeed increased, temps reduced below 440F, but still not where I need them to be.

• CHT gasket probes are installed on the lower spark plugs on all cylinders. CHT probes were swapped around and ultimately replaced, they are valid readings and still high CHT on #4
• Flexible baffle seals will be replaced: they are split / deformed in various areas, but I can't believe this alone would be the root cause of such a high CHT spike on just the #4 cylinder
• Rigid baffle seals appear normal
• GAMI injector nozzles: checked / visually verified clear. I'm considering whether the nozzle may need to be adjusted by GAMI, but I can't get an in-flight test until I mitigate the high CHT before my next takeoff.
• Fuel line 'bottle test' (without injectors attached on the lines). #4 was the highest by a small amount, I believe issues would arise if it were excessively more lean than the others
  • #1 cyl - 3.15 fl oz
  • #2 cyl - 2.95 fl oz
  • #3 cyl - 3.45 fl oz
  • #4 cyl - 3.50 fl oz*
  • #5 cyl - 3.20 fl oz
  • #6 cyl - 3.20 fl oz
• Cylinder borescope showed nothing significant / concerning
• EDIT: Spark plugs were checked and reinstalled

If anyone has any insights or potential areas to target, it would be greatly appreciated. I'm hopeful the flexible baffle seals will help, then thinking of having GAMI modify the #4 injector.. other than that, I'm a little stuck.

Edited December 7, 2023 by Ryan121b
added info

[Shadrach]

You either have insufficient cooling airflow, excessive internal cylinder pressure (mixture,timing, etc) or both. 

It looks as though that, for the most part, you’ve eliminated fuel delivery as a potential problem.

If this we’re a timing issue, the problem would very likely manifest across all cylinders.

So an airflow issue seems most likely.
In rare cases, exhaust leaks can blast a cht probe and cause false readings.

Are all other CHTs in the normal range? 

Are you able to upload engine monitor data? 

Have you thoroughly examined the internal cylinder baffles? 

 

 

 

[Ryan121b]

1 hour ago, Shadrach said:

You either have insufficient cooling airflow, excessive internal cylinder pressure ( mixture,timing, etc) or both. 

It looks as though that, for the most part, you’ve eliminated fuel delivery as a potential problem.

If this we’re a timing issue, the problem would very likely manifest across all cylinders.

So an airflow issue seems most likely.
In rare cases, exhaust leaks can blast a cht probe and cause false readings.

Are all other CHTs in the normal range? 

Are you able to upload engine monitor data? 

Have you thoroughly examined the internal cylinder baffles?

https://apps.savvyaviation.com/flights/shared/flight/7405304/b463ddf0-9c5c-4698-970d-be99e497cd5d

https://apps.savvyaviation.com/flights/shared/flight/7186313/e0c92d2e-9c62-4961-8b9c-0ad0c6e12f7b

Here is the engine monitor data from the previous two flights. I had the engine borescoped after the first flight, and had the total fuel flow increased to help reduce temps during takeoff, but still had high CHT.

The other CHTs appear normal, I haven't closely examined the internal baffles. The timing has been verified twice to be within limits, although an exhaust leak would hopefully be an explanation for the CHT readings. I debated swapping the CHT probe to the top spark plug position to see if that would cause a big difference.

[1980Mooney]

1 hour ago, Ryan121b said:

https://apps.savvyaviation.com/flights/shared/flight/7405304/b463ddf0-9c5c-4698-970d-be99e497cd5d

https://apps.savvyaviation.com/flights/shared/flight/7186313/e0c92d2e-9c62-4961-8b9c-0ad0c6e12f7b

Here is the engine monitor data from the previous two flights. I had the engine borescoped after the first flight, and had the total fuel flow increased to help reduce temps during takeoff, but still had high CHT.

The other CHTs appear normal, I haven't closely examined the internal baffles. The timing has been verified twice to be within limits, although an exhaust leak would hopefully be an explanation for the CHT readings. I debated swapping the CHT probe to the top spark plug position to see if that would cause a big difference.

Rather than swap the probe position on #4, can you swap the probe to an adjacent cylinder in order to prove that your readings are accurate and not caused by a faulty probe?

Second, since the IO-550A is unique to the Missile, I assume that your mechanic took pictures of all the baffling, cabling, hoses, etc before removing/tearing down your engine for the internal inspection.  Do you have those pics to compare with your current baffling?

 

[Shadrach]

2 hours ago, Ryan121b said:

https://apps.savvyaviation.com/flights/shared/flight/7405304/b463ddf0-9c5c-4698-970d-be99e497cd5d

https://apps.savvyaviation.com/flights/shared/flight/7186313/e0c92d2e-9c62-4961-8b9c-0ad0c6e12f7b

Here is the engine monitor data from the previous two flights. I had the engine borescoped after the first flight, and had the total fuel flow increased to help reduce temps during takeoff, but still had high CHT.

The other CHTs appear normal, I haven't closely examined the internal baffles. The timing has been verified twice to be within limits, although an exhaust leak would hopefully be an explanation for the CHT readings. I debated swapping the CHT probe to the top spark plug position to see if that would cause a big difference.

All of your CHTs look elevated to me. What is take off fuel flow? Looking at your July flight, your full rich max power EGTs are 100-150° Higher than mine. Things look better in September, but more fuel would likely help. I suspect there is an issue with baffle install. 
 

Do you have any pre prop strike data?

[Ryan121b]

37 minutes ago, Shadrach said:

All of your CHTs look elevated to me. What is take off fuel flow? Looking at your July flight, your full rich max power EGTs are 100-150° Higher than mine. Things look better in September, but more fuel would likely help. I suspect there is an issue with baffle install. 
 

Do you have any pre prop strike data?

Thanks for taking a look, takeoff fuel flow is now set to 27 gph for takeoff, I've read that other folks have set it higher though.

I am looking into the baffle install photos from the teardown, it was off-station so I wasn't present during the process, I'm reaching out to the mechanic now.

pre prop strike flight: https://apps.savvyaviation.com/flights/shared/flight/7133120/a36ca306-f2c9-48e4-bb61-cde5ac113fff

[Ryan121b]

1 hour ago, 1980Mooney said:

Rather than swap the probe position on #4, can you swap the probe to an adjacent cylinder in order to prove that your readings are accurate and not caused by a faulty probe?

Second, since the IO-550A is unique to the Missile, I assume that your mechanic took pictures of all the baffling, cabling, hoses, etc before removing/tearing down your engine for the internal inspection.  Do you have those pics to compare with your current baffling?

 

Initially I swapped the probes between #2 and #4 cylinders as #2 was the coldest on the left side. They indicated that #4 cylinder (read by the #2 probe on the #4 cylinder) was still higher than the others. Afterwards I did have the #4 CHT probe replaced with a new gasket probe, since it had some fraying, but the temperatures remained consistently high on that cylinder.

And that's a great point on the baffle photos, I've reached out to the mechanic for photos they may have.

[Fly Boomer]

20 minutes ago, Ryan121b said:

takeoff fuel flow is now set to 27 gph for takeoff

I don't have a 550, but that sounds dangerously low to me.  I would expect something in the 30s.  Maybe even mid-30s.  On my TSIO-520, Rocket calls for 33 GPH on takeoff, and some guys set them up to 34 or 35 for takeoff fuel flow to keep temperatures under control.

[Ryan121b]

These photos are current day, the last photo is pre-strike inspection condition. Admittedly I knew little of the flexible baffle seals until recent troubleshooting, I'm concerned with the holes / wear from punctures on the left side of the engine, as well as the mis-formed section at the left rear of cylinder #2. On the back right side, the flexible seal is sliced, which seems like it was done to allow the seal to bend but also seems like it would allow far too much air through the back via all the gaps.

Pre-strike-inspection condition:

[Fly Boomer]

3 minutes ago, Ryan121b said:

On the back right side, the flexible seal is sliced, which seems like it was done to allow the seal to bend but also seems like it would allow far too much air through the back via all the gaps.

I'm not smart enough to know if those baffle seals are okay, but keep in mind that they will look different when pushed down and together by the cowling.

[Shadrach]

44 minutes ago, Ryan121b said:

Thanks for taking a look, takeoff fuel flow is now set to 27 gph for takeoff, I've read that other folks have set it higher though.

I am looking into the baffle install photos from the teardown, it was off-station so I wasn't present during the process, I'm reaching out to the mechanic now.

pre prop strike flight: https://apps.savvyaviation.com/flights/shared/flight/7133120/a36ca306-f2c9-48e4-bb61-cde5ac113fff

Even your pre prop strike numbers were on the hot side. You need 29.5gph for take off. Start there.

[Bolter]

@Ryan121b Is this still break-in operation time after the rebuild/post-strike inspection?  Cylinders will run hot when overhauled or new.  If they honed the cylinders and put new rings, as I would expect after a teardown, then there is some break-in time to be expected?   

-dan

[Shadrach]

6 minutes ago, Bolter said:

@Ryan121b Is this still break-in operation time after the rebuild/post-strike inspection?  Cylinders will run hot when overhauled or new.  If they honed the cylinders and put new rings, as I would expect after a teardown, then there is some break-in time to be expected?   

-dan

Look at his data. They don’t run that hot. His fuel flow is clearly set on the low side. I think a large portion of his problems disappear by increasing fuel flow by 2 gph

[kortopates]

You must be getting massive leakage on the even side due to the wrinkles in the flexible baffling. To verify you need to shine a bright light in the air inlet with upper cowling in place. If it’s not laying flat against the upper cowling it’s leaking and that looks like a very large leak from the wrinkles.

FF will help but it won’t fix poor baffling.
Also FF won’t help a large imbalance between even and odd cylinders as the baffling suggest is present.

Sent from my iPhone using Tapatalk

[Ryan121b]

11 minutes ago, Fly Boomer said:

I don't have a 550, but that sounds dangerously low to me.  I would expect something in the 30s.  Maybe even mid-30s.

That's a good point, I've seen the other rocket / missile owners claiming 28.5 gph minimum, up to 30 gph for takeoff around sea level like where I'm based, so I will be increasing that in the near future which should help overall CHT temps. I was having an A&P pushing back on my higher FF request, since the Continental books advise 26.5 gph max, but it just isn't enough. Ideally my CHTs should be 380, or at least sub 400 on takeoff unless it's a hotter day. Hopefully the combination of better seals, higher FF will get me in a consistently safe CHT range.

 

[Ryan121b]

3 hours ago, Bolter said:

@Ryan121b Is this still break-in operation time after the rebuild/post-strike inspection?  Cylinders will run hot when overhauled or new.  If they honed the cylinders and put new rings, as I would expect after a teardown, then there is some break-in time to be expected?   

-dan

I have been running it in but only a handful of hours, I plan to complete the 25 hour break-in recommended by the Continental manual. I have been looking at the data but haven't seen a specific drop in temperatures across the board, and I'm still running on break-in oil at the moment.

[1980Mooney]

5 hours ago, Ryan121b said:

These photos are current day, the last photo is pre-strike inspection condition. Admittedly I knew little of the flexible baffle seals until recent troubleshooting, I'm concerned with the holes / wear from punctures on the left side of the engine, as well as the mis-formed section at the left rear of cylinder #2. On the back right side, the flexible seal is sliced, which seems like it was done to allow the seal to bend but also seems like it would allow far too much air through the back via all the gaps.

Pre-strike-inspection condition:

 

2 hours ago, kortopates said:

You must be getting massive leakage on the even side due to the wrinkles in the flexible baffling. To verify you need to shine a bright light in the air inlet with upper cowling in place. If it’s not laying flat against the upper cowling it’s leaking and that looks like a very large leak from the wrinkles.

FF will help but it won’t fix poor baffling.
Also FF won’t help a large imbalance between even and odd cylinders as the baffling suggest is present.

Sent from my iPhone using Tapatalk

• The baffling on the sides look fine (not sure about the "even side comment". 
  • You can put a dot of red RTV where the camloc's are wearing. 
  • Make sure that the shank on your camloc's are the right length.
• I can't see it in your pics but I always flip the front baffle up inside the lower cowl.  If you don't flip it up before you install the lower cowl it can be a pain to reorient.  It fits really tight
• The back baffle has a split seam in the middle - mine does not.  I would put a doubler on inside.
• The pilot's side of the rear baffle is a bit weird on all Missiles because that is where the wide nearly rectangular tube for the ram-air is bonded into the top cowling.
  • You will need a boroscope or something to see how it lays down then that flat tube pushes down.
• Also look at the top cowl to see the telltale marks where everything touches when it is bottoned up and pressing the baffling down
• Below is a pic (bottom) of another Missile from 
  • Missile Oil Drain Hose and fitting - Modern Mooney Discussion - Mooneyspace.com - A community for Mooney aircraft owners and enthusiasts
  • Notice that the front baffle (right behind the bottom part of spinner) is flipped up.
• Also my pic:

 

Edited December 8, 2023 by 1980Mooney