bad in flight mag check, potential exhaust valve abnormality - next steps?

[DXB]

To make a long story somewhat short:  O-360-A1D.  Run up on ground - normal.  In cruise, I normally lean to keep my hottest cylinder (#2) at 380 or less.   When leaning for cruise, I notice my #2 CHT is 30 degrees cooler than usual, whereas  EGT was a tad hotter.  So I lean and then do an in flight mag check - yikes - left runs very rough, #2 EGT goes cold.  While I'm pondering ending the flight, the #2 EGT/CHT start fluctuating, and the left mag check becomes intermittently normal vs. rough.  After 20 minutes, the mag check becomes normal, and I continue to my destination.  After landing, I do another run up that is again normal.  On the 2 hr return flight the next day, everything is normal including in flight mag checks - I pulled the JPI data for the two flights after returning and sent to Savvy Analysis to be sure.  I'm guessing what happened here is that the #2 bottom plug fouled at some point between run up and leveling off for cruise, although I thought it was unusual to have it foul at full power in climb, and I do lean aggressively on the ground. Of note, whenever I've had a fouled plug, it's always been bottom #2. Bendix mags were IRAN'd 100 hrs ago.

Question #1: Am I reasonable in writing this off as a spark plug issue?  Should I be worried about anything else?

Today I pulled the bottom #2 plug (I have Tempest UREM37BY massive plugs with 90 hrs on them).  There was no oil on it. Resistance test was normal. It had some heavy lead deposits, which I picked off.  I narrowed the gap from >.22  to 0.16.  I always borescope my valves with a cheap dental camera when I pull plugs. The images are not great, but I've previously never seen anything concerning. But this time, my #2 exhaust valve had a small darkened crescent at one edge where deposits have clearly flaked off  (pic below). I can't get a decent view of the valve seat at that location. Poor man's compression test based on turning the prop seems fine. I've never had any sign of morning sickness.  A recent Savvy FEVA analysis of my JPI data was fine and is being repeated now.  Assuming that's ok, my plan is to do nothing further now.  At annual in 2 months, I will ask that they do the following: (1) repeat borescopy with a better camera (2) listen carefully for exhaust leak on #2 during compression testing (3) wobble test that valve.  I'll be prepared to pay to ream that valve guide vs. IRAN that jug with replacement of valve, guide, and seat if warranted. My jugs are first run Millenium cylinders with ~900 hrs on them.  #1 had to be IRAN'd for a bad exhaust valve when I bought the plane 2 years ago with 700 hrs SMOH.  It didn't have an engine monitor prior to my owning it, and so I have a feeling previous owners  couldn't pay adequate attention to CHTs.   

Question #2: Is my plan reasonable? Should I do something more urgently? Should I do something different?

Question #3: Can someone please recommend a really trustworthy shop in my general area with excellent engine work acumen?  I've had some negative experiences 

 

[rbridges]

Sorry but I don't have any insight.  I'm really interested in how this turns out.  I'd like to learn from your experience.

[smwash02]

Unless you've got other issues mag wise, I'd write it off to abnormal fouling.

Cylinder wise -- I've gone through 2 (technically 3) cylinders in the 300 hours I've owned mine. Both cylinders were in the 600-700 hour range. Both had cooked exhaust valves.

Your camera shows it's starting to leak. It would be nice to see the whole valve for comparison if you have it, but bottom line is the leak will not get better. You are going to have to start planning to replace it.

The last one I replaced gave me 30-40 lbs so I lapped it in place bringing it to 68 and put another 40-50 hours on it until it felt weak during my regular 'poor man's compression check'. It was back to 40 so I pulled it. You've caught yours early, if you do something with it now you can get more time than I got out of mine. Your plan to do a wobble test is what I'd do as well.

As to how immediately you take real action... It's really the amount of risk you want to take on. You know it's 'bad' and on the bench wouldn't be airworthy. Personally, I'd do the wobble test, clean up the valve seat, and watch for the area to expand or compression to dip below 60 then replace it.

Having a C I know the pain of replacing a jug. One of the ones I replaced had bad valves 30 hours after I installed it, so I got to do that one twice. I wish you the best.

[carusoam]

EGT getting hot while CHT getting cold is a typical response of a plug not working 100%.  Raw fuel is not getting burned in the cylinder, but it is getting burned down stream.

The lead balls that collect in the bottom plug can be minimized by leaning as much as possible on the ground.

Having fine wire plugs will help with the leaning.

Unfortunately, without before and after pictures I can't see the usual pizza looking valve photo.  But if it isn't the usual pizza looking valve like the others, there is something to look into...

39N is where my C used to go for this type of work... Want some contact details?

do the search on wobble test and the rope trick for cleaning carbon out of the valve guides. For an extra scare read about a stuck valve in My C...  that occurred in my first 10 -20 hours of ownership or so...

PP ideas I learned here on MS.  Not a mechanic...

Best regards,

-a-

[ArtVandelay]

I lean during climbs as well, try to keep 100-150 ROP, better performance and easier on the engine than full rich the whole way up.

[bradp]

Would someone experienced by able to explain in detail what the wobble test is actually measuring?

My impression is that it is measuring the ability of the valve stem to move laterally within the valve guide...  The problem with our lycoming valves is poor distribution of oil to the valve train and poor dissipation of heat.  The oil on the valve stem / within the guide becomes coked and carbon deposits form on both guide and stem.   By this account, I'd expect a tolerance for how much lateral movement normally occurs at the key end of the stem: too little movement may indicate coking and would limit proper oiling.  Too much movement may indicate that the valve guide is worn. Is this the correct reasoning? 

Second question- why and how do the valves rotate during each closing?   If DXB does have build up of carbon on one face of the valve, does this indicate a lack of  rotation of the valve or corrosion along the specific part of the valve seat?  How can EGT data Point to a problem with an exhaust valve? 

[Yetti]

Seeing one of your valves on #2 cylinder removed with a punch and hammer would help you know why a wobble test is a good thing.

 

[DXB]

15 hours ago, teejayevans said:

I lean during climbs as well, try to keep 100-150 ROP, better performance and easier on the engine than full rich the whole way up.

Yeah I always try to lean to a target EGT in climb once above about 4000msl, but don't get very far without approaching a CHT of 400 on my hottest cylinder.  I'm still a little puzzled by how I fouled so badly during climb.

23 hours ago, carusoam said:

Unfortunately, without before and after pictures I can't see the usual pizza looking valve photo.  But if it isn't the usual pizza looking valve like the others, there is something to look into...

39N is where my C used to go for this type of work... Want some contact details?

Yeah they are pizzas, but #2 is a pizza where someone took a little nibble at the crust .   I guess if the valve is sloppy in the guide on wobble test, the jug is likely coming off and getting IRAN'd - I've heard guides can be changed without pulling it and I need to learn more about this, but it seems like an incomplete solution at first glance. I hate the risks that come with major invasive engine work, but I have zero appetite for risking valve failure either. If the wobble test is normal, what to do seems less clear. I'm hoping to find someone who's really good at this stuff and welcome any recommendations.  Anthony- I'm sending you a PM.

[par]

I hope you figure out your issue. I normally do not lean until I am leveled off and pull the prop back to 2500 or lower. If I try to lean in the climb, I notice CHT's easily exceed 400 on 2, 3, and 4. Once the engine is leaned out at my causing altitude, #2 and #4 run between 380-400. I have also noticed that the slightest amount of leaning or richening at this point can make the difference between exceeding 400 in any given cylinder. I will most likely OH the carb at some point in the future but the engine runs well for the moment and I'll take that for now.

[DVA]

There’s no such thing as normal fouling. There is however such a thing as acceptable fouling - you find that in otherwise perfectly airworthy engines that are just getting older. The key is, find out why you are fouling, if in fact you really are.

Bottom plugs have gravity working against them so oil will tend to end up near them, but you need a fairly good quantity of oil above the piston to create any adverse effects. This condition is abnormal.

If you have oil slowly leaking through the valve guide it may take some time for that to fully clear out and burn away. As the engine gets hotter the various tolerances change often times making things better (or worse) which may be why you had a rough run for a short amount of time and then things got good again. If you’re leaking a little oil through the valve guide on that #3 cylinder, I personally would not worry as long as the wobble is in tolerance, but if your valve is burning away, I would be concerned.

To me, your valve looks like it is leaking, and since valves rotate around (due to vibration) during operation, I would expect it is the valve itself that has a defect instead of the seat. If the seat had a defect, the valve would likely have a symmetrical burning to it. It would be interesting to run the engine for a few moments and then look again. You’ll probably see the burn area displayed at a different angle and maybe you can rotate the prop, open the value and get a better look at the bottom of the value. There may be a small deposit that can be safely scrapped away that is causing a slight leak, or you may notice a chip or small piece missing. If you saw that, I would definitely seek a repair right away.

Let us know how you make out.

DVA 

[DXB]

On 10/20/2016 at 6:31 PM, DVA said:

. It would be interesting to run the engine for a few moments and then look again. You’ll probably see the burn area displayed at a different angle and maybe you can rotate the prop, open the value and get a better look at the bottom of the value. T

Yeah this a really great idea - more to follow...

[DXB]

Need more expert advice.  I watched my problem for a while - the engine still seems to run like a top, and downloaded EGT trace still looks normal.  Then I imaged #2 exhaust again:

Bugger!! Unequivocal green mold at the edge of the burnt pizza.  That #2 exhaust valve is definitely burnt. I might be seeing it sidestep also when it seats, though I'm not sure.   Now when I pull the prop through for the "poor mans compression test," #1 and #4 feel very firm.  #3 is softer.  #2 is much softer and gives a loud hiss at the exhaust.

And now I have ANOTHER problem - oil consumption over the last year has gradually gone from 1 qt / 7-10hrs to 1 qt/ 5hrs. But in the last few weeks it then jumped to 1 qt/ <3hrs, and the oil got dark FAST after changing 10 hours ago. So I'm convinced it's blow by, not leaking or burning.  It'd be nice if the blowby problem were also on #2 so I could just pull one jug, but I'm afraid it's not.  The bottom plug on the #3 cylinder (the 2nd softest one to pull through) always has oil on it now, and my borescope got oily in there, though the valves looked fine.  Anyway, I can't justify flying it much longer, and I've scheduled an annual 1 month early at a shop recommended by a fellow Mooneyspacer.  

Questions:

1. Am I correct in thinking the blow by problem is likely mainly on #3?  Or could it be that #3 mainly has an oil control ring problem, and the blowby could also be on #2?   But then I'd think that I wouldn't hear such a loud hiss at the exhaust when pulling #2 through TDC.  

2. If I need to pull off both #2 and #3, am I best off going to an engine shop instead? Mike Busch recommends this if pulling more than one jug, and my maintenance-induced failure anxiety is as high as anyones.  

3. What questions should I ask my shop before they do this very invasive work? 

 

[LANCECASPER]

On 10/16/2016 at 1:37 PM, DXB said:

 . . . So I lean and then do an in flight mag check - yikes - left runs very rough, #2 EGT goes cold.  

 

 

Call me cautious but I am not a fan of in flight mag checks. Scenario . . .If you switch to L and and your only good mag was the R mag - not something I want to deal with in the air.

Back in '99 I was flying a Bravo over Metro Atlanta and the engine started running rough. I asked a much wiser more experienced pilot who was in the passenger seat, "What do you think?". He said, "I think I see an airport". We landed at Peachtree Dekalb and sorted it out on the ground. It ended up being a bad mag and got it replaced the next day. Even though we had some altitude I was happy we verified that on the ground, not over Buckhead.

[gsxrpilot]

I was always afraid of inflight mag checks until I went to the APS class. Now I do them religiously and am quite comfortable.  

You should be able to diagnose the wobbly valve by looking at the JPI data. If you've uploaded it to Savvy, do you mind posting a link to it here?

Your inflight mag check result is classic plug fouling and I wouldn't worry about that at all. 

[Browncbr1]

After reading about your blow by and valve, it seems to me that the valve issue may be a symptom of the rings moving around and letting loads of oil into the combustion chamber and gobbing up the valve seat and guide...  Perhaps excess oil was also fouling your plug.   I wouldn't put too much stock in the compression test.  

Edited December 2, 2016 by Browncbr1

[Wakeup]

I have never done a mag check in the air.  Is the procedure the same as on the ground?  Just turn the key and pray it runs smooth.   Thanks. 

[Hector]

I have never done a mag check in the air.  Is the procedure the same as on the ground?  Just turn the key and pray it runs smooth.   Thanks. 

Yeah, I don't do them routinely but if I sense anything, even just a slight roughness I'll check. Had a mag p-lead go bad in flight not long ago and started running a little rough. Switched from "Both" to "R" and got 100 rpm drop. Back to "Both" then "L" and engine quit. Back to "Both" quickly and engine started immediately. I do routinely do a mag check now prior to shutdown.

[Marauder]

I have never done a mag check in the air.  Is the procedure the same as on the ground?  Just turn the key and pray it runs smooth.   Thanks. 

The lean mag check inflight is a bit more than the ground check. You run the engine for a minute on each side with a minute on both in between. Here are the instructions for both the GAMI and inflight mag checks: http://content.savvyanalysis.com/static/pdf/SavvyAnalysisFlightTestProfiles.pdf

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[carusoam]

Dev,

how long has it been since the cylinders have been OH'd?

The rough cross-hatched surface may be missing. Rings can be worn...

Check the price of getting an OH'd cylinder put in place.  See if there is a discount for two or four...

The fungus on your pizza doesn't look very appetizing.

Blow by does two things, turns the oils dark, really quickly,  and blows it out the vent line at the same time.  It also makes the oil smelly, like exhaust...

OH'd cylinders with your well cared for carburetor should run really nicely.

At a minimum, consider getting the valve guides cleaned and wobble checked.  See if there is any carbon built up in the guides.  There are a few threads on reaming out the valve guides...

On the C, the front two cylinders usually see better cooling than the back two...

Best regards,

-a-

[DXB]

10 hours ago, gsxrpilot said:

I was always afraid of inflight mag checks until I went to the APS class. Now I do them religiously and am quite comfortable.

You should be able to diagnose the wobbly valve by looking at the JPI data. If you've uploaded it to Savvy, do you mind posting a link to it here?

I like the inflight mag check but agree that having it quit on one side would be hair raising.  If that happens on the carb'd plane, one also has to remember to pull the throttle well back before returning to the good side to prevent a backfire.

I don't think the issue with #2 exhaust is far enough along to see on the EGT trace- my impression is that this is a fairly advanced sign. But the borescope view is pretty damning. I did have Savvy look a little while ago.  I think it's a good tool, but honestly I am skeptical how sensitive looking at EGT alone is - when you see the oscillating pattern, it is alarming but may give false security  if normal.  I'm thinking my #2 cyl. should come off  based on the borescope view alone.  But here's a link to a recent flight:

https://www.savvyanalysis.com/flight/1648114/63090bd1-31af-423c-af56-9fe795df9873

9 hours ago, Browncbr1 said:

After reading about your blow by and valve, it seems to me that the valve issue may be a symptom of the rings moving around and letting loads of oil into the combustion chamber and gobbing up the valve seat and guide...  Perhaps excess oil was also fouling your plug.   I wouldn't put too much stock in the compression test.  

I agree except the oily plug is on #3 but the burnt-looking exhaust valve is on #2, so I'm not sure they are related events.  Either way #2 is coming off, and I'm trying to decide on #3.

7 hours ago, carusoam said:

how long has it been since the cylinders have been OH'd? Check the price of getting an OH'd cylinder put in place.  See if there is a discount for two or four...

OH'd cylinders with your well cared for carburetor should run really nicely.

At a minimum, consider getting the valve guides cleaned and wobble checked.  See if there is any carbon built up in the guides.  There are a few threads on reaming out the valve guides...

On the C, the front two cylinders usually see better cooling than the back two...

 Anthony - my cylinders were new Millennium at major overhaul in year 2000, now with >850 hrs on them.  Only #1 got IRAN'd 250 hrs ago when I bought the plane because of a bad exhaust valve- it's been great since then.  #1 and #4 feel so solid for compression and the valves look great on borescope, so I'm not going to touch them unless the mechanic finds something (I'm actually going to the folks you suggested). I'm gonna need some advice from them on #3. I'm betting the blow by is on #3 and possibly #2.   I'm inclined to IRAN and not overhaul or get a new cyls if they are basically in decent shape - will probably rehone, get new rings, new exhaust valve and guide, grind the seat - this minimalist approach worked great for #1.   Not surprisingly, #2 is my hottest cyl by about 20-30 degrees in cruise- hence the valve issue on it.  It's not the leanest, so gotta be something with the baffle.  I do work to keep it under 380, but who knows how the previous Texas owner ran it - and it had no real engine monitor when I got it.  

 

[Marauder]

Dev -- before I went whole hog on an aggressive approach, I would try to get better pizza pictures. I have a pretty decent borescope that articulates and will allow you to get a full picture of the valve. You are more than welcome to use it. Let me know. Here is a picture of one of my pizzas.




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[Marauder]

It's even got enough resolution to read the Lycoming part number.




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[gsxrpilot]

When doing a proper inflight mag check... if the engine quits on one of the two mags, it's important to pull the mixture all the way out before switching back to both mags. The slowly advance the mixture until the engine comes back to like. A backfire in a small bore carbureted four cylinder is one thing, but in a high hp large bore, you can blow the exhaust system apart.

[Marcopolo]

DXB,

 

  Going with the theory of not pulling multiple jugs simultaneously, why not pull them one at a time meaning only having one jug off at a time.  This should keep the case torqued and aligned properly but it will increase your downtime.  You could even buy a cylinder up front to put on as you take one off and then only wait on the second one.  Just a thought...or two.

 

Ron

[DXB]

6 hours ago, Marcopolo said:

DXB,

 

  Going with the theory of not pulling multiple jugs simultaneously, why not pull them one at a time meaning only having one jug off at a time.  This should keep the case torqued and aligned properly but it will increase your downtime.  You could even buy a cylinder up front to put on as you take one off and then only wait on the second one.  Just a thought...or two.

 

Ron

Interesting- just trying to get my head around how this stuff works and the risks involved.  I imagine one could put on a dummy cylinder also in some form in place of the first one while pulling the second one off...?