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Cylinder Woes - What Is the Lesson?


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Let me start off by saying, I LOVE my Bravo.  I just crossed the two year anniversary mark and my wife and I have had many great adventures, some of which, I've chronicled here.  In that time, I've flown over 300 hours, almost exclusively in the Bravo (with the exception of a TBM 700 and and and Extra 300 - just had to brag about that because it was so freaking cool!).  This is my fifth airplane and my fourth Mooney so I knew full well going into this ownership that there would be deferred maintenance to overcome and other wish list items to attend to during the first two to three years.  To date, I have performed the following maintenance / upgrades:

Overhauled:  Turbo, wastegate, exhaust, prop governor, main fuel pump, all six cylinders (progressively over the past two years on condition).

Upgraded:  Aspen PFD

Replaced:  starter, tires, shock disks, both magnetos and ignition harnesses (being installed now), one battery, autopilot computer, vernatherm

Repaired: TKS system, fuel leaks, dynamically balanced prop

Added:  Engine monitor JPI 830, GAMI injectors

 

The issue I am having has to do with the cylinders.  In March, I changed cylinder #5.  Since then, it has been running lean and warm so before my my most recent trip about two weeks ago from MS to Telluride and back, I removed the fuel injector and found it to be covered with oil although the plugs looked good (no oil there)...I cleaned it and had it checked over by the IA.  He seemed unconcerned but I was suspicious.   

Oil consumption was a little high on the trip out there - about 1.5 qts in 6.5 hours.  My engine usually burns one quart every 8 hours.  The day after the trip back, I checked the oil level again and I discovered that we burned 3 qts in 6.5 hours coming back.  I just delivered the airplane to the shop for an annual on Sunday and I informed the IA of the situation.  Today, I got "the call".  The #1 cylinder has low compression, 30/80, and the exhaust valve is burned.  I asked again about the #5 cylinder and the oil on the injector - he stated that oil blow-by from the #1 cylinder could have made it into the upper deck line and contaminated the injector for #5 (and others as well).  

The #1 cylinder was replaced with an overhauled one just shy of 300 hours ago in October 2018.  I run the engine with the following limitations:

WOT until 1000' AGL.

34/2400 cruise climb at 120 kts and <400 CHT's in the climb 

cruise at 29/2400 either 100 deg ROP or 30 deg LOP with CHT's around 360 - 380 (#5 is the new outlier here at 400) and TIT <1550

 

So, what the hell am I doing wrong here? 

What undiagnosed problem might exist? 

Is there a possibility that the oil cooling lines for the exhaust valve guides are clogged? 

Do I need to concede that LOP is not a good idea?

Did I just have bad luck with one overhauled cylinder (the main reason for the progressive replacement of all six was due to prior dormancy / corrosion and possible mis use by a previous owner)?  BTW, this particular cylinder was chromed which makes me wonder how old it really is.

What is the lesson here?

 

Thanks in advance for your whit and wisdom....

BTW:  I still LOVE my Bravo!

 

Alex

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Alex, your numbers are great operating parameters IMO. I would be more suspect of the overhaul of the cylinder itself. Valve geometry (assembled spring height, seat geometry, rocker to valve stem geometry, etc) are all very important for long life of the valve and guide. Cerma chrome or chrome hardened? I dont think you can even get a cerma chrome cylinder any longer, but could be wrong.

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4 minutes ago, mike_elliott said:

Alex, your numbers are great operating parameters IMO. I would be more suspect of the overhaul of the cylinder itself. Valve geometry (assembled spring height, seat geometry, rocker to valve stem geometry, etc) are all very important for long life of the valve and guide. Cerma chrome or chrome hardened? I dont think you can even get a cerma chrome cylinder any longer, but could be wrong.

Hi Mike,  the cylinder was channel chromed in 2014  by Aircraft Cylinders of America and apparently there it sat until it found its way to my engine in 2018.  

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Sounds kind of unique...
 

and...

Oil Going back through the intake is extra unique...

Sounds like a valve guide may be allowing oil to go where it isn’t supposed to be going...

Study up on the wet head plumbing if able... to best determine how oil got out of where it supposed to be, and into where it isn’t supposed to be...
 

A good drawing of the cylinder head may reveal some clues...

 

LOP and Bravos isn’t going to be an oil distribution problem...

The Bravo has the log style air distribution system instead of curvy balanced pipes... Not the best for LOP, but not a reason to leak or spread oil...
 

Often MSers like to take pictures of the valves from inside the cylinders... this can give us a hint of how well they are actually operating...

 

So... we know the cylinders have all been updated... exchanged or OH’d... but how are the valves working? Are they generating the nice pizza image of The effects uniform cooling?
 

Its possible a valve isn’t behaving properly... more likely on the cold end vs. the hot end...

There are 12 valves to select from... narrowing it down to one or two would make the next step a bit more precise....

Prepare to share some JPI data... just in case there is an odd sticky valve or something that shows up... that would help with the sleuthing work...
 

For something this unique... inviting @M20Doc to the conversation makes sense....

Dan @Danb recently took pics of his Bravo’s exhaust valves and posted them... possible that Dan may be familiar, but this seem pretty unique...

PP thoughts only, not a mechanic...

Best regards,

-a-

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The lesson...

Don't let your current ride know... that you have been cruising with the TBM...

There has got to be some jealousy in there somewhere...   :)

PP thoughts only, not a plane psychologist...

Best regards,

-a-

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22 minutes ago, carusoam said:

Sounds kind of unique...
 

and...

Oil Going back through the intake is extra unique...

Sounds like a valve guide may be allowing oil to go where it isn’t supposed to be going...

Study up on the wet head plumbing if able... to best determine how oil got out of where it supposed to be, and into where it isn’t supposed to be...
 

A good drawing of the cylinder head may reveal some clues...

 

LOP and Bravos isn’t going to be an oil distribution problem...

The Bravo has the log style air distribution system instead of curvy balanced pipes... Not the best for LOP, but not a reason to leak or spread oil...
 

Often MSers like to take pictures of the valves from inside the cylinders... this can give us a hint of how well they are actually operating...

 

So... we know the cylinders have all been updated... exchanged or OH’d... but how are the valves working? Are they generating the nice pizza image of The effects uniform cooling?
 

Its possible a valve isn’t behaving properly... more likely on the cold end vs. the hot end...

There are 12 valves to select from... narrowing it down to one or two would make the next step a bit more precise....
 

For something this unique... inviting @M20Doc to the conversation makes sense....

Best regards,

-a-

Here's a photo of the exhaust valve for cylinder #5 on 01/19 at 324 hours in service and 170 hours ago, pretty, huh?

BK8K0028.JPG.c0b9160d76389dd7c8638dfd7940ed04.JPG

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Suddenly, I’m feeling a bit hungry... :)
 

Alex, do you happen to have a pic of the intake valve?

Since, oil going back into the intake may be originating from The cold end of intake valve...
 

As far as how the seals work around the valve stem... more details I have forgotten... but would like to know now...

Best regards,

-a-

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2 minutes ago, carusoam said:

Suddenly, I’m feeling a bit hungry... :)
 

Alex, do you happen to have a pic of the intake valve?

Since, oil going back into the intake may be originating from The cold end of intake valve...
 

As far as how the seals work around the valve stem... more details I have forgotten... but would like to know now...

Best regards,

-a-

I mentioned two different cylinders and I think you might have them reversed in your mind.   #5 is the one that was replaced in March 2020 and has the oily fuel injector.  #1 is the one that was replaced in 10/18 and has the failing exhaust valve...the photo above is of #5 exhaust valve 01/19 about 170 hours ago.  Confusing to be sure.  I will get new photos of the intake valves, especially #5 when I am back at the airplane... and I will study a diagram of the cylinder  - anyone out there have such a thing to share?

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When I did the Bravo conversion in 2018 I had a set of first run cylinders from a Mooney owner that had around 800 hours on. I took them to J & J Airparts in Pleasanton TX, who has an excellent reputation on these cylinders. It took about six weeks though. It was almost $11,000 two and a half years ago to overhaul them. So far so good, I'm happy with the job they did.

My point is, though, that the parts are so expensive for this cylinder, and they have to be done by someone very familiar with them - if I had it to do over, provided they were in stock, I would have just ordered six new cylinders from Lycoming and been done with it. The potential savings in having other shops do it are quickly eaten up with the labor it takes to pull them, etc, etc, etc.

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1 hour ago, LANCECASPER said:

When I did the Bravo conversion in 2018 I had a set of first run cylinders from a Mooney owner that had around 800 hours on. I took them to J & J Airparts in Pleasanton TX, who has an excellent reputation on these cylinders. It took about six weeks though. It was almost $11,000 two and a half years ago to overhaul them. So far so good, I'm happy with the job they did.

My point is, though, that the parts are so expensive for this cylinder, and they have to be done by someone very familiar with them - if I had it to do over, provided they were in stock, I would have just ordered six new cylinders from Lycoming and been done with it. The potential savings in having other shops do it are quickly eaten up with the labor it takes to pull them, etc, etc, etc.

Funny you should bring that up because this particular cylinder is the last one that was NOT overhauled by J&J and that is who I called yesterday to order another overhauled one.  The issue for me with the new ones is that they are not immediately available....I'm just trying to get to TBO in about 650 hours at this point...

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  • 2 weeks later...

Something is not allowing the exhaust valve in Alex’s pic to uniformly get heat from the valve to the cylinder...

The uneven cooling lead to stickiness...

It also changes the color pattern from the round pizza looking valve to the less uniform look...

Is there a good valve job that can bring back the uniformity of cooling?

It might be lapping the valve seats... and extreme cleaning of the guides....
 

But, that is a holy cow amount of work to get the cylinders out and back...

PP thoughts only, not a mechanic...

Best regards,

-a-

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Alex, I am certainly no expert on lean of peak operations because I have never run anything lean of peak. But the weight of consensus about LOP operations as to this engine in this plane is that it shouldn’t be done. Have you had any discussion with anyone as to whether LOP operations could have caused or contributed to these problems? Your other operating parameters seem pretty typical and are how I run my plane. 

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8 minutes ago, Bravoman said:

Alex, I am certainly no expert on lean of peak operations because I have never run anything lean of peak. But the weight of consensus about LOP operations as to this engine in this plane is that it shouldn’t be done. Have you had any discussion with anyone as to whether LOP operations could have caused or contributed to these problems? Your other operating parameters seem pretty typical and are how I run my plane. 

@BravomanI've been wondering that very same thing.  In the absence of any other identifiable issues, I will have to concede that the whole LOP experiment was a failure.  I've always said that the most frequent source of my problem can be found by looking in the mirror!  FWIW, I am happy I went down the LOP road though because I taught me a lot about the engine.  I also confess that I might still fly LOP but at significantly lower power settings in the future (<65%) - because I am still enamored with the concept.

@donkaye, you're the among the most experienced and knowledgeable Bravo owners out there...do you adovcate LOP under any conditions?

Alex 

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Alex my Bravo has run ok lop when testing the engine to see if I could run lop., I’ve decided not just only due to my uncertainties. On your engine parameters it appears your numbers are fine. You’ve kept the cht’s under 400 plus ran her conservatively. The only difference being your lop operations. My friends at the airport believe in lop operations though. The unknown is how it was run prior to your ownership.

That said it doesn’t appear you’ve done anything wrong.

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From what I've read and experienced LOP ops don't burn valves.   Admittedly I've only owned my Bravo a couple of years and I'm a newbie compared to most.  It's my understanding most Bravos don't run smoothly lean of peak and utilizing GAMI injectors can take quite a bit of trial and error.  Therefore most run ROP.  I've never heard LOP is bad for our engines.   Mine runs well LOP with 25 hour borescopes showing exhaust valve heat distribution improving over time.   Certainly not saying I'm correct-just sharing my experience.  

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