First Bravo Annual PIREP

[alextstone]

Last September, I took delivery on my 95 Bravo.  At the time, it had 2420 hours TT and about 1100 Hrs since the last overhaul.  During the past 10 months,  I've had the following items overhauled:

1. Prop Governor
2. Turbocharger and wastegate
3. main fuel pump
4. one cylinder
5. TKS pump
6. entire exhaust system

I've had a number of other items repaired or replaced as well.  Last week, I took the aircraft in for annual.  At the time, I posted a photo on the FB Mooney page and mentioned that I would be doing some of the grunt work.  @mike_elliott, made the statement at the time to be sure to have a good look at the exhaust system.  I responded proudly that the exhaust had been recently overhauled so we should be all good there.  Well...herein lies the lesson to NEVER assume anything where aircraft are concerned. 

First, the number 3 cylinder failed the compression test.  Then the borescope inspection revealed a damaged exhaust valve.  This necessitated removal of the cylinder which in turn required the removal of the exhaust.  Here's a look at the valve:

During removal of the exhaust, it was discovered that a clamp that supports the section that connects the left and right sides  was installed incorrectly, causing chafing which would have certainly led to perforation.  The area that this clamp is installed is also the same area where the heater shroud is located so the cabin could have potentially filled with exhaust and CO.  Moreover, the problem was hidden by the intstalled shroud.

  

 

The clamp should have been installed to one side of the cable eye, not with the eye in the middle.  This caused the clamp to be loose.  

Lastly, we also found a hole in the air duct:

 

 

Lots to think about on this one...I am grateful these issues were discovered.

 

Alex

 

 

[MIm20c]

Alex take one of your old dental cameras and a small monitor and make a portable kit out of it. Twice a year I pull one spark plug per cylinder and look over the valves. Time well spent imo. 

[alextstone]

Alex take one of your old dental cameras and a small monitor and make a portable kit out of it. Twice a year I pull one spark plug per cylinder and look over the valves. Time well spent imo. 

I bought a borescope and I took photos of the valves about 100 hours ago. At that time, they looked normal so this damage occurred in the last 100 hrs. Your advice to look twice a year is appreciated and I will start doing that

Sent from my Pixel 3 XL using Tapatalk

[mike_elliott]

Alex, I always liked working on my plane and for the last 20 years of Mooney ownership, I would do my own oil changes every 25 hrs of course. I would take that opportunity to, cut open the filter, inspect the suction screen, mouse milk exhaust joints, visually inspect intake and exhaust, clean air filter, inspect for oil leakage, fuel leakage etc. I would remove plugs and borescope each cylinder and clean the plugs, re-anneal the copper plug gaskets, rotate and regap. Yep it took a 1.5 hr job and made it into a 5-6 hr job. I had the piece of mind of the condition of the engine going forward for another 25 hrs. It was probably overkill, but I enjoyed it and more importantly, it was a great time to put eyes on everything under the cowl.

 

[philiplane]

Burned exhaust valves in these engines are usually a byproduct of loose exhaust valve guides. Whenever you have a rocker cover off to change the gasket, check the valve stem for wobble. Excess stem to guide clearance will appear a few hundred hours before the valve burns.

[steingar]

I hate working on the Mooney.  Didn't mind at all wrenching on the Cherokee, did my own annuals and everything.  But the Mooney has about two hundred million screws, and they never seem to go back in the same way they came out.  Everything is crammed up in the engine bay.  I had an easier time wrenching on my sport bike..  I can see why mechanics are less than sanguine about working on Mooneys.

[carusoam]

Alex,

Great pirep!

Turbo exhaust challenges are more critical than NA exhausts...

Any leaks that occur before the TC are extra dangerous... because the exhaust is still under pressure... resulting in a cutting torch effect...

Then there is the CO that comes with all that.

Fantastic pictures too!

I Didn’t notice how wrong the cable support eye and clamp relationship is.  Glad you pointed that out too...

Best regards,

-a-

[daytonabch04]

Alex,

Thanks for the pics and PIREP.  My Bravo goes into annual in 2 weeks at DMax.  Wondering what all nuisances will come up.  I've had high CO readings from my FF Sentry, but haven't had the exhaust system looked at yet.  It'll be on my short list...

[Bravoman]

I know you run your plane lean of peak. Could the exhaust valve issue be due to that? I’m not a mechanic by any means so just asking but the folklore on the Bravo is to not run it LOP.

[carusoam]

Negative Bravoman... a penalty of five posts will be issued for spreading OWTs...    (just kidding...)

 

1) No... LOP doesn’t burn valves...

2) Bravos don’t like LOP as much as many other engines... but that is a vibration and uneven intake delivery more than anything else...

3) Take a look at curvy intake pipes on the IO550... equal length pipes delivering very similar air flow to matched fuel injectors makes things run smoothly LOP...

4) Now take a look at the IO540... a simple log intake... not much balance except for at one LOP setting, not like the range that the other planes get with the curvy same length tubes...

5) 4 cylinder engines are so much easier to balance the intakes of...

6) If JPI data is available... we might be able to see what was happening before the valve got damaged...  there are signs of stickiness that come before the valve stops rotating... 

7) when the valve stops rotating the heating and cooling isn’t spread out very uniformly...

 

Well That’s What It looks like when this happens... valves stop rotating, then they lose their Pizza image...

 

On another note... if you are seeing elevated CO levels on your monitor... it is important to take a look at what is causing it...

TC’d engines can be more hazardous to life and limb than NA planes...

Keep in mind, it might be entering the cockpit from a leaky seal...

Best regards,

-a-

[alextstone]

Here’s the engine data link from a recent flight...

 

https://savvyanalysis.com/flight/3291811/22c074b0-02e6-45cd-a8fe-0b6974335332

[carusoam]

Alex,

That’s a nice looking flight... that was June 23... did the valve problem happen after that? Looks like it may have...

What I was hoping to point out was... the effect of the sticky valve... on the graph...

The EGT line of a sticky valve usually has a sawtooth pattern associated with it... it really stands out as an irregular pattern... when compared to the other five cylinders...

In this one flight, the valve isn’t obviously misbehaving as I would have expected...

one other oddity in the graph that I see... the TIT data dropped off line a few times at the end of the flight after landing... just something to watch for if there is a loose connection doing that(?).  Or it might be something TCs do(?)

See if Paul @kortopates is around... he has some really good experience at reading these things... (heat damaged valve in an M20M TSIO540)

 

PP thoughts only, not a mechanic...

 

Best regards,

-a-

[alextstone]

6 hours ago, carusoam said:

Alex,

That’s a nice looking flight... that was June 23... did the valve problem happen after that? Looks like it may have...

I’ll pull the other data from the JPI when I am back to the plane to check but that flight was very recent.  I would have hoped that there would be an indication of impending failure by then.

6 hours ago, carusoam said:

What I was hoping to point out was... the effect of the sticky valve... on the graph...

The EGT line of a sticky valve usually has a sawtooth pattern associated with it... it really stands out as an irregular pattern... when compared to the other five cylinders...

In this one flight, the valve isn’t obviously misbehaving as I would have expected...

one other oddity in the graph that I see... the TIT data dropped off line a few times at the end of the flight after landing... just something to watch for if there is a loose connection doing that(?).  Or it might be something TCs do(?)

Yes, I was aware of the TIT indication issue,. I suspect a loose connection.

6 hours ago, carusoam said:

See if Paul @kortopates is around... he has some really good experience at reading these things... (heat damaged valve in an M20M TSIO540)

Paul already analyzed a recent flight for me inside my Savvy account about 6 or 8 weeks ago.  At that time, no issues were found.  I suppose the take home message is that there is no one data source that tells all.  

6 hours ago, carusoam said:

 

PP thoughts only, not a mechanic...

 

Best regards,

-a-

I 

[mike_elliott]

On 8/14/2019 at 4:10 PM, steingar said:

I hate working on the Mooney.  Didn't mind at all wrenching on the Cherokee, did my own annuals and everything.  But the Mooney has about two hundred million screws, and they never seem to go back in the same way they came out.  Everything is crammed up in the engine bay.  I had an easier time wrenching on my sport bike..  I can see why mechanics are less than sanguine about working on Mooneys.

Yes, it does take a good A&P to wrench on a Mooney, not for your average Cherokee wrench.

[Davidv]

On 8/15/2019 at 11:15 PM, carusoam said:

On another note... if you are seeing elevated CO levels on your monitor... it is important to take a look at what is causing it...

What would you see as a concerning CO level in cruise? I took a flight yesterday from FL to NH at 17.5k and for most of the flight I was seeing 4-5 on the indicator, at one time during the flight it went up to 14 for 5-6 minutes and then settled down to 0 for the last 1.5 hrs.  I saw a little correlation between when I had the cowl flaps cracked open and then closed them and it settled down to 0-5.  I just bought my CO monitor last month and have generally seen 0 in cruise.

[carusoam]

@Davidv 

There are two or three typical CO levels that have been reported...

1) really low... 0-3 typically seen in cruise...

2) Something causing an elevated level... 4-10 (possibly exhaust getting into the cabin, past a seal...)

3) larger numbers when exhaust leaks in front of the firewall...

There are a few threads around here of people who have searched and found their CO leak... one was an interesting missing seal where cables enter the cockpit from the tail...

MS has a really good CFI with first hand experience with CO... See if Dan / @DanM20C is around for additional insight...

PP thoughts only, not a mechanic....

Best regards,

-a-

[Davidv]

Thanks!  The weird part for me is how it went up and then came down, I turned heat on and off and if anything that seemed to lower it a few which was weird. I know very little about this subject but I could see where the flaps open (especially in a climb) could potentially cause a tiny bit of exhaust to be mixed with the cabin air inlets but maybe I’m off base.

[DanM20C]

13 hours ago, carusoam said:

MS has a really good CFI with first hand experience with CO... See if Dan / @DanM20C is around for additional insight...

I don't really have any additional insight.  The brain trust on MS has probably the best handle on CO in aviation than any other source.  Thanks to Anthony we get it summarized into easy to understand posts.

I recommend anything consistently above 5ppm should be investigated further.  The CO isn't a danger at this level but it may be an indicator of something failing.   Recently someone reported to me he noticed a small rise and found an exhaust slip joint that had partially separated.  Upon further investigation he found that it had partially separated because one of the engine mounts had broke and the engine had shifted. 

Cheers,

Dan