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Mooney Bravo Weird Compression Issue

irishpilot
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irishpilot Proficient

irishpilot

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Hey all, my A&P and I are kind of stumped on what could cause a weird compression issue. I took the plane in for a mild engine surge at 38"/2575 during the first few hundred feet of climbout. We combined this with the annual inspection and that's where my A&P found the #2 cylinder showed 5 psi on cold compression check and 10 psi on the hot. I've been flying the plane a lot (15 hrs/mo), and there was no indication on the JPI. CHT and oil consumption normal and no engine roughness. The engine is a TIO-540-A1FB. Attached is a recent flight at 17,000'.

Anyone know what would cause such low compression with no other associated indications? The A&P is pulling the jug today but I want to be sure there isn't some A1FB specific causes that could cause this. Thanks!

IMG_20200528_073044_01.jpg

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gsxrpilot Grand Master

gsxrpilot

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2 hours ago, irishpilot said:

I don't have that darn male USB cable. I'm trying to tack one down so I can pull the data.

Sent from my Pixel 3a using Tapatalk
 

I keep one of these with a USB stick in my flight back to download after most flights.

https://www.amazon.com/LUTIONS-Type-5-Pin-Female-Adapter/dp/B071R841Z3/ref=sr_1_6?crid=QT5WW0PEO8L5&dchild=1&keywords=usb+mini+to+usb+adapter&qid=1590687242&sprefix=usb+mini+to+usb+a%2Caps%2C163&sr=8-6

 

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David Lloyd Mentor

David Lloyd

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When a cylinder is leaking like that the hissing air is obvious. You will hear it coming from the crankcase (breather or oil fill) if it is the rings.  Exhaust pipe if an exhaust valve or the intake if an intake valve.  Gives a big head start on where to look.

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alextstone Mentor

alextstone

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15 minutes ago, philiplane said:

Ring alignment will not produce compression that low. A bad exhaust valve will. Borescope it before flying. It could be to the point where the valve head separates, and then you'll need a lot more than one cylinder repair.

That's the best advice you could get....

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irishpilot Proficient

irishpilot

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Awesome! Just ordered.

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Bolter Mentor

Bolter

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Summarizing a few questions that were already posted because I think a good process for diagnosis is important when the JPI shows no running issues.  And removing a cylinder tends to turn into replacing the cylinder, after all, you already have it off...

  1. Where was the air going during compression check?  With no telltale of air, I would be rechecking the tools and the process before committing to removing the cylinder.
  2. Was a borescope inspection done before deciding to pull the cylinder?  Not all things will be seen with the scope, but some major ones can be.  

With my day job, more costs are at stake (but it is not my money) and detailed inspection and diagnosis has been very useful.  

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PT20J Grand Master

PT20J

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I’d forget the JPI. With that much leakage, something is messed up. Like others said, find out where the air is getting out (which should have been the first thing the A&P did). 80 psi escaping is pretty noisy.

Skip

 

 

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carusoam Grand Master

carusoam

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Pics of the valve will be interesting...

Doesn't cost much to get...

Would like to compare to another Bravo that posted their pics a while back...

Valves not seating can cause a loss of compression...

Having compressed air escaping through the exhaust system should be recognizable...
 

1) Data

2) valve pics

3) then decide next steps...

PP thoughts only... not a mechanic...

Best regards,

-a-

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bradp Grand Master

bradp

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6 hours ago, RLCarter said:

I would bore scope it, if nothing obvious go fly it for an hour and re-check it

Definitely scope it before pulling the jug.  Ground run and retest to ensure it’s not a process issue.  

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philiplane Mentor

philiplane

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Testing by the engine manufacturers confirm that a cylinder can have virtually zero static compression, yet make full rated power. Oil consumption will be high, but your engine monitor may not show any differences, right up to the point the exhaust valve head fails.

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Bolter Mentor

Bolter

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2 hours ago, philiplane said:

Testing by the engine manufacturers confirm that a cylinder can have virtually zero static compression, yet make full rated power. Oil consumption will be high, but your engine monitor may not show any differences, right up to the point the exhaust valve head fails.

As I understand it, in that situation (fails compression but makes power) a good view of the valve face sealing surfaces with the borescope would indicate exhaust valve issues. 

Read that as a question, though it ended without a question mark.

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alextstone Mentor

alextstone

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10 hours ago, philiplane said:

Testing by the engine manufacturers confirm that a cylinder can have virtually zero static compression, yet make full rated power. Oil consumption will be high, but your engine monitor may not show any differences, right up to the point the exhaust valve head fails.

@philiplane  right on.  Here's a link to my post showing what the engine monitoring looks like in real time DURING an exhaust valve failure....

 

 

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LANCECASPER Grand Master

LANCECASPER

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6 hours ago, irishpilot said:

Kurt Willman at Stinson. The plane is hangared there as well.

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The TIO-540-AF1B is a very unique engine - the only airplane in the world that uses it is the M20M. It's usually a lot more expensive to pay someone to learn about this engine than to go to someone who's very familiar.

Plus it's not a bad idea once in awhile to get a fresh set of eyes on it. Within a 1.5 M20M hours of San Antonio there are four good options that have worked on many Bravos: Don Maxwell in  Longview TX (KGGG), SWTA in Smithville (84R), Dugosh in Kerrville (KERV) and Ron Fisher up in Kestrel Airpark (1T7).

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