Exhaust/turbo transition cracked

[Lee A.]

In the last 6 months I have cracked TWO exhaust/turbo transitions.  Exact same side and exact same location.  

Any ideas what might cause this?

m20TN Acclaim S TSIO-550

Dynamically balanced.  Runs smooth.  

Engine mounts replaced 2012 and mechanic says are OK.  

[KSMooniac]

Could they be mis-rigged such that there is a bending load being introduced when everything is tightened up?

Sent from my LG-US996 using Tapatalk

[carusoam]

Lee,

Got any pics of the crack or the installation?

Are you describing the first pipe that goes from the exhaust valve to the turbo?

How many hours on the exhaust system?  I realize one part is only 6months old.

Either way... if it is the pipe between the engine and turbo... there is no allowance for a crack to occur.  A very important safety issue with that.

Often with Mooney turbo exhausts, that first pipe sees a lot of heat related wear. The pipe wall thins out over time... but not 6months either...

Side thought, do you have a CO detector? Did it make an announcement? How did you find the crack?

PP thoughts only, not a mechanic...

Best regards,

-a-

[larryb]

What % power and TIT do you operate at?

[Lee A.]

Thanks for the responses so far....

Here is some additional data:

My mechanic discovered the cracked transition piece at annual 3 months ago.  He replaced it with a new ACORN brand piece.

I do fly with a CO detector.  I only noticed the very rare and brief alert of CO during a slow flight type of maneuver.

I always fly LOP and keep TIT less than 1600F.  I always let the turbos cool down during my 5 min taxi back to the hangar.

My mechanic discussed the issue with ACORN today.  Everyone's thoughts are the slip joints may not be slipping due to the mix of new/old parts and/or Continental/Acorn parts.

So the latest plan is to replace all the parts to the exhaust system on that side of the engine so new is matched with new and brand is matched with brand.

 

Don Maxwell chimed in on facebook recommending checking all the slip joints for proper operation which we have done and will do again.  He also recommended loosening the whole system and then retightening while tapping parts to minimize metallurgical stresses.  All good ideas.  I think TCM recommends this as well.

 

My mechanic indicates TCM/ACORN have a life expectancy of 700 hours on the transition piece as it endures a lot of heat and pressure.  My engine TT is 1800 hrs and top overhaul 800 hrs ago which may or may not have included the exhaust parts.   Either way, it appears I am well past 700 hours.  

As for the new transition which cracked at only around 40-50 hours.....I don't know for sure....

I don't have photos currently but have requested them because they will be educational for all of us.

[carusoam]

Lee,

Look for the use of a lubricant called mouse milk?

It may be mentioned in the lubrication of hot turbo related parts... sounds like cleaning the slip joints and lubricating their surfaces might be part of the process...(?)

PP thoughts only, not a mechanic....

Best regards,

-a-

[Lee A.]

Here are photos....

[carusoam]

Great pics, Lee!

Any idea what these few marks are?

(I put a white circle around the marks)

Looks like one is a casting leftover, the others look like some kind of left over cutting mark?

The position of the crack and the odd marks is the hottest spot in the exhaust stream... it is the spot where three waves of hot exhaust combine together... before entering the turbo...

These marks may have acted as a ‘stress multiplier’ causing and propagating the crack...

The same observations brought up before still apply.  There may be some stress being applied as the system is bolted together...

It sure found an interesting way to relieve the stress....

We have an MSer, that may be familiar with this particular exhaust pipe on TNIO550s, inviting @M20Doc

Best regards,

-a-

[Guest]

I’ve never seen one crack there.  It’s a Continental part, I would suggest contacting them to get input.

Clarence

[carusoam]

TSIO550 spec sheet...

http://www.continentalmotors.aero/uploadedFiles/Content/Engines/Gasoline_engines/550AvGas-SpecSheet.pdf

Without knowing the exact engine model or serial number, this is a guess... of the exhaust part...

http://www.continentalmotors.aero/support/illustrated-parts-catalog.aspx

 

Contacts page at CMI...

http://www.continentalmotors.aero/services/customer-tech-services.aspx

 

Best regards,

-a-

[StevenL757]

@Lee A., after reading through your posts, your mechanic appears to be on the right path and doing due diligence to get this sorted for you.  You're managing the engine correctly, so it's natural you'd be surprised something like this happened after only 40-50 hours following a piece replacement.  Without any other evidence, this sounds like more of an edge case.

Although I've no personal experience with ACORN exhausts (only what I've read and heard), the ACORN exhaust is a cost-effective and better way to go over the CMI factory exhaust, so doing a "brand-match" as he suggests is the way I would agree to go if faced with the same decision.  I do have a small piece of exhaust work to do this year at annual, so will keep ACORN in mind as a possible solution.

On a personal note...my IA and I work together not only at annuals, but regularly via mails and phone calls all year long (he's in TX, I'm in NY) to make sure the airplane and engine have the right things done when needed, and I know it isn't always cheap.  I consider myself one of the pickiest owners out there when it comes to maintenance, and I've chosen to work with him for many reasons...the biggest is that I trust him unequivocally to make the right decisions and help me maintain the ship to the best standard.  It sounds like your guy is acting in a similar capacity and is taking every step possible to make this right for you.  Hope I'm not stepping on toes, but at this juncture, I would let him go about the repair and trust he will make this right.

Happy to chat if needed...

Steve

[Lee A.]

Thanks for everyone's input.

After further evaluation, it does appear the Acorn piece is too long for the TCM piece.  My mechanic replaced the whole assembly with ACORN.  So far that is working well.

In addition, he ordered a replacement TCM piece (photo) and it appears TCM changed the shape/design.  I suspect these changes did not make it to ACORN, causing the incompatibility issue in my plane.

I fortunate to have very good mechanics to help with these issues.

[carusoam]

More great pics and input, Lee!

Thanks for sharing all the details.

Best regards,

-a-