Exhaust leak at ball joint

[M20C Driver]

Question.  I had the side cowl off to address my exhaust hangar and noticed some discoloration on a section of scat tubing adjacent to the ball joint.  Looks like it is coming from this one area.

 

My questions are: 1) Is this beyond the scope of FAR 43.3 or is it considered allowed owner maintenance?  2) If allowed as owner maintenance is it usually a matter of disassembling , lubricating joint and reassembling with new hardware to fix the leak?  
The exhaust system itself is in good shape.  I replaced it with a brand new one 3 years ago.

Thanks in advance for the insight.

[Shadrach]

Your picture is not very helpful at highlighting the problem you’ve described. I can’t tell if I am looking at the spring tensioned nut and bolt for the ball joint of an exhaust header on a Hanlan and Wilson exhaust system or the tail pipe ball joint coming off the the muffler on the Mooney exhaust system (both H&C and Mooney systems were fitted to C models). I assume the out of focus orange shape in the background is scat tube. 
 

Do you have an image that is more zoomed out?
 

Below is the list of repairs that a pilot is authorized to perform on an aircraft operated under Part 91.

 14 CFR Part 43 appendix A

(c) Preventive maintenance. Preventive maintenance is limited to the following work, provided it does not involve complex assembly operations:

(1) Removal, installation, and repair of landing gear tires.

(2) Replacing elastic shock absorber cords on landing gear.

(3) Servicing landing gear shock struts by adding oil, air, or both.

(4) Servicing landing gear wheel bearings, such as cleaning and greasing.

(5) Replacing defective safety wiring or cotter keys.

(6) Lubrication not requiring disassembly other than removal of nonstructural items such as cover plates, cowlings, and fairings.

(7) Making simple fabric patches not requiring rib stitching or the removal of structural parts or control surfaces. In the case of balloons, the making of small fabric repairs to envelopes (as defined in, and in accordance with, the balloon manufacturers' instructions) not requiring load tape repair or replacement.

(8) Replenishing hydraulic fluid in the hydraulic reservoir.

(9) Refinishing decorative coating of fuselage, balloon baskets, wings tail group surfaces (excluding balanced control surfaces), fairings, cowlings, landing gear, cabin, or cockpit interior when removal or disassembly of any primary structure or operating system is not required.

(10) Applying preservative or protective material to components where no disassembly of any primary structure or operating system is involved and where such coating is not prohibited or is not contrary to good practices.

(11) Repairing upholstery and decorative furnishings of the cabin, cockpit, or balloon basket interior when the repairing does not require disassembly of any primary structure or operating system or interfere with an operating system or affect the primary structure of the aircraft.

(12) Making small simple repairs to fairings, nonstructural cover plates, cowlings, and small patches and reinforcements not changing the contour so as to interfere with proper air flow.

(13) Replacing side windows where that work does not interfere with the structure or any operating system such as controls, electrical equipment, etc.

(14) Replacing safety belts.

(15) Replacing seats or seat parts with replacement parts approved for the aircraft, not involving disassembly of any primary structure or operating system.

(16) Trouble shooting and repairing broken circuits in landing light wiring circuits.

(17) Replacing bulbs, reflectors, and lenses of position and landing lights.

(18) Replacing wheels and skis where no weight and balance computation is involved.

(19) Replacing any cowling not requiring removal of the propeller or disconnection of flight controls.

(20) Replacing or cleaning spark plugs and setting of spark plug gap clearance.

(21) Replacing any hose connection except hydraulic connections.

(22) Replacing prefabricated fuel lines.

(23) Cleaning or replacing fuel and oil strainers or filter elements.

(24) Replacing and servicing batteries.

(25) Cleaning of balloon burner pilot and main nozzles in accordance with the balloon manufacturer's instructions.

(26) Replacement or adjustment of nonstructural standard fasteners incidental to operations.

(27) The interchange of balloon baskets and burners on envelopes when the basket or burner is designated as interchangeable in the balloon type certificate data and the baskets and burners are specifically designed for quick removal and installation.

(28) The installations of anti-misfueling devices to reduce the diameter of fuel tank filler openings provided the specific device has been made a part of the aircraft type certificiate data by the aircraft manufacturer, the aircraft manufacturer has provided FAA-approved instructions for installation of the specific device, and installation does not involve the disassembly of the existing tank filler opening.

(29) Removing, checking, and replacing magnetic chip detectors.

(30) The inspection and maintenance tasks prescribed and specifically identified as preventive maintenance in a primary category aircraft type certificate or supplemental type certificate holder's approved special inspection and preventive maintenance program when accomplished on a primary category aircraft provided:

(i) They are performed by the holder of at least a private pilot certificate issued under part 61 of this chapter who is the registered owner (including co-owners) of the affected aircraft and who holds a certificate of competency for the affected aircraft (1) issued by the holder of the production certificate for that primary category aircraft that has a special training program approved under § 21.24 of this subchapter; or (2) issued by another entity that has a course approved by the Administrator; and

(ii) The inspections and maintenance tasks are performed in accordance with instructions contained by the special inspection and preventive maintenance program approved as part of the aircraft's type design or supplemental type design.

(31) Removing and replacing self-contained, front instrument panel-mounted navigation and communication devices that employ tray-mounted connectors that connect the unit when the unit is installed into the instrument panel, (excluding automatic flight control systems, transponders, and microwave frequency distance measuring equipment (DME)). The approved unit must be designed to be readily and repeatedly removed and replaced, and pertinent instructions must be provided. Prior to the unit's intended use, and operational check must be performed in accordance with the applicable sections of part 91 of this chapter.

[M20C Driver]

Completely understand.  Context helps.  Unfortunately I do not have a zoomed out photo.  It is indeed the tailpipe joint.  The distant piece of scat was not the one with the bluish grayish exhaust spray evidence.  It was a piece more in the foreground (not pictured - the piece of scat that runs from the back of the dog house to the muffler shroud along the cowling support bracket.

Reading through Part 43 Appendix A it isn’t specifically listed so I guess it would require a pair of AP/IA eyes anyways.  There are a couple of things on the list that seem more involved than fixing this but I guess that is the problem with an inclusive list.  If it isn’t specifically listed…. 

[Ragsf15e]

6 minutes ago, M20C Driver said:

Completely understand.  Context helps.  Unfortunately I do not have a zoomed out photo.  It is indeed the tailpipe joint.  The distant piece of scat was not the one with the bluish grayish exhaust spray evidence.  It was a piece more in the foreground (not pictured - the piece of scat that runs from the back of the dog house to the muffler shroud along the cowling support bracket.

Reading through Part 43 Appendix A it isn’t specifically listed so I guess it would require a pair of AP/IA eyes anyways.  There are a couple of things on the list that seem more involved than fixing this but I guess that is the problem with an inclusive list.  If it isn’t specifically listed…. 

If it’s on the list, it’s clear, but if it’s not on the list is still might be considered “preventative maintenance”.  The list are examples and it isn’t exhaustive.  
 

Also, #30 may indeed allow you to disconnect an exhaust joint, lube it, reattach it.  That’s likely prescribed preventative maintenance.  I’m not competent enough to do that, but if you’re good at that, probably ok.  Might depend on your IA?

[Schllc]

Are you just looking at the blow by that is present on the spring?  There is nothing broken or askew in the picture so I’m assuming that is your reference  

if so, exhaust joints are all “loose”, I assume because of the movement of the metal under extreme heating and cooling, but blow by is inevitable. How much constitutes a problem is a good question.   It’s has been present around every turbo/wastegate/exhaust I have ever owned.  The NA engines I’ve owned  were better, but again my assumption was a function of low power production at altitude. 
how wrong/right I am will be evident shortly!

[M20C Driver]

10 minutes ago, Schllc said:

Are you just looking at the blow by that is present on the spring?  There is nothing broken or askew in the picture so I’m assuming that is your reference  

if so, exhaust joints are all “loose”, I assume because of the movement of the metal under extreme heating and cooling, but blow by is inevitable. How much constitutes a problem is a good question.   It’s has been present around every turbo/wastegate/exhaust I have ever owned.  The NA engines I’ve owned  were better, but again my assumption was a function of low power production at altitude. 
how wrong/right I am will be evident shortly!

Yeah, I noticed the blow by on the spring after I noticed a small amount of discoloration on the adjacent scat tube.  I can’t say as I have ever noticed blow by evidence in 16+ years of owning this C.  I know the springs allow the joint to move / expand / contract during vibration and thermal cycles but I assumed any visible blow by would require attention?  It could be coming from increased vibration from a broken tailpipe strap.  The tail pipe strap is what started this rabbit hole.  I have parts coming to perform SB M20-144.  Broken tailpipe strap is actually sugar coating the situation a bit.  The strap is completely missing.  It was there prior to a GI 275 EIS install and Annual but it is gone now.  The EIS was done by my trusted Avionics shop and the Annual was performed by my trusted AP/AI shop - neither of which have extra parts laying around.  Typically, I would think the springs break on the hanger strap assembly leaving the firewall attach point and tailpipe bracket securely in place.  I feel confident in saying someone removed it and forgot to put it back on.  I inquired about missing parts, but pointing fingers and throwing a fit would do no good as I have no idea who do it.  So I am moving forward. Checking for “tailpipe wiggle” is a part of every pre flight I perform.  It is still as tight as can be even without the strap so I didn’t know it was missing until now.  Perhaps the inflight vibration is allowing that blow by.

[47U]

12 hours ago, M20C Driver said:

I had the side cowl off to address my exhaust hangar

Rectifying your exhaust hanger issue will surely help stabilize the ball joint so that it doesn’t (or at least reduces) exhaust leakage.  Unfortunate that you came out of a mx activity minus the hanger.  As a long-time owner, you realize that the ball joint hardware, bolts and springs, require periodic replacement.  The heat takes a toll, and then there’s the ensuing corrosion/rust.  Replacing unserviceable exhaust joint hardware sounds a lot like preventative mx to me.  

I try to protect the ducts to the muffler shroud that are exposed to exhaust system heat with fire sleeve, I think Spruce sells it as protection for the fuel flow xducer in a 1 1/2” diameter.  I cut it open to make a flat sheet and secure it to the duct with safety wire.  Zip ties generally won’t take the heat (as I learned).  I replaced my exhaust with a Knisley PMA (slip joint risers) a few years ago.  Changes to the orientations of the duct connections on the shroud were required because the tailpipe outlet on the muffler was changed.  Routing the ducts became problematic and a work in progress… as the pic suggests.  This was not the final solution.

 

[Schllc]

Sounds like you have answered your own question….

cant you just make the back half of the bracket?   I mean an owner supplied, even if inferior, seems a better alternative to nothing. 

[Yetti]

The most common method for the tailpipe strap is to cut the sidewall out of an old tire.     A good sharp Stanley utility knife is your friend here.

[MikeOH]

2 hours ago, Ragsf15e said:

If it’s on the list, it’s clear, but if it’s not on the list is still might be considered “preventative maintenance”.  The list are examples and it isn’t exhaustive

@Ragsf15e is alluding to the COLEAL LOI, which I've attached.  The relevant/salient excerpt:

 

Coleal-Bombardier Learjet_2009_Legal_Interpretation.pdf

[PT20J]

1 hour ago, M20C Driver said:

Checking for “tailpipe wiggle” is a part of every pre flight I perform.  It is still as tight as can be even without the strap so I didn’t know it was missing until now.

This may be part of your problem. There should be movement of the ball joint, especially without the tailpipe attach hardware.

If this were my airplane, I would remove the tailpipe, inspect it for any damage and clean the ball mating area with Scotch-Brite. I would coat the mating surface of the ball with a light coat of C5-A anti-seize and reassemble it with the correct tailpipe hardware.

[M20C Driver]

2 hours ago, MikeOH said:

@Ragsf15e is alluding to the COLEAL LOI, which I've attached.  The relevant/salient excerpt:

 

Coleal-Bombardier Learjet_2009_Legal_Interpretation.pdf 649 kB · 0 downloads

I have not previously seen this.  Thanks for sharing.

[M20C Driver]

3 hours ago, Schllc said:

Sounds like you have answered your own question….

cant you just make the back half of the bracket?   I mean an owner supplied, even if inferior, seems a better alternative to nothing. 

Thanks to Shadrach I was actually able to source a bracket on EBay.  It is enroute.  Not cheap but what on an airplane is?!?!  The SB kit# 1 for the C model contains most of the needed new hardware firewall downward.  It does however require reusing the bottom bracket which I did not have.  Thankfully I was able to get one.  Owner produced would have been next on my list of options.

 

[M20C Driver]

1 hour ago, PT20J said:

This may be part of your problem. There should be movement of the ball joint, especially without the tailpipe attach hardware.

If this were my airplane, I would remove the tailpipe, inspect it for any damage and clean the ball mating area with Scotch-Brite. I would coat the mating surface of the ball with a light coat of C5-A anti-seize and reassemble it with the correct tailpipe hardware.

I think this sounds like a great plan to me with the addition of installing the new SB M20-144 exhaust hanger kit at the same time.  Then reevaluate where I am at.  Thanks for the help Skip.

[Yetti]

On 12/24/2025 at 11:56 AM, MikeOH said:

@Ragsf15e is alluding to the COLEAL LOI, which I've attached.  The relevant/salient excerpt:

 

Coleal-Bombardier Learjet_2009_Legal_Interpretation.pdf 649 kB · 0 downloads

Changing a tire is on the PM list.   Removing and install a brake caliper is not on the PM list.    But you can't change the tire without removing the brake caliper.    

[Skates97]

On 12/24/2025 at 7:26 AM, M20C Driver said:

Completely understand.  Context helps.  Unfortunately I do not have a zoomed out photo.  It is indeed the tailpipe joint.  The distant piece of scat was not the one with the bluish grayish exhaust spray evidence.  It was a piece more in the foreground (not pictured - the piece of scat that runs from the back of the dog house to the muffler shroud along the cowling support bracket.

Reading through Part 43 Appendix A it isn’t specifically listed so I guess it would require a pair of AP/IA eyes anyways.  There are a couple of things on the list that seem more involved than fixing this but I guess that is the problem with an inclusive list.  If it isn’t specifically listed…. 

A good relationship with you AP/IA is invaluable. There are a number of things that I have texted mine to ask if he was okay with me taking care of. Sometimes it's "Yes, go ahead," and others it is "Sure, but let me see it when you're done and get a logbook entry for you."

[Bartman]

7 minutes ago, Skates97 said:

A good relationship with you AP/IA is invaluable. There are a number of things that I have texted mine to ask if he was okay with me taking care of. Sometimes it's "Yes, go ahead," and others it is "Sure, but let me see it when you're done and get a logbook entry for you."

Exactly. 

Over time my IA has given me increasing responsibility. This is based on how I research and diagnose, present my facts and plan, and largely based on what I have learned here on Mooneyspace from many more knowledgeable than me.  He sees my performance on multiple complicated repairs and I encourage a second set of eyes, but he knows I won’t declare it’s done until it is done right.  I have enjoyed this journey very much.