Sealing the slip fit exhaust joint?

[flyingchump]

So I have a very slight CO concern I want to solve.  While in cruze my new sensorcon CO detector reads about 2-3 ppm.  During take off it's a bit higher.  

-doesn't change when the heater is on or off.

-doesn't change with the vents on or off.

-i recently resealed the door

-i recently sealed some old unused holes in the firewall...

My most educated guess is that the exhaust slip joint is leaking gasses.  There are some deposits on the pipe.  I recently purchased new nuts to replace the old ones in the photo and I tightened as mush as I felt comfortable but I was getting nervous about stripping the nut.  It looks like it's still leaking to me.  It there some tribal knowledge to seal this thing?

[EricJ]

The slip joints are pretty reliable, as they swell under heat and seal up.    It is much more likely that it is coming in through the floor or the tail around the baggage area or some other area like that.

That said, 2-3 ppm is nearly zero as far as CO measurements go.    Many of us routinely see numbers far higher than that.   Whatever leak you have, it is very small and not at all unusual.   

 

 

[PT20J]

Double check the door. On my J I had to do it twice because the fit between the door and the fuselage is so variable. 

[Shiny moose]

I would also say the door seal, wing/ fuselage duct tape under fairing, baggage door seal last, probably not the slip joints. 

[GeeBee]

2-3 ppm is minimal in most vehicles. I can get 2-3ppm in heavy traffic in my car.

 

 

[philiplane]

What pipe is that Autozone clamp on?  It can't slip if it's clamped, and the forces will transfer to other parts of the system, where it will break. And then you'll have a huge leak, and possibly a fire. I would remove the clamp, and oil the joint, although the pipes are probably already deformed.

FWIW, the threshold for aviation CO warnings is 40 PPM. The detectors sold for home use are for low airflow environments where lower readings are important. 3 PPM can slowly build up in a house because it's not moving at 130 MPH. Airplanes are flying wind tunnels where 2-3 PPM just blows through on the way out the tail. It can't build up to dangerous levels. 

[PT20J]

That joint isn’t actually a slip joint because of the clamp. It’s for adjustment at installation. The slip joint on that header is closer to the muffler. The slip joints are supposed to be lubricated with C5-A when assembled. 

Skip

Edited May 23, 2021 by PT20J
Added picture

[philiplane]

28 minutes ago, PT20J said:

That joint isn’t actually a slip joint because of the clamp. It’s for adjustment at installation. The slip joint on that header is closer to the muffler. The slip joints are supposed to be lubricated with C5-A when assembled. 

Skip

the OP's ID lists an M20E, which doesn't have that joint. Good thing

[PT20J]

8 minutes ago, philiplane said:

the OP's ID lists an M20E, which doesn't have that joint. Good thing

I missed that. Thanks for the clarification. 

[philiplane]

I've seen people put clamps on the muffler-to-riser slip joint. Then the riser breaks off at the base of the exhaust port with bad consequences.

[Yetti]

Just mouse milk the slip joints any time the cowl comes off.   Have you replaced all the duct tape in the cabin with alum tape?   About a weekend job.

[flyingchump]

6 hours ago, philiplane said:

the OP's ID lists an M20E, which doesn't have that joint. Good thing

Yea, I do have a slip joint. 

I was surprised when I referenced the parts manual and no slip-fit was identified.  At some point in this planes history, someone must have made a change to the existing exhaust or replaced the exhaust with one from a later model.  I'll have to check the log books when I have some time.

 

[Guest]

Some sort of field approval or STC to install a J model exhaust on an E model.

Strangely the new replacement clamp is a standard muffler clamp in a Mooney box.

Clarence

[PT20J]

Hey, I’m not arguing with anyone because most of you know a lot more than I do. I just try to look this stuff up to learn more. But, according to this source, there are two different muffler systems for the M20E — ribbed and studded. The ribbed is like the M20J and has a clamp on the header for cyl 4. The studded does not.

Skip

 

[1980Mooney]

I am with Skip.  Most of you seem to know more but a lot can be resolved just by looking at the Mooney Parts Manual.  You have a 1966 E and I assume you have a manual.  But if not I have attached one.  Apparently Mooney built all those models with either a Hanlon and Wilson studded core muffler or with a Mooney manufactured ribbed core muffler.  See pages 142 - 144C.

1965-67 Mooney-M20C,D,E,F-parts-manual-Rev. July 1976-pdf-free.pdf

[1980Mooney]

The Hanlon and Wilson studded muffler had spring compression ball joints and no U clamp.  If you dig into the remarks it appears it was installed in each of the C,D,E and F models.

The Mooney built ribbed muffler came with slip joints.  The notes indicate that it appears it was installed in each of the C,D,E and F models also. The first ones also had ball joints on stacks 2 and 4.  The later ones did away with the ball joints and apparently added the joint with the U clamp.  The foot notes on page 144C says that the Mooney built ball joint cores were no longer available and to replace with newer design.

The drawing is really poor and does not show the clamp.  But if you go to the parts list it shows your clamp on stack 4.

Here is another supplier that clearly shows the clamp.

 

And that is not an "Autozone clamp" as someone called it.  That is a $218 clamp from Lasar if you can get it.  You may not be able to read the dark print that says "SOLD OUT".  

 

Don't over torque it and strip the threads!

Edited May 1, 2023 by 1980Mooney

[Guest]

Many of us volunteer our efforts here helping our fellow owners.  If someone wants to pay me for my efforts to look up parts I’ll put in more effort and try to be more accurate.

Clarence

[PT20J]

2 hours ago, M20Doc said:

Many of us volunteer our efforts here helping our fellow owners.  If someone wants to pay me for my efforts to look up parts I’ll put in more effort and try to be more accurate.

Clarence

Well, I think you are pretty accurate as it is and I think most of us appreciate your fact-based posts and you freely sharing knowledge that can only be gained from years of experience maintaining these airplanes. I know I’ve learned a lot from reading your posts. 

Thanks,

Skip

[EricJ]

5 hours ago, M20Doc said:

Many of us volunteer our efforts here helping our fellow owners.  If someone wants to pay me for my efforts to look up parts I’ll put in more effort and try to be more accurate.

Clarence

You usually go way above and beyond in posting the relevant IPC pics, etc.    I think it's appreciated!   I've always thought it was pretty impressive, anyway. 

[Sixstring2k]

12 hours ago, M20Doc said:

Many of us volunteer our efforts here helping our fellow owners.  If someone wants to pay me for my efforts to look up parts I’ll put in more effort and try to be more accurate.

Clarence

Learned much from you and many other insights into this planes, Very appreciated. 

[Raptor05121]

Amazing post. Good to hear such a free-flow of information. Unlike that $250 pipe clamp. Aviation prices never cease to amaze me

[flyingchump]

Reporting back.

Since I could find no record of the last time someone actually took the whole exhaust off the plane.  I did.  Here is what I found:

-All 4 of the flanges that bolt to the head were a smidge off from being flat.  They were filed mostly flat before installation.  The rest of the exhaust was inspected and found in good condition.

-While the exhausted was off, I took the opportunity to change out the orange intake orings on the intake tubes.  They cant be removed with the exhaust on.  2 of them looked great (but not round anymore) and the other 2 had some small cuts and scars.  Nothing major and I don't think they were leaking much, if any, but still...

-The paper intake gaskets were gooped up with Permatex (for the first time ever) and installed.  One intake tube was not quite flush with the head so that was corrected.  Now I'm confident that I do not have any more induction leaks!

-Again while the exhaust was off, the sniffle valve was removed, cleaned, and reinstalled.

-Exhaust was reinstalled with new gaskets and c5-a on the 2 slip joints for the lower riser on #4.

-Assemble cowls, what for the next day so the Permatex cures, and test run.

Upon starting the next day, the idle was roughly 200-250 RPM higher.  Previously the plane idled at 650-700 depending on a few things.  But now it idled at 900-1000.  Nothing pertaining to the throttle or mixture were changed.  

I most note that there was considerably less vibration while on the ground.  I think cylinder #2 was the biggest intake leak and causing the engine to run rough on the ground at least.

Could sealing up all the intake tubes and exhaust flanges change my idle?  Should I adjust the idle screw on the servo now that the intake and exhaust are solid, or might there be something else going on?

[EricJ]

Usually an intake leak causes an increase in idle RPM, not a decrease.    You may have introduced a leak, which is not unusual.   Double check the seating and fastener torques on the intake tubes.

 

[Guest]

I’m with Eric, an induction leak would/should cause a rise in idle RPM.  If they’re all sealed now the idle RPM should have dropped.  Make sure that the flange on the tube is centered in the recess in the aluminum flange.

Also the Continental version of the Lycoming intake gasket is made of a slightly thicker material and takes up irregularities.

Clarence

[flyingchump]

On 6/6/2021 at 7:05 PM, EricJ said:

Usually an intake leak causes an increase in idle RPM, not a decrease.    You may have introduced a leak, which is not unusual.   Double check the seating and fastener torques on the intake tubes.

 

Well you guys were spot on again!  I looked around my intake tubes multiple times and didn't see anything wrong but then a small shadow caught my eye...  One of the intake orings was out of its seat and causing an intake leak.  My guess is that the intake tube was pushed too far into the casting and part of the oring got snagged on a sharp spot starting a tear.  After I removed the intake tube the oring was completely torn through.  If I continued to fly like this I think my problem would have gotten progressively worse as the oring would have split in place.

I replaced the oring and the engine runs much better now.  After a ground run and test flight, the oring is where its supposed to be and the idle is back to normal.