1974 M20F Exhaust Failure

[AlbertF]

This just happened at the end of a local flight.  #3 cylinder exhaust pipe broke at engine and fell apart inside cowl.  I havent talked to my mechanic about it yet (just found it today...Sunday), but wanted to get some initial thoughts from the experienced.

1.  Top Pipe:  Does this require a new exhaust pipe or can a new flange be welded?  If it failed once, first thought is better new.  Any thoughts on where to buy a new pipe?  I'm a fan of quality parts with non-dealer prices.

2. Muffler:  The pipe that comes out of the muffler that connects to this pipe now rotates freely at the muffler (yellow circle).   Is it supposed to rotate or is it broken at the muffler as well?  Again, is this a part that can be repaired with welding?   I suppose I would need an entire new muffler if the #3 cylinder pipe connection is supposed to be welded and cant be repaired.

3.  Thoughts on welding (if possible) versus replacing new?  If I did need to replace muffler, any experience on quality parts and good prices new or used?

Thanks, Albert

[Ron McBride]

Have Dawley rebuild your system. 

[skykrawler]

Your stack and muffler both need to be 'rebuilt' or replaced.   Inspect the other three very carefully.  Go with the no-blow gaskets.

[EricJ]

The downpipe is probably best to just get a replacement.   The pipe into the muffler may be repairable.   Ask around for welding/fabrication shops that the local A&P/IAs use or trust and send the muffler there, in coordination with your A&P/IA.    They will probably replace that length of pipe and will need to know how it should be oriented in the muffler.

[AlbertF]

So send the muffler (and broken exhaust pipe) to Dawley and they'll repair and return.  I'm not familiar with Dawley, but I'm assuming they are at the top of your list.  I'll look them up and hopefully my mechanic has the same suggestion.  Thank you.

[RLCarter]

When you go back together loosen ALL flanges, clamps and joints, snug evenly in stages to keep things “RELAXED” and use “Mouse Milk” on all the joints.

[Guest]

The pipe that goes into the muffler should have a flame tube inside the muffler.  The fact that the pipe turns freely suggests that the flame tube is gone as well.  Rebuild or replacement is in order.

Neither of these failures happened over night, lack of maintenance and proper inspection come to mind.  We pressure check the exhaust system with an old shop vacuum at every Annual Inspection as well as thorough visual inspection.

Clarence

[carusoam]

great pics, Albert!
 

+1 for many signs appear prior to falling apart...

Look for exhaust stains... so you recognize them the next time...

Check your CO monitor to see if it was talking to you...

The heat muff tries to poison you with CO in a similar fashion...

So... when you get all the parts to re-assemble... make sure your mechanic has the procedures to follow...

Avoid adding stress when connecting everything back together...

PP thoughts only, not a mechanic...

Best regards,

-a-

[jetdriven]

all that tan fin and spark plug staining tells the tale its been leaking for a while. Get used to what that looks like, so you can recognize it next time.

[hammdo]

4 hours ago, Ron McBride said:

Have Dawley rebuild your system. 

Ditto, that is the way to go. They did my B and my C.

Here is mine (C) before and after (yep, overhauled and not new):

-Don

 

 

~$850 for mine - (plus shipping/labor). Depends on condition of exhaust. YMMV...

-Don

[Mooney217RN]

From my personal experience with a 1974 E Model which I owned/flew for 18+ years; replace the entire system with a PowerFlow Exhaust.  You'll never be happier about an engine mod decision.  Your engine will run smoother, you'll increase your manifold pressure, and it the performance is very noticeable at altitude.  PowerFlow claims 10% increase in HP.  I'd believe it.  You'll find that it's probably on par with repairing your exhaust system as opposed to replacing it.

However, if you need a new exhaust and don't want to spend the $$$, I have the entire exhaust system off a J model sitting in my hangar.

[AlbertF]

Thanks all.  Good comments to help inform my discussion with my mechanic.

[LunkenPilot]

I also just made the decision to put on a Powerflow. The old exhaust was looking weak, and I have heard good things about the improved performance. But I won’t know for sure until the end of the month!

[Mooney217RN]

On 1/4/2021 at 3:46 PM, LunkenPilot said:

I also just made the decision to put on a Powerflow. The old exhaust was looking weak, and I have heard good things about the improved performance. But I won’t know for sure until the end of the month!

I replaced mine on my E Model when I kept repairing the exhaust.  On one more exhaust crack, I said the heck with it, and purchased the Power Flow system.  it worked great, and their support is fantastic.

[Tcraft938]

First, bummer that happened, a real pain in the seat and fortunate you didn't get CO poisoning.  Last week for my oil change, my A&P/IA had me do 99% of "since you can legally do this and you have all that cowl off, let me show you things to inspect and how to do it so you can potentially be aware of a minor problem before it becomes a huge one".  Exhaust was the first thing and spent a lot of time on it.  Apparently in November he had someone have an issue similar to yours, they didn't look inside, left him a text message "plane seems louder and making a banging/rattle sound" and they took off for a 45 minute flight to him (new customer to him had the pre-buy done in another State).  The pilot and wife got there and were feeling quite ill.  He said as they taxied in the tailpipe was hanging down way lower than normal and banging the heck out of the cowl flap.  That's when he felt sick to based on what could have happened.  I'm sure once feeling better they received a discussion in, "if it's rattling banging or not right, call me, I'll come look at it, DON"T fly it to me!!"   As for mine, the exhaust was fine, an oil line received some additional support to prevent potential chaffing, carb heat adjustment and cowl flap cable needs replaced this weekend along with some minor doghouse TLC (more learning for me) which was perfect example of catching a little thing early that would be major 5 months and 50 hours into the future.  

[AlbertF]

Just to keep everyone up to date, we removed the exhaust and sent it off to Dawley.  Our mechanic looked at the damage and surmised the #3 pipe broke at the muffler first and after several hours of stress and vibration, finally broke at the cylinder flange.  Hopefully Dawley can simply weld it all back together.

[jetdriven]

Usually not that easy. They measure the pipe wall thickness and its below spec. then everything has to get "overhauled" which means cut the pipe off at the flange, and replace that. Then replace the flange.

[carusoam]

The good news...

If it needs to be OH’d...

It magically comes back looking brand new...

Depending on how many hours it has accumulated... the pipe parts nearest the exhaust valves get awfully thin via erosion...

NA engines typically have decades and thousands of hours on the exhaust system...

TC’d engines are much tougher on their exhausts, as the pipes are kept much hotter until they reach the TC...

The why... Rapid expansion of exhaust gas, has a very strong cooling affect... the EGT drops significantly over the distance...  

The exhaust pressure doesn’t drop, until after the TC...

The average hottest part of the exhaust is usually where multiple streams of exhausts come together... hence the reason to measure the TIT... that is the hottest point (on average)...

Why the average... waves of heat come through the pipes.... with every plug firing exhaust stroke... so there is a lot of time before the next heat wave comes through...   (our plugs fire twice every two revolutions, but only one has any fuel to be burned in the cylinders... this is known as a wasted spark... the mags have no idea when the fuel gets added...)

The magic of the four stroke aviation engine...   

PP thoughts only, stuff I remember from somewhere...

Best regards,

-a-

[MikeOH]

Another happy PowerFlow customer.

[cliffy]

What about the LUBE requirement every year on the Power Flow?

[MikeOH]

17 minutes ago, cliffy said:

What about the LUBE requirement every year on the Power Flow?

What about oil and filter changes, lubing the Heim joints, zerks, etc....it's just not that big of a deal.

[cliffy]

Didn't mean to infer that it was a problem just something to take into account if a PF is put on.

It gets missed a lot.

[MikeOH]

21 minutes ago, cliffy said:

Didn't mean to infer that it was a problem just something to take into account if a PF is put on.

It gets missed a lot.

Good point!

I always point out the ICA for just that reason.

[Guest]

My wife called Dawley today about a P210, apparently they are closing the business and retiring.

Clarence

[cliffy]

Another nail on the coffin of GA