UPDATE: Another cracked exhaust. 2002 MXT7-180A. 1150 hours

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Mountain Doctor
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UPDATE: Another cracked exhaust. 2002 MXT7-180A. 1150 hours

Post by Mountain Doctor »

Now it's the pilot side. The crack is at what I'll call the rear bulkhead of the muffler, outside of the shroud. Not enough to leave any grey lead deposits or marks on anything, but will need to be fixed.

Multiple calls and messages to Maule asking about a new replacement price have not been returned.

Should I pull and get this one rebuilt? Continue to try to fine a new one? There is a used one on eBay but I don't know if that's better or worse than what I have already.

I assume having it welded by a local welder is verboten...
Last edited by Mountain Doctor on Mon Jun 08, 2020 10:51 am, edited 1 time in total.
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Andy Young
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Post by Andy Young »

It’s fine to use a local welder , as long as your A&P is comfortable signing off the repair.

If you decide to replace, I highly recommend the Atlee Dodge mufflers. Better alloy, thicker material.

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maules.com
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Post by maules.com »

Cracks in 'rear bulkhead' are most often attributed to a too tight tailpipe clamp.
The tailpipe is long and its attached to firewall via hangar but muffler is attached to the engine which rotates on its mounts, especially the O360 at startup and shutdown, so there must be enough "give" at tailpipe/muffler joint to allow plenty of movement. That is 2-3" in all directions when hangar is released.
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Post by Mountain Doctor »

Thanks guys.

I'm cognizant of keeping the tailpipes loose and have done that since the plane was about new. Still crack. I'm careful on minimizing vibration and eliminating backfire by carefully retarding the throttle and I've had the rotating mass dynamically balanced when the plane was new but this still happens. I think its a design flaw somewhere.
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Post by Mountain Doctor »

I'm looking into a local welder.
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Maule988ms
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Post by Maule988ms »

Pulled the trigger this year and had atlee build me some new ones. They are sooooo much better than the originals. This will be the 4th set of mufflers since it was new. I have to believe these are gonna hold up better than the maule version

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Post by VA Maule »

Going forward don't neglect to losen the muffler from the cylinder stubs and clean these 4 joints whenever you take the bottom cowling off. In fact if you seep it several times before hand with Hopps #9 ( day and evening before works best if you have the time) most of the crud will wipe off with a little green scotch bright. Upon reassembling a heavy coating of nickel antiseze keeps the new crud from gripping too tight.

When I got mine some years ago with a little more than 200hr total time since new very first annual rear of both mufflers were cracked in several places each at the exit end. Neither muffler or tail pipe were drilled for the dowel that's welded to the clamp. Clamp was just wrenched down good"N"tight no wiggle or jiggle at all, rigid as could be. Being handy with a welder and somewhat experienced with heavy equipment and what it takes to keep that stuff from destroying itself from vibration and shock loads, with the blessing of an understanding and cooperative IA . I welded up the cracks and added what I'd call reinforcing bridge welds( 3-4 passes on top of each other to create like the web section of an I beam) to the rear of each muffler can ( looking at the rear of the can they look like a cross between a bullseye and a spider web) . Going on 12 years and 1600hr total time now and NO MORE CRACKING.
I believe that the longevity of mine has been a combination of the initial repair I made with the blessing of an understanding IA and the extra 1/2 hour I add to an oil change by cleaning the joints in the system.
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Post by Mountain Doctor »

Maule988ms wrote:Pulled the trigger this year and had atlee build me some new ones. They are sooooo much better than the originals. This will be the 4th set of mufflers since it was new. I have to believe these are gonna hold up better than the maule version
I'd go with them but they don't have a muffler STC for my plane.
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UPDATE:

Post by Mountain Doctor »

UPDATE:

I removed the muffler to inspect it closer and there is no crack. The leak was from the clamp between the muffler and the tailpipe. There is a locating hole drilled through both and a pin from the clamp fits through the holes. That's where the air was escaping. I also inspected the flame tube and it was fine. I put it back on and will consider it good.

So, no new muffler at the movement is a relief and thanks to all who replied.

I added this update as it may help someone else out down the road.
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Post by Mountain Doctor »

Quick question...

I know the joint between the muffler and tailpipe is supposed to be loose but how do you leave the clamp loose and the nuts don't fall off? Double nut it?

Also if it's loose it will obviously leak. I assume the CO will just spill overboard in the cooling air and not bother anything or anyone?
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Post by bobguhr »

Mr Mtn. Doc,
Maule puts a Pal Nut on top of the U Bolt fastening nut to act as a jam nut. https://www.aircraftspruce.com/catalog/ ... alnuts.php. I've yet to lose one, you can just about hand wiggle the u-bolt on my exhaust. If you over tighten the u bolt nuts, besides the cracking, you will have a hell of a time separating the tailpipe from the muffler during the annual flame tube inspection. I've never had an exhaust gas intrusion into the cabin issue, the muffler outlet slides into the tailpipe outlet, I'm guessing that mitigates the leakage. The locating hole leakage hasn't been an issue for me. Disclaimer: advice here is free and just my experience. YMMV

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Post by Mountain Doctor »

Thank you. Exactly what I needed to know. Now I just hope I can reach up from underneath without having to remove the lower cowling again. that's a pain. :D
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Re: UPDATE: Another cracked exhaust. 2002 MXT7-180A. 1150 hours

Post by bobguhr »

Belated photo of the exhaust clamp install

Image

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