Mufflers, BE CAREFUL

Mods, approval, 337's, STC's, fun with the Feds.
User avatar
freedom
100+ Posts
Posts: 239
Joined: Fri Jul 17, 2015 6:34 am
Contact:

Re: Mufflers, BE CAREFUL

Post by freedom »

bit off topics, but how loose is rightly loose on the exhaust pipes?

User avatar
maules.com
100+ Posts
Posts: 3144
Joined: Tue Aug 29, 2006 4:01 pm
Contact:

Re: Mufflers, BE CAREFUL

Post by maules.com »

Set the header to muffler pipes bolts so that after tightened, you can put a wrench on bolt(not nut) and move it with a crooked finger on a 3" wrench.
Set the tailpipe clamp so that it does not rattle but you can move the aft end of the tailpipe over 2" in any direction
Jeremy
www.maules.com
Maule AK Worldwide

User avatar
drak130
100+ Posts
Posts: 169
Joined: Mon Oct 21, 2019 7:59 am
Location: Angier, NC
Contact:

Re: Mufflers, BE CAREFUL

Post by drak130 »

All,

So based on remarks regarding the Maule mufflers, I decided to inspect the muffler myself instead of waiting until the March annual I have scheduled at Maule.

Ordered new clamps and soaked the old bolts in KROL for a couple of days. That worked on all but one bolt (of course, it is always just one bolt or nut) so hacksawed that one off. Took the heat muff off and as Andy predicted have one that is starting to crack at the bend on the inboard side. Clamps on the way.

Did an eyeball inspection with a flashlight and borescope of both mufflers. They look good with no cracks, but there is nothing in there. No cones, baffles, screens or anything else. Looked like the inside of a coffee can (minus the coffee). Am I missing something?

Also, as I put things together, any advantage to using nickel anti-seize on the bolts? Good to 2400 degrees F.

Thanks and Cheers
Tim

User avatar
Lmjr
Posts: 20
Joined: Sat May 18, 2019 8:03 am
Location: Anchorage
Contact:

Re: Mufflers, BE CAREFUL

Post by Lmjr »

Below is a picture of a failed flame tube inside my Maule muffler. This picture is taken looking up the muffler exhaust port. It should not just be an empty muffler can!

I replaced mine with a set of Atlee Dodge mufflers, IMHO much better setup.


Image

User avatar
andy
Site Admin
Posts: 1662
Joined: Mon Aug 06, 2007 2:05 pm
Location: Lake James, NC, USA
Contact:

Re: Mufflers, BE CAREFUL

Post by andy »

The flame tube is inside the pipe. Outside the pipe are standoffs that support the outer shroud. The outer shroud is relatively thin. The bent edge of the outer shroud where it is screwed to the other edge is where the cracking usually occurs. You can use safety wire or a 6" (if I recall correctly) stainless steel hose clamp to reduce the stress and vibration that causes the cracking. I like the hose clamp better. The flame tube is spot welded to the inside of the pipe. Vibration can cause the welds to crack or the flame tube can disintegrate due to heat and combustion byproducts. It's dangerous to operate without the flame tubes. Flames may come out of your tail pipe.

Unfortunately for us 4-cylinder owners, Atlee Dodge only offers 6-cylinder Maule exhaust systems. Acorn Welding offers 4 and 6 cylinder Maule exhaust systems but I don't know how they compare to the stock Maule versions. Dawley Aviation rebuilt my exhaust system in 2019 and did a good job although shipping wasn't cheap.

You will almost certainly have to ship your old exhaust system to have it repaired or replaced. Each airplane is individual in the angles of the welds and pipes in the exhaust system. Even if you buy a new system from Maule, like I did in 2005, it may not fit your airplane at the headers or tail pipe hanger strap.
Andy
1986 MX7-180
Image

User avatar
drak130
100+ Posts
Posts: 169
Joined: Mon Oct 21, 2019 7:59 am
Location: Angier, NC
Contact:

Re: Mufflers, BE CAREFUL

Post by drak130 »

Experts,

Took a couple pictures today before leaving town. Included exterior pictures without the heating muff.

To me the muffler appears to be in good condition especially considering 700 hrs (nothing in the logbook regarding replacement). Again, just looks like an empty can to me with an inlet in the front for the first cylinder and then two other short stacks in the top for the other two cylinders.

Ruling?

Thanks Tim
Image

Image

Image

User avatar
Mog
100+ Posts
Posts: 973
Joined: Fri Nov 26, 2010 8:01 pm
Location: Dallas, TX
Contact:

Re: Mufflers, BE CAREFUL

Post by Mog »

Ruling is your flame tube or Spark arrestor is gone. You can see the end of it in the tube. It’s the perforated part.

Now, until proven otherwise I’m in the “prove its purpose is anything but a spark arrestor”. Because I am now finding tons of people without them at all. AND, if you look how the right side exhaust is done (at least on the franklin), the flame tube does not actually interact with any of the direct heat/exhaust from any of the three cylinders. This is because the flame tube is not long enough. I now believe that anyone with a hole in their exhaust has been running too hot of EGT’s or their is something fundamentally wrong with their setup.

Again, I’m open to someone proving me wrong, but this stuff just isn’t adding up now.

User avatar
maules.com
100+ Posts
Posts: 3144
Joined: Tue Aug 29, 2006 4:01 pm
Contact:

Re: Mufflers, BE CAREFUL

Post by maules.com »

The pictures show baffle/tube is burned away, leaving the end 2" tack welded in the tailpipe attach tube.
Grind out the tack welds, remove the 2" section, replace with new baffle from Maule and tack weld in place.
The baffle will reach to almost halfway across outlet from #3 rightside or #4 leftside.
The exhaust flow from #s 1 and2 interferes with flow from #s 3 and 4 which helps prevent overheating forward end of muffler can.
However, if baffle is missing, #s 5 and 6 dump directly onto rear end of muffler can which eventually crystalizes the metal can at bottom rear and a backfire can and will blow a hole in it.
It is important when doing muffler inspections to remove the heat shield to not only look for cracks at the standoff welds but for swelling of the muffler at lower right of can.
Jeremy
www.maules.com
Maule AK Worldwide

User avatar
drak130
100+ Posts
Posts: 169
Joined: Mon Oct 21, 2019 7:59 am
Location: Angier, NC
Contact:

Re: Mufflers, BE CAREFUL

Post by drak130 »

Many Thanks Ya'll,

Just got off the phone with Maule and at $98 a piece sounds like (airplane) cheap insurance. Thanks for the input/education. I did take the jackets off and gave everything the once over. All looked good except for the missing pieces and a small crack in one shroud at the retention bend over. Clamps on the way.

Cheers
Tim

User avatar
Mog
100+ Posts
Posts: 973
Joined: Fri Nov 26, 2010 8:01 pm
Location: Dallas, TX
Contact:

Re: Mufflers, BE CAREFUL

Post by Mog »

I did a bit of a write up on another thread on what you need to do to replace the tubes. It’s not that difficult but it’s a bit of a pain.

User avatar
drak130
100+ Posts
Posts: 169
Joined: Mon Oct 21, 2019 7:59 am
Location: Angier, NC
Contact:

Re: Mufflers, BE CAREFUL

Post by drak130 »

Hello all,

Got the flame tubes from Maule. Look great! FWIW, they still make their exhaust systems in house but due to raw material issues they are on a 22 week backlog. So much for new right now. Dawley says they can install the flame tubes or rebuild the whole system for $900 but either way it will be a 30-45 day turnaround.

My current A&P is a great guy but does not due TIG welding. No other A&Ps near me do TIG either. Found a local professional welder that has been doing TIG and MIG for 35 years that will do the job next week but he is not an A&P (he does custom fabrication for local businesses and repair work at the nuclear power plant)

Choices are:

1-Fly the plane sans flame tubes until the March annual at Maule and hope that I don't burn through the cans (plan on inspecting every 25 hrs) and they can fix or overhaul

2-Send system to Dawley and have them IRAN system and eat the down time and coin

3-Have my A&P effect the repair with a brand new TIG welder with no experience

4-Have the professional welder tack in the cones. I would have to remove and replace the exhust myself which I am completely comfortable with. Ordered all the appropriate parts plus a few "just in case" pieces and have consolted the lycoming parts and shop manual.

My vote is for option 4 but don't want to get sideways with the FAA or my A&P (who I plan on talking to tomorrow about what he is and is not comfortable with)

I have looked at FAR 43 Appendix A and as a crap house lawyer would consider this preventative maintenance using "non complex" procedures.

I realize i am opening myself up to criticism but honestly want honest opinions to help shape my knowledge. I have owned aircraft before but it seemed easier 20 years ago and this new landscape of aircraft maintenance seems bizarre and contrictory at tmes. For me down time is more a factor than money but at of the end of day I want a safe aircraft I can fly my family to the mountains of NC in.

Thankfully
Tim

User avatar
Andy Young
100+ Posts
Posts: 1545
Joined: Wed Oct 05, 2011 7:10 am
Location: Alaska, Antarctica, Colorado, and Others
Contact:

Re: Mufflers, BE CAREFUL

Post by Andy Young »

I’d also be inclined to go option 4. Legally speaking, your A&P needs to sign off on your removal and reinstall work. He or she can (and legally must) also inspect and sign off on the welding work. Welder doesn’t have to be an A&P, as long as an A&P approves the work the welder does. I use a local non-aviation welder all the time, and sign off his work.

User avatar
Mog
100+ Posts
Posts: 973
Joined: Fri Nov 26, 2010 8:01 pm
Location: Dallas, TX
Contact:

Re: Mufflers, BE CAREFUL

Post by Mog »

Other options to tag along with #4.

You can mig weld the tubes in. In fact I would recommend this because trying to tack inside the tube with a Tig torch is a bit of a pain. Any decent welder worth his pay will be using gold gas or 25% argon. This is fine if you have stainless wire. There is nothing to purge so this is all very simple and easy welding. The final option is to weld with a mig machine with regular steel wire. The weld in this case will not be protected by the stainless qualities but it will be fine as it’s covered in soot anyways. The reality is that you are just racking this part in place. It’s not structural in any meaningful way. Just make sure it won’t vibrate itself to death. I recommend alternating your tacks from the end of the tube to the back at 45°. This will brace the pipe well and keep it from vibrating a lot.

PS, I know now several people that have mig welded theirs in with regular wire and it has held for many years and hours.

Your biggest issue will be getting the new tubes into the exhaust, the welding becomes trivial after that.

Post Reply

Who is online

Users browsing this forum: No registered users and 14 guests