FYI,  UL mufflers (at least for the 350iS) now come from the factory with a reinforcing gusset to the exhaust pipe flange.  I repaired my original (which had cracked), but ordered a new one in the event of future cracking/needed replacement.  Likely was a identified issue...

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On my Jab 3300's muffler, the exhaust pipe goes completely through the muffler and exits the opposite side and that is capped shut.  I haven't heard of many, if any, cracking problems with this design, which has been around for decades.  Sounds like UL is doing something similar now and I'll bet it'll be much more durable.



How should the Exhaust pipe be installed?  Long or short end of the "dogleg" pipe in the muffler? The other end pointed at the ground or to the rear of the Airplane?  I have seen pics of both...

Scott, I went short end into the muffler flange then rotated the long end until it looked the way I wanted it to.  Sort of streamlined, not too close to the fuselage,etc.  Then you can place your spring hooks where you need them.  I also lathered copper anti-seize on the exhaust pipe end that fits into the muffler exhaust flange.

Thanks for the info...

Mine cracked and broke off this morning and it did have the reinforcement bracket as well.  Wondering about just doing a 4 into one or 2 into one exhaust for the engine.  It is not like it is actually a muffler just a thin walled pipe with 4 inputs and an exhaust opening.  Thoughts?

Don't know anything about mufflers except the stock UL mufflers that supposedly have been redesigned somewhat. Maybe Helms or Ray can weigh in, or email UL directly.  I am curious as to what the fix may be long term.  When I had mine repaired, I cleaned out the inside (looked sort of like a spark arrestor) piece, and when I installed the exhaust pipe, I took about 3 inches off the end to shorten it up and reduce stress at the muffler flange joint.  Seems to be holding up so far with about 80 hrs since then.

I have been PMing with Evelyn at UL.  I have the older style muffler but I have also talked to Gary Motley and he has had to weld a crack on the new style so I am not sure it is much better.  Evelyn told me she is going to talk with their techs next week.  I think the problem is the exhaust pipe and not necessarily vibrations off the motor.  They are all cracking where the pipe goes into the muffler and since the pipe sits in the (80 to 100 mph plus) slipstream I am sure it is probably putting a lot of stress on that weld.  They probably need to go with a heavier metal on the muffler.

The exhaust pipe is a single one-piece pipe that protrudes into the slip-stream on the Jab design that I mentioned above. Plus, I have a short cabin heat muff mounted on the unsupported exhaust pipe, too.  You would think the stresses would be even higher with no joint and springs as the UL design has.  I think the key is for the pipe to completely traverse the interior of the muffler, penetrate the opposite side and be welded there also.  That would eliminate a tremendous amount of flex on the weld where the exhaust pipe enters the muffler. This sounds similar to the UL design Robert mentioned last September.


I recently received my "new" redesigned muffler from UL.  I did a little fabrication and had a new exhaust pipe bent that will exit through the rear of the lower cowl under the pilot side.  This allows me to support the pipe in at least two locations, near the first bend and then near the exit point from the cowl.  I also added a layer of JB Weld Extreme Heat to all the existing weld joints plus the whole width of the muffler supporting bracket (they only weld it in three spots).  This new exhaust pipe has another purpose in that I can add a Heater Muff to it and reduce the chances of CO getting into the system.

This issue is so hard to understand. I have an original muffler.. 397 hours so far with no problems to this point. Luck I guess.

I shortened the end at installation to just clear the bottom of the cowl as there were already some reports to Robert Helms of fractures. Attempt to reduce stress / vibration from length.

Eventually balanced prop to near zero vibration.

Hope they get this eventually figured out for UL flyers.

Hi David. The muffler design aside, how did you get the tail pipe to fit into the muffler exit tube? Sweat? crimp? My pipes are almost the exact same diameter and no way glide together.


John, mine was a tight fit as well, but eventually went in.  Try polishing the inner diameter of the muffler flange, there may be a burr of some sort.  You could also sand down the tail pipe outer diamter just a smidge and use copper antiseize to help slide it in.  Good luck, let us know when and how it succedes!



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