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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While I was cleaning up from my oil cooler leak,  I decided to look at my muffler again.  I have the newer style as noted by the web as in David's lower picture.  That web cracked and was coming loose in all the places where it was attached to the muffler.    Also,  there was another crack forming outside of the weld from the tailpipe holder.   It was about a cm away.  I'm having it re welded and will weld the reinforcing gusset completely down to the muffler.  Not just tacked in three places.   The fact that the metal was fatigued and failing away from the crack makes it more likely in my mind that this problem is not completely fixed.  Look closely at your muffler. 

Has anyone done prop balancing yet?  It seems like there is a pulse/vibration  off this engine (350 iS)  that may be greater than some of the aircraft design and parts are designed to hold.  ( Eg horizontal tail that also had to be reinforced).  

Any thoughts? 


Just talked to Gary Motley last week, he is working with friend on prop balancer. You might contact him to see what they come up with. Maybe you can talk him into doing a You Tube video on it.



I posted on the ULP owners forum about prop balance. It was within reason at the start but was able to almost eliminate the vibration after the balance. I don’t think harmonics from the engine is causing problems but just an opinion. 

Fred, that is disappointing to read!   I ask the guy who fixed my muffler, who is a certified aircraft welder, what he would do to improve the muffler.  He said "make it with thicker material."  If it cracks again, I'll have him fabricate one for me but with thicker s/s material.  Meanwhile, "fly it and watch it!" 

Regarding dynamic prop balancing, I have no backing plate on my spinner and at a loss as to where I would attach balance weights if needed.  I think I have to make a ring (like the prop crush plate) with a slightly larger outer diameter than the prop flange for attaching weights.  Open for ideas.

My muffler that cracked had the piece already to stiffen the flange. I had my welder go ahead and completely weld the extra support to the muffler body. It was just attached at three small areas. The main fracture was outside the weld on the flange. 




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