cracked exhaust on 912ULS

I've seen many and exhaust pipe or muffler welded without any issues. That said it all depends on how good a welder your pick. Find a good one that knows their stuff. I've been lucky at my airport field. We have one of the best I have ever seen. He even makes muffler systems for certified aircraft and makes beautiful welds.

Hi RL,

In my limited experience, welding up a crack is not the same as say replacing & welding on a new section or building from scratch😈

That looks very much like the OEM muffler Kitfox used to supply. It was not made by Rotax, but by some other manufacturer contracted by Kitfox. They quit supplying this muffler several years ago due to cost escalation, etc. Kitfox now uses the genuine Rotax muffler/exhaust system. I went thru this about 6 months ago, replacing my old cracked (1500 hour) Kitfox muffler on my 912 ULS with a new Rotax unit. The Rotax muffler looks to be higher quality and it is a drop in replacement for the old Kitfox supplied muffler-ALMOST. The main difference is the exhaust exit pipe coming out the end of the muffler is not centered on the end cap and is several inches longer. This means you will have to remodel the exhaust pipe exit hole on your fiberglass cowling. Also, the whole exhaust system (4 header pipes) must be replaced because the old Kitfox supplied headers do not fit into the Rotax muffler. Bottom line be prepared for quite a high total cost. Once it is in and cowl modifications made, you will be happy with it.

Update. I had a mobile TIG welder come out and weld my muffler, it was $400. Well, it lasted about as long as I expected - 6hours. It cracked again near the weld which means to me that at about 900 hours, this exhaust system is at the end of its service life. (note: this original muffler was manufactured by Kitfox, not Rotax)

By the time it cracked, my new exhaust system had arrived. Just a note, the Kitfox exhaust system I purchased 4 years ago cost $1100, the new Rotax one (973-383) is $3529!! Holy Guacamole! It appears to be a much beefier design so I suspect it will be worth it. 

It was actually a big project to replace the exhaust system. Since the muffler diameter on the new 973-383 is much larger than on my 2015 912ULS, I had to re-route the oil lines to keep them away from the hot muffler. The EGT sensors had to be replaced because the old ones were simple stainless steel clamps and the new ones are the 8mm threaded ones. Also had to re-work the cowl becuase the stinger exits about 3" from where the old one did.

As an aside, because of the outrageous price of replacement parts now I am actually planning on buying and installing a new 912ULS and then using my 1200 hour one for parts.

I hear you Dan. It sounds familiar, but I only had to reroute one oil line due to the larger diameter muffler (its only a little larger).

I also reused my stainless steel clamped EGT sensors by drilling the appropriate holes in the headers. The threaded ones you refer to are not correctly located at 100 mm from the exhaust flanges, as specified in the Rotax installation manual. I plugged the threaded ones with 8 mm SS plugs (available from Rotax).