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CAMIT, the Australian company that builds Jabiru engines to Jabiru's specifications, recently came out with an exhaust seal kit for both the 2200 and 3300 engines. I recently purchased a kit (~$212 USD including overseas shipping) and finished the installation today.
The 3300 normally uses a "slip-fit" connection of 3 headers into 3 muffler inlet tubes on each side of the muffler. These connections are tightly spaced together, precluding any way to effectively use any sort of mechanical clamp or wrap to seal the connections. They also are loose tolerance since you have to get a total of 6 headers and 6 inlets aligned to get the muffler on! Because of the loose fit, there is normally a lot of blow-back exhaust with soot and carbon monoxide blowing into the cowl ... not good!
Ian Bent, the CEO at CAMIT, developed the seal kit and tested it on 10 local aircraft before releasing it for sale. The seal is a triangular stainless steel plate with three close-tolerance holes for the headers to pass through. On the muffler side, the plate has a tapered ring machined around the holes that tends to guide the inlet tubes into a groove around each hole. All of this is held together by additional springs, so that allows some vibration and flexion of the joint - necessary with aircraft exhaust. Additionally, the slight vibration and flexion will, with time, tend to wear and "bed-in" the seal, making it even better! Here's what the seal looks like:
It is essential the inlet tubes' rims are absolutely in the same plane, so I dressed mine with a file and used a Dremel grinder to grind back the spring hangers welded on one of the tubes so the rim can fit in the seal's groove:
Once the seal is in place, you re-install the muffler. There is a stainless band that wraps around the muffler and springs are attached to each end of the band and to the seal. My seals appeared to have a perfectly flush fit, and the springs will keep that fit under compression, but allow for slight movement:
Time will tell how well this works, but the initial fit looks good. I'll update once some hours have been accumulated on the installation.
I've got about 25 hrs on the seals and got a chance to look at them today when I changed the oil on the Jab 3300. The internal cowl was extremely clean and I appear to have a good, tight seal. You can see the picture I snapped vs the last one posted above when I installed them - the seal and pipes look virtually identical - no soot or exhaust streaks. I think CAMIT has a winner with this item!
Just a FWIW for anyone using 3:1 collectors and dual pipes rather than a muffler - CAMit now has an exhaust seal kit for that application, too.