Richard Pike
Joined: 09 Jan 2006
Posts: 1671
Location: Blountville, Tennessee
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 Posted: Sat Mar 19, 2011 5:55 pm Post subject: Muffler crack |
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During preflight this afternoon I found a crack in the muffler/expansion pipe junction of my 582 muffler. This same general area has caused me problems before with different Rotax engines, and has also caused several other local flyers crack problems in this same place.
Attached is a picture of the muffler after I welded it and after I got done flying for the day. Thought about taking a picture before I welded it, but it was already 6 PM, and I wanted to just fix it and go.
Welded it on the airplane, obviously haven't painted it yet. The red line is where the crack was, discovered the crack by first seeing exhaust carbon residue that had come out of it. Since the airplane was already out on the runway in front of the hangar, rolled the welding cart with the oxy/acetyline tanks out to the airplane. Once I got the metal red hot, I could see the crack was at least an inch longer to the left and 2.5 inches longer to the right than the original crack appeared to be, so it was progressing.
My MKIII uses what they call the "Quicksilver" style expansion pipe, this is the first time I have seen a problem with this style, all the other failures have been with the "Curlyque" sidemount style like the Kolbs typically use, and have involved 447, 503 and 532 engines.
On those, the failure typically begins on the weld along the outside of the pipe, the pipe splits along the edge of the welded flat seam and then the pipe begins to crack and separate around the junction of the pipe and muffler. Several of us have discussed this and it is our opinion that the pressure pulses eventually fatigue the welded joint and cause a crack.
However, one of the failures was on a 503 about 12 years ago and in that one there were two cracks that started right in the rounded side of the curlyque. Apparently that portion of the pipe takes a lot of pressure pulse abuse.
Ed and I discussed this for a while this afternoon, because he has a curlyque on his FSII, and you cannot see the front side of the welded seam from the rear of the wing. The only way you can see it is to stand on a stool in front of the wing and look over the wing to see it, but IMO, this ought to be a checklist item, because we have seen enough of them go bad that it is an obvious weak point.
And if you are flying and it occurs to you that maybe your engine is a bit louder than it was - find a suitable place to land and check this area out. When the whole side half of the curlyque came loose on my 532, I was 5 miles from home, and by the time I got on the ground, the only thing holding that half of the curlyque expansion pipe to the airplane was the area adjacent to the ball joint, everything else had already broken. The Ivoprop would not have been happy... AND IT WAS LOUD! The wife heard me coming 3 miles away... From inside the house... With the doors and windows shut...
So if your Rotax 2-stroke suddenly gets really loud - land. Unless you have a metal sheathed Warp Drive prop that can suck up that detached half, (good test, eh?) and would prefer to just buy a new cone for $200 rather than repair yours. Then you can keep going...
Richard Pike
MKIII N420P (420ldPoops)
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