ORIGINAL: coralcape
I have done many homebuilt mufflers and the problem I find is vibration. The aluminum rod just doesn't have the strength. I have supported the exhaust pipe and this helps somewhat. My solution is to run the exhaust pipe all the way thru the muffler. Drill exit holes as needed in the exhaust pipe. This extra length and having the end of the exhaust pipe bearing on the wall of the muffler seems to do the job in most cases. I don't think heat is the problem,as the melting point of the rod is much higher than the engine will ever get to. Good luck, red
For smaller engines it will work ok. The tip about running the pipe all the way to the opposite inside of the box is good. I have made a tab and secured it with a nut an bolt withe the end peened over. This gives an oppertunity to perforate the pipe with a zillion itty bitty holes. Keep the area near the exhaust port solid. It will cut the sound dramatically and maintain flow.
The last attempt for my 65cc was done this way. The pipe did not fall off. The solder did melt and the pipe ratteled around so much as to make the exit hole in the can grossly ovesized. It will melt in big engines....really.
The exhaust gasses are very hot even though the head does not get hot enough to melt the solder. Up to 50cc, a BME-50 clone, it has worked out fine. I make the flat ends of the cylindrical muffler out of flat 3/16"-ish stock that is turned on a lathe with a shoulder that fits the cylinder snug. Tube part of the cylinder is made of aluminum fire extenguisher or aluminum pressure tank. A draw bolt holds it together. The body of these mufflers are pleanty tough. Perhaps the solution is to put a bunch of little holes instead of an exhaust pipe? I'll have to try that one day.