The muffler on the Briggs and Stratton engine was cracked off from the inlet pipe and the baffle inside the muffler was loose.
The root cause of the cracked pipe was the fact that the screw which attached the muffler to the engine had loosened and fallen off. This meant that the entire weight of the muffler was cantilevered from the pipe, which caused it to crack next to the weld joint that attached the pipe to the muffler. The muffler bracket was located correctly at the center of gravity of the muffler. If the screw was in place it would have properly supported the weight of the muffler. A new muffler assembly, which includes the inlet pipe and flange cost $195, so I figured it was worth a try to weld it. My concern was that the muffler and pipe had been exposed to carbon from the exhaust for 10 years and had surely absorbed some of it. This would have converted the muffler and pipe from mild steel to medium carbon steel, which is more susceptible to cracking.
The problem with the loose baffle was the baffle was too sloppy of a fit in the muffler can for the MIG spot weld to penetrate through the outer layer of the muffler can to fuse with the baffle on the inside. Only one of the three MIG spot welds had penetrated through the outer can to the baffle.
To fix the loose baffle, I cut the can open and plug welded the baffle to the can and then welded up the can. I know that plug welds aren't the best in fatigue but with three plug welds the baffle really had nowhere to go even if one or more of them failed.
So far it made it through the entire mowing season, but I'm still worried about cracking.
What do you think?