I repowered a murray 42" in 2004 with a 15.5 B&S instead of a 14. The old motor backfired and caught fire. Now in 2010 the mount strut on the muffler on my 28n707 15.5 B&S motor broke. Then the bolts to the exhaust manifold fell out. They are supposed to be 3/8" shoulder bolts with a 5/16" NC thread, with a 3 9/16" shoulder. This is such a wierd size it is probably patented. I put 4" 5/16" bolts on it with 5/16"x1" washers against the muffler and a nut tightened against the back of the manifold flange for lock, and mowed some more. The washers cut holes in the muffler metal. I tried to order a muffler from turfandtractor.com primeline line, it doesn't cross, and I don't know which of the 4 mufflers in the B&S manual it is anyway. Primeline didn't have any of them. So I ordered a new muffler from smallenginewarehouse.com for the nearest matching engine, an 18.5 hp single cyl B&S. The strut didn't fit the old motor. My local B&S repair shop sold me a non-working coil in a nice B&S box for 50% more than turfandtractor charges for coils that actually work, so I am not going to him again. I welded two 2"x1/8"X1" washers to the muffler, then drilled the washers to 5/16" on 1 7/8" centers like the manifold . I welded a bracket to the muffler over the old one and took it out to the country where the mower is. The bracket interfered with the starter, I had to saw it off. The muffler to manifold holes were a little off, but 30 minutes with a rat tail file got the bolts to line up. I installed the muffler on two 5/16" x 6" all thread bolts, with double nut counter tightened at the outside and a nut counter tightened at the back of the exhaust flange to keep it locked. I got 2 acres done before the bolts fell out again. The threads were all worn off where the muffler washers had been resting on the bolts, so I can't use those bolts again. I have ordered pinched top locknuts, and 5" all thread grade 8 5/16" NC bolts from mcmaster.com, but though they said they had stock they are having trouble shipping. I've got the muffler back in town to weld another mount bracket on it. The motor spits fire 2" out the exhaust manifold and I only mow when it is dry, so I will not be mowing without a muffler. Any comments?