1. When diagnosing an issue, or showing off your tractor or implement, it's important to add images so we all know what you're talking about. Especially when it comes to issues and repairs it's important to include as many images as possible to help our members diagnose your issue. To upload images, use the Upload a FIle button found towards the bottom right of the post response box or a new thread, If you ever have questions please feel free to contact me, My username is Austin.
    Dismiss Notice

Briggs single cylinder mufflers

Discussion in 'Murray' started by indianajo, Aug 17, 2010.

  1. indianajo

    indianajo New Member

    Apr 15, 2009
    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?
    Last edited: Aug 17, 2010
  2. raylinkz

    raylinkz Micro Farmer

    May 28, 2010
    JD Weld. Tap and Die the thread you want. Or JD Weld the bolts into the hole with a new muffler and just figure on having to tap and die when removal necessary. Use the original, not the new quick formula. Use a small round wire brush to clean the bolt hole as good as possible. I've used this stuff in some grungy places and it's held up very well. Never used it on a muffler bolt but it has worked on a cracked manifold. If you try it, let me know how it worked.

  3. dangeroustoys56

    dangeroustoys56 Collector Supporting Member

    Jul 26, 2010
    Wow- ive never had a muffler bolt come out- i never seize mine so they dont lock into the block.

    Most mufflers use a metal tab on the shield to 'lock ' them in place- You could go one step further and drill the heads of the bolts and wire to lock them in place ( im not sure what a thread locker would do in the heat) - as for the metal tearing, id weld a thicker piece of metal to it.

    Years ago i had the muffler blow apart on my craftsman- i took two bolts and drilled holes in the halves , bolted them together welded the nuts on to the case of the muffler and bolt and also tack welded the muffler back together- never came apart after that.

    About the fire from the muffler- could be running a tad rich.....
  4. indianajo

    indianajo New Member

    Apr 15, 2009
    Thanks dangeroustoys56. Was thinking about drilling bolts and nuts and a cotter pin, but the restricted space behind the exhaust manifold inhibited me. The 5/16" x 5" full thread grade 8 bolts came in from mcmaster, also the pinched thread (no plastic) locknuts. By spinning a grade 2 nut against the head of the 5" bolt, they were the right length without cutting, and I got the locknut on behind the exhaust manifold flange. Welded a new bracket on the original muffler and by drilling and rat-tail filing, got it to fit the block mount. Wow, they really want to sell you the parts they can't identify, if you use longer than a 7/8" long regular hex head bolt into the block the head hits the starter. Their original bolt (in the grass now) has a 3/8" head on a 5/16" shank bolt. Had a grinder out in the country, and a triangle file, so was able to shorten a 1" long bolt and get the muffler-block bracket to work. Muffler holding on fine with all the new parts. That 15.5 really chews up high grass if it is running right, try one on you murray 42 if you get the chance. Ground speed ls limited by the slipping of the deck belt, not any limitation of the motor. I'm knocking down 36" grass and weed at speed 2.