Muffler Repair for Honda Forman 400 ATV
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  1. #1
    Join Date
    Mar 2014
    Location
    Troy MI
    Posts
    134

    Muffler Repair for Honda Forman 400 ATV

    The muffler on my customers Honda Forman 400 ATV rattled. A new muffler from Honda cost $629. (However, an aftermarket version would be less expensive). I have had good luck repairing mufflers, even though you would think the high carbon from exhaust would make it difficult to weld without cracking. First, I cut off the end of the muffler using my favorite Super Slicer Plus cut off wheel on my Matabo 6” grinder. Picture 4 shows the loose pieces that were rattling around. Picture 5 shows one of the bulkheads of the muffler with a large piece missing. If you look carefully at the bulkhead beyond this one, you can see a crack in the bottom. I did not bother to repair this one because the muffler was not too loud and it would have significantly increased the scope of the job.

    1. Entire muffler
    2. Cutting off end cap
    3. End cap cut
    4. Loose pieces in muffler
    5. Broken bulkhead
    Attached Images Attached Images      
    Smith Oxyacetylene Torch
    Miller Dynasty 200DX
    Lincoln SP-250 MIG Welder
    Clausing/Coldchester 15" Lathe
    16" DuAll Saw
    15" Drill Press
    7" x 9" Swivel Head Horizontal Band Saw
    20 Ton Arbor Press
    Bridgeport
    Lincoln LE 31 MP & Lincoln 210 MP

  2. #2
    Join Date
    Mar 2014
    Location
    Troy MI
    Posts
    134

    Re: Muffler Repair for Honda Forman 400 ATV

    I bead blasted the bulkhead plate to remove the rust and carbon. I sanded the ID of the can with a Scotch Brite pad soaked in Acetone. In picture 6, you can see the new piece in place that I eventually welded to the can and the existing bulkhead (sorry I do not have a picture of this weld). Picture 7 shows me welding the next bulkhead in place. Notice the orange spot on the outside of the can of the muffler indicating good heat penetration. Picture 8 shows the washer that I welded to the bladed bulkhead. I added a washer because the outside of the bulkhead was thin but the center was solid. I wire brushed the bulkhead and cleaned it with Acetone, but in hindsight I should have bead blasted the vanes of this bulkhead to better clean it up. As you can see, the weld has some contamination in it. The weld in picture 9 that attached the washer to the ID of the can went better because it was cleaner. The last picture, #10 shows the weld to attach the end cap to the end of the muffler.

    6. New bulkhead installed
    7. Welding new bulkhead
    8. Washer Added
    9. Washer welded to muffler
    10. End cap welded back on

    -Don
    Attached Images Attached Images      
    Smith Oxyacetylene Torch
    Miller Dynasty 200DX
    Lincoln SP-250 MIG Welder
    Clausing/Coldchester 15" Lathe
    16" DuAll Saw
    15" Drill Press
    7" x 9" Swivel Head Horizontal Band Saw
    20 Ton Arbor Press
    Bridgeport
    Lincoln LE 31 MP & Lincoln 210 MP

  3. #3
    Join Date
    Feb 2012
    Location
    Sweden
    Posts
    643

    Re: Muffler Repair for Honda Forman 400 ATV

    Nice repair.

    I repaired a chinese stainless ATV muffler this summer, the muffler wall cracked around the tube. The basic problem is the bad design, the muffler is heavy and is only hanging from the frame at the rear end, the next mount is on the tube, a muffler length ahead of the muffler. In combination with the muffler wall being only about 1mm/0.040" it eventually breaks.
    Welded using my Dillon (a.k.a. Henrob) O/A welder, and I added two extra supports to where a larger diameter tube is welded to the inside of the wall, for extra support (later versions had support there from the factory). Remains to be seen how long it lasts.

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    Name:  DSC04861.jpg
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Size:  74.3 KB

  4. #4
    Join Date
    Mar 2014
    Location
    Troy MI
    Posts
    134

    Re: Muffler Repair for Honda Forman 400 ATV

    Quote Originally Posted by G-son View Post
    Nice repair.
    The basic problem is the bad design, the muffler is heavy and is only hanging from the frame at the rear end, the next mount is on the tube, a muffler length ahead of the muffler.
    In my personal experience, I have not yet seen a failure where "Bad Design" was the root cause of the failure. I have seen several cases where a missing screw caused the heavy can of the muffler to bounce up and down, which caused the weld that attached the can to the pipe to fail. Below is a picture from Toro zero turn that I repaired in which a missing screw caused the pipe failure. Is there any way that you can add an additional screw somewhere to help support the heavy can?

    -Don
    Attached Images Attached Images  
    Last edited by Don52; 11-03-2018 at 09:00 AM.
    Smith Oxyacetylene Torch
    Miller Dynasty 200DX
    Lincoln SP-250 MIG Welder
    Clausing/Coldchester 15" Lathe
    16" DuAll Saw
    15" Drill Press
    7" x 9" Swivel Head Horizontal Band Saw
    20 Ton Arbor Press
    Bridgeport
    Lincoln LE 31 MP & Lincoln 210 MP

  5. #5
    Join Date
    Feb 2012
    Location
    Sweden
    Posts
    643

    Re: Muffler Repair for Honda Forman 400 ATV

    Quote Originally Posted by Don52 View Post
    In my personal experience, I have not yet seen a failure where "Bad Design" was the root cause of the failure. I have seen several cases where a missing screw caused the heavy can of the muffler to bounce up and down, which caused the weld that attached the can to the pipe to fail.

    Is there any way that you can add an additional screw somewhere to help support the heavy can?
    This is how it is built, on a picture I found online. The red circle on the tyre shows approximately where a tab on the tube is bolted to the frame (rigid mount, single M8 nut & bolt), the rear circle shows the flimsy sheet metal loop (with a rubber layer inside) hanging from a single bolt above, that the rear of the muffler hangs from - this allows the muffler to move about quite a bit when the ATV bounces on uneven surfaces.
    I would have preferred a more rigid rear mount, and possibly another mount at the front of the muffler (green circle) to hold the weight and make sure the muffler doesn't move around and bend the joint between tube and muffler wall, but I only had the exhaust to work with now, not the complete ATV.
    I helped the local seller of these machines several years ago, and at least 5 mufflers on machines he sold broke in a year. After that the factory added a "cone" over the joint between muffler and tube, attaching the stronger area ~1" outside the tube on the wall to maybe 2-3" out on the tube - like my reenforcing bars, but in the form of a cone going all the way around. As far as I know, no mufflers broke after that, and the fact that the problem showed up on many machines before the factory redesigned the part suggests the problem was a bad design.

    I agree it is rare that a bad design is the cause of failures, but in this case it looks like the chinese tried to cut one too many corners to save money.

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  6. #6
    Join Date
    Mar 2014
    Location
    Troy MI
    Posts
    134

    Re: Muffler Repair for Honda Forman 400 ATV

    Quote Originally Posted by G-son View Post
    I agree it is rare that a bad design is the cause of failures, but in this case it looks like the chinese tried to cut one too many corners to save money.
    I agree with your conclusions. Thanks for the excellent description. Your picture made the situation very clear.

    -Don
    Smith Oxyacetylene Torch
    Miller Dynasty 200DX
    Lincoln SP-250 MIG Welder
    Clausing/Coldchester 15" Lathe
    16" DuAll Saw
    15" Drill Press
    7" x 9" Swivel Head Horizontal Band Saw
    20 Ton Arbor Press
    Bridgeport
    Lincoln LE 31 MP & Lincoln 210 MP

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