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Repacking Modern Trials Bike Muffler-Ends

Discussion in 'Trials' started by motobene, Feb 24, 2019.

  1. motobene

    motobene Motoing for 49 years Supporter

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    How to successfully re pack a modern muffler with plastic end cap, (`17 Sherco 125/250/300 example).

    I removed the rear fender and did not remove the muffler from the bike. There are 3 screws affixing the Sherco cap. It takes some force to work the cap out then work out the core and packing. Everything is in there quite tightly!

    Here is what puked out:
    IMG_20190223_130456.jpg

    Loud-poppy exhaust will increase over time on any bike with enough hours. That makes a bike sound older than its mechanical age, which sucks.

    The problem was in the perforated-tube holes becoming clogged and the first turn of fiberglass mat wrap around the tube becoming clogged with hardened oil. The communication between the exhaust tube and the resonance chamber of the final muffler was thus becoming progressively lost.
    IMG_20190223_130904.jpg

    Inspection of the inner or first muffler with a flashlight showed how that part - on my bike anyway - runs hot enough to stay pretty clean. Good news, as that part is not serviceable.
    IMG_20190223_143605.jpg

    I toasted the perforated tube with a torch to burn up the oily carbon. Then I used a dinky screwdriver to force carbon out of every perforation hole. After some wire bushing and re painting the tube looked like new. Here it is just prior to rolling some new insulation and the old mat around it.
    IMG_20190223_142634.jpg

    I found the packing to be quite specialized. The mat is dense and has many tiny spike perforations. The top and bottom chamber packing, in contrast, is much looser, being comprised of a stringy Rasta Man-hair-like fiberglass. The long strings are what tipped me off to the assembly solution of pushing the top and bottom Rasta packing in with a rod AFTER the tube with wrapped mat is assembled back into the muffler body. I used a tie down to bias the tube up to make room to force the bottom packing in, then down to make room to force the top packing in.

    I was quite happy to be able to re use the original packing.

    I lit a fire in the mat with my MAPP gas torch (aka propane torch) while holding the mat up to a strong wind. The mat would glow and crackle. I did not let the fire dwell too long so the glass would not melt too much. I'd drop the burning mat on the ground and step on it to douse the fire. I did this multiple times until the critical first-turn-of-wrap was no longer hard like a cold cookie.

    I found the Rasta hair-packing easier to melt so I only burned the more soaked bottom end of each wad.

    The mat and Rasta fibers turned white and became a bit more friable after burn-off. To not have the more friable mat fibers blow out of the perforation holes, I cut a thin one turn wrap in fresh standard fiberglass insulation. Though low density, once wrapped under the higher density mat it was mashed tight and flat.

    Continued in a following post.
    #1
    fprintf and Sting32 like this.
  2. motobene

    motobene Motoing for 49 years Supporter

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    Before wrapping the mat around the tube fit it to the muffler and measure how much it sticks out from the muffler when correctly assembled. You'll need to know that because all the packing will prevent being able to see if the assembly is correct. If not, the tube will stick out farther and not allow the cap to go all the way in.

    To get the new insulation and mat to compress well I used electrical tape, especially at the rear-most end where the Rasta packing would get forced by. Here is the tube-mat subassembly after wrapping, taping, and looping 0.025 stainless wire around. The rear-most end is in the right.
    IMG_20190223_143503.jpg

    With the tube in fully you can stuff in the upper and lower Rasta packing:
    IMG_20190223_150223.jpg
    Note the tie down used to tilt the tube up or down to make more room to jam in the Rasta packing. I did the lower packing first.

    I used a little grease on the electrical tape to help slide the packing past, and grease on the rubber inside the end cap, and on the cap at the muffler interface. The cap popped home with a few taps with a rubber mallet.
    #2
  3. Anachronism

    Anachronism Lived Too Long

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    Nice tutorial! Dumbfounding that manufacturers still produce an exhaust that is not fully serviceable without cutting/welding.
    #3
  4. Cascao

    Cascao Been here awhile

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    Look these Motobene footpegs!
    #4
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  5. motobene

    motobene Motoing for 49 years Supporter

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    Thanks!

    The center part not being serviceable I don't see as a big issue. If one does not run too much oil (80:1 should be the most oil used), the jetting is right, and the rider does not ALWAYS just putt putt around, that part of the exhaust can be made hot enough by heavily loading the engine in a sustained manner to catch the goo on fire and burn things out.

    Yes, over a long time the packing may go cookie-like, but again, burnouts are possible. You just don't want to build up the fuel so much and do too long of a sustained burnout that you can melt the plastic end cap!
    #5
  6. motobene

    motobene Motoing for 49 years Supporter

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    Que lindo!

    Yes, that is one of my Monster Pegs from the 1990s, based on the old standard steel foot pegs. Everyone who tries them SAYS they want them. I've run out of laser-cut stainless steel pieces to make them, however, and I've learned my lesson through the night light project that it's a bad idea to invest in product development for trials.

    Maybe anemic sales is just my fault for not pushing harder, but I'm retired from engineering and have a ranch to run. And if I offer solutions for money I will be:pep. As long as I give away my technical expertise for free there is no issue :-)
    #6
  7. motobene

    motobene Motoing for 49 years Supporter

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    Kinda expected more interest in this. Then again, it took me years to finally do one myself.
    #7
  8. jonnyc21

    jonnyc21 Trials Ninja

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    I should probably have lurked less and at lest liked and/or commented sooner...

    nice job and thanks!
    #8
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  9. HighFive

    HighFive Never Tap-Out

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    Nice job! Very helpful tutorial. I have never burned in a packing material with a torch. Not sure I understand the purpose of that process. You mentioned making it more flexible. Is this something done by factory also, on new installations? Never heard this before.

    HF :lurk
    #9
  10. Junglejeff1

    Junglejeff1 Long timer

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    I don't understand the reason you reused old packing.
    #10
  11. cgunzelman

    cgunzelman Adventurer

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    The parts of the old packing he used look fine to me. Still flexible and porous, not saturated, should still do the trick. The stuff immediately around the perforated tube looked spent. Anyone know where one might acquire a complete new set of packing like this? My silencer came with nothing but a small wafer biscuit of old fiberglass packing. Replaced that with $7 of silencer fiberglass from ebay.
    #11
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  12. motobene

    motobene Motoing for 49 years Supporter

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    Because OE packing is far more sophisticated than the aftermarket packing. I chose to burn the oil out rather than chucking it. Probably good for another two full years of competitions now.

    When I talked to Kevin at RYP about replacement packing, he steered me to the after market Silent Sport or some such. I should find out if RYP can get the OE stuff. Probably expensive, but I think worth the added money.

    Then again, if alternatives work they work, and like I said earlier, whatever works.
    #12
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  13. Junglejeff1

    Junglejeff1 Long timer

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    Not trying to argue but being so critical over muffler packing seems like over thinking. I cannot believe it is going to change the state of tune using using brand x over brand z of packing.
    #13
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  14. cgunzelman

    cgunzelman Adventurer

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    I believe it would help with sound deadening.
    #14
  15. Junglejeff1

    Junglejeff1 Long timer

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    Lol.any packing does that but have found stuff like wall insulation does not last long (used when I was a broke teenager).We could get real critical and start talking about how tight/loose you pack ect.If the whole world was deaf we would not use mufflers.
    #15
  16. motobene

    motobene Motoing for 49 years Supporter

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    JungleJeff1, 'over thinking' about buying no materials and getting an excellent result? ...And taking the time to document it and present it in public?

    I encourage you to buy your brand X or Z materials - whatever materials - do the work, take the photos, and create a thread. Or just add to this one.
    #16
  17. cgunzelman

    cgunzelman Adventurer

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    I think the house insulation is perfect for the very middle of the packing, as that part is the first to need a change. No need to toss out the rest of the packing if it isn't logged with oil and still in a recognizable shape. Bene might get better sound deadening by changing the very middle part more often. That matters to some people believe it or not.
    #17
  18. D2W

    D2W Been here awhile

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    Just for reference, I've had what I consider good success when repacking the mufflers of my 2008 GGs with FMF >4-stroke< repacking material. The 4-stroke material is more rigid than the 2-T packing and enables me to better form the required oval to fit the canister. I also secure the bundle with safety wire/masking tape.

    One complication when reinserting the wrapped core is that a flange on the bottom of the core has to engage a spigot in the muffler body, and it's not the easiest to align the two. A trick I use is to use of length of irrigation pipe whose OD is the same as the ID of the spigot. Then I can slide the core down the length of the pipe and the flange and spigot (generally) align. It's a good idea to measure the core so that you can tell when it's fully inserted into the muffler. And then don't forget to remove the pipe. :)
    #18
  19. Junglejeff1

    Junglejeff1 Long timer

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    Did not mean to offend you.I read all your threads and find them full of great info.Just never heard of anyone reusing muffler packing.
    #19
  20. tomatoe333

    tomatoe333 Long timer

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    I tackled this exact job a few weeks ago. Not having the "real" correct materials, I used three wraps of standard 2-stroke muffler packing around the center core, after burning off the carbon. I reused the original wire to wrap it tight. I ended up using some pink fiberglass stuffed into the muffler can instead of the rasta-packing. I might pull it out again and re-stuff the can at some point when I get some of the correct stuff.
    #20