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Muffler modded my 7900 today pics

Discussion in 'Chainsaw' started by scotclayshooter, Mar 9, 2008.

  1. scotclayshooter

    scotclayshooter Addicted to ArboristSite

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    Hi guys well it dont even have a tank of fuel through it yet but i had some spare time this morning.
    First i removed the muffler from the saw (take notes Brownpot Deaton lol)
    I heated up the crimp and a bit at a time prized it up with a narrow bladed screwdriver until i coild get a hold of it with a pliers.
    I did this around the bottom and one side gave it a good wiggle and the 2 parts seperated!

    The baffle just fell out so i cut the complete end off and rounded of any rough edges with the dremel.
    I did a quick measure and found that the area under the deflector would be as near as :censored: 125% of port area, So i cut a couple of grooves with the dremel and got a junoir hacksaw in and cut the old hole out whole lol
    More tidying up and maximizing area with the dremel.
    then re asembled the 2 halves bending and hammering the baffle back into place, Re fitted the screen then fitted it all back on the saw.
    Now i know it has a rev limiting coil Grr i tuned it back to 13,480 so it should still be a little rich for now.
    Its not much louder! and i havnt had a chance to cut with it yet, Roll on next week!

    Heres the original baffle
    [​IMG]

    The modified one
    [​IMG]

    Copmare the old and new holes
    [​IMG]

    And the completed muffler
    [​IMG]
     
    West Texas likes this.
  2. Tzed250

    Tzed250 Account Hold

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    Nice work! not much louder, huh? That baffle sure looks stout. How long did it take you?
     
  3. scotclayshooter

    scotclayshooter Addicted to ArboristSite

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    About an hour start to finish, O yes that baffle is strong, 0.047 and spot welded at the end! Someone suggested hammering it through with a bar but mine would have damaged the muffler before it would have bent!
    Its not really that much louder not like the 036 or the FS250 (it will make your ears bleed)
    The original hole was 0.557 or 14.16mm round
     
  4. Tzed250

    Tzed250 Account Hold

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    Shoot! Thats a big hole! The stock hole on the 660 was only 10mm!!!
     
  5. bwalker

    bwalker Resident Hack Sawbuilder Exposer

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    The 7900 isn't near as choked up as some saws. When I muffler modded mine I simply cut the baffle up with a die grinder and ditched the screen.
    This way I didn't have to take the muffler completely apart.
     
  6. scotclayshooter

    scotclayshooter Addicted to ArboristSite

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    That 14 mm hole must be a restriction its even flared inwards!
    That cant be good for gas flow.
    I was suprised to find it only had 1 piston ring!
     
  7. Andyshine77

    Andyshine77 Addicted to ArboristSite

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    Nice job Scot:clap:

    Yup only one ring, stock cold compression on a 7900 is 160+ I don't think removing the internal baffle on a 7900 is necessary, I think it has more than enough sqmm.
     
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