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25cc Chainsaw porting

Discussion in 'Chainsaw' started by Pakai Boti, Feb 3, 2019.

  1. Pakai Boti

    Pakai Boti ArboristSite Lurker

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    Hello
    My Zenoah g2500 chainsaw has seized.I am looking to buy a new top end, and I would like to port it somehow.Can you give me some advices where should I take some metal off? 51128908_379326522855310_6241070948376641536_n.jpg 51182288_1028770787332292_961517511126286336_n.jpg 51255431_232427827644480_2940619929814040576_n.jpg 51417433_403258967090323_70881919755091968_n.jpg
     
  2. Ax-man

    Ax-man Addicted to ArboristSite

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    Gotta pic of the intake ??? That is one funky looking exhaust port . Hogging out that whole port might be overkill for a 25 cc saw . I would widen and open up that c looking thing in the middle of the port for starters . Why is that even in there ??? Never seen anything like that . Not trying to be smart arse but that is one rough looking cylinder . It looks like it has been run with an overly rich oil to gas mix .

    How about the muffler ?? Can you do anything with that . I would start there before messing around with the ports.
     
  3. wcorey

    wcorey ArboristSite Guru

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    Widening the intake and exhaust ports is usually a good place to start, just don't go past the width of the piston skirts or near ring ends.
    Really you need to map the stock timing numbers before changing timing, though typically stock saws benefit from a little more intake duration by lowering of the intake port or taking some off of the piston skirt.
    Sometimes raising the transfers helps but it's chancy without knowing what the blowdown number is.
    Raising the exhaust port can help with rpm's but can also kill compression and usually the transfers need to be raised along with it.
     
  4. NSEric

    NSEric ArboristSite Operative

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    I have one of these on the way and have been waiting for it so I can port it.
    I'd do the following and widened the intake a hair, you will have to make the muffler and gasket match the larger port too, I was a little shaky drawing on the pics lol.
    51128908_379326522855310_6241070948376641536_n.jpg
     

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  5. Honyuk96

    Honyuk96 ArboristSite Member

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    Pm Frank Jizzmo, he'll sort this out quick like.
     
  6. Honyuk96

    Honyuk96 ArboristSite Member

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    Pm Frank Jizzmo, he'll sort this out quick like.
     
  7. Pakai Boti

    Pakai Boti ArboristSite Lurker

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    Here are some pics of the intake
     

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  8. Pakai Boti

    Pakai Boti ArboristSite Lurker

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    I haven't found anyone by this name :(
     
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  9. TheBrushSlasher

    TheBrushSlasher I have chainsaws and chainsaw accessories.

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    Don't feed frank!

    Dude is a scammer. See stihl 462 thread.
     
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  10. rmihalek

    rmihalek Where's the wood at?

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    What is that gigantic chunk of metal blocking the exhaust port? Is that the piston skirt that exploded when the engine seized?

    I have found that the rate-limiting step in these repairs is the availability parts.
     
  11. Little Al

    Little Al Addicted to ArboristSite

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    For the price of what you are going to spend, search around & you'll possibly get 1 or more saw in the 244F Oleomac make /model, possibly a poor or non runner requiring a small item ie carb kit to get it up running properly (set up/tune & you'll have more power than trying to extract "umph" from 25 cc's I bought 4 (job lot) for 20€ got 2 running with setting up 1 carb kit & 1 recoil cord kept 2 & flipped 2 for €35each =2 saws & profit of over €50 's
     
  12. TheBrushSlasher

    TheBrushSlasher I have chainsaws and chainsaw accessories.

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    Thats actually part of the cylinder casting. I looked a few photos of new zenoah 25cc cylinders that have that.
     
  13. NSEric

    NSEric ArboristSite Operative

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    I finally got my top handle.
    I did a super quick port job and muffler mod, it gained a little power and about 1000rpm. I didn't want to tear it totally down as it runs pretty good out of the box and is a pita to work on.
    I stuffed the cylinder with a rag and ground the exhaust port a bit like the red line in the pic, this doesn't change the timing as the top of the exhaust port is still the same at the highest point but the top of the port is flatter now so it opens up more of the port sooner. I sanded the edges of the port so the rings wont catch on it.
    I also drilled a hole in the baffle in the muffler through the opening.
    Here's a vid of it cutting, I skipped the porting part on purpose in the vids description to avoid bs on youtube about porting like that.


     

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    dswensen and scottr like this.

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