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Stihl Ms 391

Discussion in 'Chainsaw' started by Davidkaram, Jan 11, 2018.

  1. Davidkaram

    Davidkaram ArboristSite Lurker

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    Hi I have an MS391 that wouldn’t pull the pull cord is good I tried to reverse the fly wheel by hand it did for a certain point but it doesn’t turn completely , and I can’t get it to move 1 inch with or without the pull cord any help ?
    Note I removed the spark plug it’s not flooded and it wouldn’t move as well without the spark plug
    Thank you all...
     
  2. merc_man

    merc_man Addicted to ArboristSite

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    Is fly wheel hitting coil?

    Sent from my SM-J320W8 using Tapatalk
     
  3. Andyshine77

    Andyshine77 Addicted to ArboristSite

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    You're not going to move the flywheel far with the starter still on the saw. Try spinning the flywheel counterclockwise.
     
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  4. Davidkaram

    Davidkaram ArboristSite Lurker

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    Thanks for ur reply no the wheel is not hitting the coil
     
  5. Davidkaram

    Davidkaram ArboristSite Lurker

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    Thanks for ur reply, I tried it turns a little bit clockwise but it doesn’t move the other direction
     
  6. Andyshine77

    Andyshine77 Addicted to ArboristSite

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    With the spark plug removed shine a light in there and rotate the flywheel as much as you can. If the piston doesn't move when you turn the flywheel, you've got problems.

    Sent from my LG-H871 using Tapatalk
     
  7. earlthegoat2

    earlthegoat2 ArboristSite Guru

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    Had this happen on a 311.

    Pull muffler and look at the piston if you can. The 311 had been straight gassed when it locked up and the piston was trashed.

    I’ve also had this happen on some other power equipment. These happened to be Echo SRM 255s. Bearings locked up and piston trashed from straight gas.
     
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  8. deaves61

    deaves61 Addicted to ArboristSite

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    May want to check the crank bearings.
     
  9. sawfixer

    sawfixer ArboristSite Lurker

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    I rebuilt a MS391 which did the very same thing. The factory FAG bearings with the plastic ball retainers failed and spilled some of the balls into the crankcase. Fortunately, it didn't trash the topend. Mine made a rattle sound when shaken.
     
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  10. Delano1981

    Delano1981 ArboristSite Member

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    I have an 029 that was unusually hard to pull, and once started would only idle and then die immediately when any throttle was given. It took me quite awhile to finally find the problem. The coil wires were rubbing on the back of flywheel causing drag on the flywheel. It runs great now since I moved the wires out of the way
     
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  11. Davidkaram

    Davidkaram ArboristSite Lurker

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    I will try to do so thank you for your help
     
  12. Davidkaram

    Davidkaram ArboristSite Lurker

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    I will look at it I hope it can be fixed with me it’s a 2017 new model
     
  13. Davidkaram

    Davidkaram ArboristSite Lurker

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    I will thank you
     
  14. Davidkaram

    Davidkaram ArboristSite Lurker

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    I’m not sure if it’s the same here as it’s a 2017
     
  15. Davidkaram

    Davidkaram ArboristSite Lurker

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    Woow that’s interesting but here I can’t find the coil stuck
     
  16. Davidkaram

    Davidkaram ArboristSite Lurker

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    Hi I did that the piston turn but it then get stuck anti clock wise
     
  17. Andyshine77

    Andyshine77 Addicted to ArboristSite

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    The piston turn? Sorry I'm not following you. Are you saying you rotated the crank and the piston moved freely up and down?

    Sent from my LG-H871 using Tapatalk
     
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  18. Davidkaram

    Davidkaram ArboristSite Lurker

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    HI thanks for ur reply and help
    the fly wheel moves half a round by that moving the cylinder,but then get stuck and I have to move it the other way, until its stuck again, I feel something is stuck inside it, I cant as well disassemble the cylinder or the muffler its not clear how to! very complicated,,, and there is no such videos any where to explain how to fix since it is a 2017 new model,,
     
  19. earlthegoat2

    earlthegoat2 ArboristSite Guru

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    Sounds like something is jamming in the squish band.

    Use a screwdriver to pry out the plugs on the front of the muffler. Then unscrew the muffler with a T27 torx driver.
     
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  20. jeremyc

    jeremyc ArboristSite Lurker

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    Any story of what was going on before this happened? Were you running it or is this something you acquired?
    I would pull the clutch drum and clutch off of the other side to make sure nothing is jammed in the clutch/case.
     
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