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stihl chainsaw... weird object in muffler?

Post in 'The Gear' started by clemsonfor, Jun 20, 2013.

  1. clemsonfor

    clemsonfor Minister of Fire

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    OK I have just what my title says. I have a ms390 saw. About 9 yrs old.
    Now I'm pretty good with them
    I have even pulled this one apart when the decomp valve fell apart and the stem wedged the piston to the head. I have rebuild the varb and on and on. Anyway after I used it the other day I heard a metal clanking.I was alarmed so when I got home I pulled the muffler. I can see what looks like a metal cyl about the size of a 3/16 bolt shaft through one of the bolt holes?? It could not have come out of the cyl as the outer chamber appears sealed to an object that size from the motor side. Any ideas what it is? Having no idea what the insides of these look like I don't know and am not going to cut it to find out? Just running it as is but it sounds like there is something in my cyl or the rod is bustedwn I move the saw when off!

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  2. Joful

    Joful Minister of Fire

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    Part of that old busted decomp valve? <>
  3. ScotO

    ScotO Guest

    Better tear into it before it turns into a grenade....sounds like you possibly could have a bad rod bearing or something........

    Easier to fix when it isn't blown up......a lot more costly when it blows up!
    Nixon likes this.
  4. MasterMech

    MasterMech Guest

    A hollow cylinder in the muffler...... could be the tube that the bolt passes through. Will one of the muffler studs fit through it?
    rkshed and ScotO like this.
  5. clemsonfor

    clemsonfor Minister of Fire

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    No its in the muffler!! There is no way the rod bearing could get inte muffler. I have pulled the muff;off the saw and its in there. Like I said it looks like it could be 1/2 long by maybe 1/4 thick. I can see it through the hole that the mounting bolts go through. I ran a tank through the saw today. If it was rod bearings it would of grenades by now.
    Joful likes this.
  6. clemsonfor

    clemsonfor Minister of Fire

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    I can't tell if its hollow? But look; at the size I bet a bolt could go through it?
  7. MasterMech

    MasterMech Guest

    Does it look like one of these?
    [​IMG]


    This would be my solution. ;)

    Note that if it is indeed the inner guide tube for the bolts, then the muffler will not torque down/seal properly. I would replace it before too long. If you get an original muffler (new or used) I would modify it for better flow for sure. Poor MS390 is one of the most choked up factory mufflers I've seen. Note that the muffler I linked to on ebay (above) already has 2 additional slots in the muffler.

    Here's what I did to the last MS390 I had in the shop.

    029 Muffler Modified.JPG

    Don't forget to carve open the deflector a bit too, otherwise it becomes the bottleneck.
  8. clemsonfor

    clemsonfor Minister of Fire

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    Thought about modding it. And also just getting a new muff. I did not mod it as i did not want to have to tune my Carb but I have been into it for other reasons so its not factory set any more anyhow. I'll just take this as a point to do that. I already am missing a stud that I not replaced that was stripped when I pulled saw apart. I do have a replacement though.

    So this is a muffler bearing?: -)
    pyroholic likes this.
  9. ScotO

    ScotO Guest

    in your original post you stated it sounded like something was in the cylinder.....that's where my original thoughts were. A rod bearing (crank end) could get into the cylinder via the lungs on the sides of the cylinder.......and eventually wind up in the muffler......
    But after re-reading your original post (its kinda confusing), I think MasterMech nailed it. Its most likely a spacer that keeps the muffler from collapsing when you torque down the screws. There's no better.time to mod the muffler while.you have it apart. And tuning a carburetor is easy as pie......don't let that stop you from getting more out of that saw!!

    Dual port that damm thing and make yourself smile!!
  10. Boog

    Boog Minister of Fire

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    I'd take a good close look at the threads in the cylinder hole where that "stripped" bolt came from. Not sure which is harder, the bolt or the cylinder metal (probably the bolt), but you might have the threads stripped out of that hole. Might need to tap it out to the next larger bolt size to be able to get a bolt to torque up properly in it. Of course, then the larger bolt might not fit through the inner sleeve!
  11. clemsonfor

    clemsonfor Minister of Fire

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    ??? Not on this stihl saw? There is a slot on the cyl head and there is a square end on the bolt that slides in. Then a nut that tightens on the stud.
    MasterMech likes this.
  12. clemsonfor

    clemsonfor Minister of Fire

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    Yea i re read my post when i read your original one. It was all garbled up but i was posting on a phone and i am to cheap to buy the app, so its pretty tough to proof read and look it over.

    I also think faster than i can type, esp on a phone where its auto correting things and just messing up due to keyboard.

    But yea your right it the bearing breaks apart it can suck it in though the side port. But again i was not clear i guess. the part is in that outboard chamber from the saw, looking at the design of the muffler when i had it off the saw there is no way a rod bearing could make its way into that outward chamber, it would just sit in that main "hallway" or path that leads into the muff from the cyl. It looks like the gas then hits the front wall and then spills into that outward chamber before it then finds its way out the muffler holes.

    I actually got a chance to look on ebay at those muffs. I think since i need a new one i may as well buy one of those that already has the extra holes in the muff. They look like the same price as the OE design if i buy a chineese part.

    Should i open up the holes on the example muffler that was linked to on this post or is that enough of an increase to do good? Im guessing that the cover plate on the new one needs to be opened up more if it comes with one, if it does not come with a new one i will grind out my old cover a bit more.
  13. MasterMech

    MasterMech Guest

    The new muffler will be a noticeable improvement but the MS390 will use all the extra breathing room you can give it.
  14. clemsonfor

    clemsonfor Minister of Fire

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    I don't want to go to big
    I ordered one similar to the link posted. But its from. A us seller and has the cover shield included. Its a few dollars cheaper also. It still has the 2 extra hole in it as well.Wat size should I make the extra holes?
  15. MasterMech

    MasterMech Guest

    Hard to do if you don't mess with the depressed rectangular area in the center. The mods that I posted are very conservative. Yields a great running saw that retains the muffler screen (IIRC you're a forester no?) and isn't appreciably louder than stock.

    IIRC I used a 3/16" drill to make those.
  16. clemsonfor

    clemsonfor Minister of Fire

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    I cant see the pic of your mods, its not coming up for some reason? I can see the pic of the pulled apart muffler were your showing me the shafts that the bolts go through ( and that is what the part i can see in there looks like through the tiny holes). I am a forester, but here on the east coast and in SC In the upstate forest fires are of little concern. This time of year you have to almost try and start a fire with matches and gas and if your successfull its far from a raging inferno, something you can almost run through is the result.

    Ok after saying that, i took the screen out of mine when i pulled the saw apart to fish out the decompression vavle from the cylinder. I figured it was just restricting it even more.
  17. MasterMech

    MasterMech Guest

    I fixed the post above.
  18. Joful

    Joful Minister of Fire

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    Reading this thread, I really need to do something to improve the power of my 036. The local Stihl dealer, whose business is largely based on saw repair and maintenance, says it runs great... so I guess it's giving all I can expect for a factory 036. But, it just feels very wimpy to me. Would a muffler mod make a real big difference with this saw?

    Come to think of it... my 064 is starting to feel wimpy, too. ::-) I was so impressed with this saw, the first few times out, but I guess our expectations grow with each hour of use.
  19. clemsonfor

    clemsonfor Minister of Fire

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    Yea the 036 will dobetter. The reason the 390 will do so well is that it has the exact same muffler as the 290 and 310 yet has to flow more exhaust, but they all will run better.


    To those that know can u refresh my mind on tuning this saw.

    Isn't it something like wide open till it starts 4 stroking or whatever then back off a half turn?
  20. MasterMech

    MasterMech Guest

    It's a bit more complicated than that. But the basics are to hold it at WOT and richer the H until it starts four-stroking and then back off until it cleans up. Then turn it back rich until it just begins to four stroke again. Saw should four-stroke when held open and clean up as soon as it touches the wood.
  21. pyroholic

    pyroholic Member

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    Can someone explain what 4 stroking is? I have a clear understanding of the true difference between a 4 stroke and 2 stroke, but not sure what 4 stroking is in a 2 stroke. How can you tell, and why does it do it?

    Phew, that was a lot of strokes in one post.
  22. Joful

    Joful Minister of Fire

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    You'll know it when you hear it. Basically, as you richen the H screw, you'll hear the saw go from clean to burble. There are some good (and some bad) videos on saw tuning on YouTube. Worth a watch before you start.
  23. MasterMech

    MasterMech Guest

  24. clemsonfor

    clemsonfor Minister of Fire

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    yep i found your post with that vid after i posted yesterday MM.

    What type tac is that?

    I have been wanting to buy one, i guess one of those with the wire that wraps around the plug wire will work you just are then connected and not wireless like the one you have looks like.

    Thanks for the picture fix. I see you have put 2 holes additional ontop of the 4 slots. i was thinking the factory only has 2 slots?
  25. MasterMech

    MasterMech Guest

    Stihl EDT-7, Can be used wirelessly, or comes with a wire lead and a clip that allows me to use both hands.


    Correct.

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