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372 chain tension problem

Discussion in 'Chainsaw' started by ThackMan, Jan 8, 2019.

  1. ThackMan

    ThackMan ArboristSite Operative

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    I have a 365 pre xtorq with a 372 cylinder on it. The saw runs great. However when sharpening the chain one day I noticed that the chain tension changes when rotated by hand. The bar is new and the tip appears to run true. Could I have a defective rim sprocket? This seems to happen regardless of crank position, so I’m thinking that it wouldn’t be a bad crank.


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  2. HarleyT

    HarleyT Tree Freak

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    Put up a pic of the sprocket and bottom side of the chain.
     
  3. vortec325

    vortec325 ArboristSite Operative

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    New chain ? Any links move stuff ? How much does the tension change ? I’ve noticed with a new sprocket it will be kinda “notchy” and a brand new bar will be “notchy” too . I’d run a tank of gas threw it before I started looking for issues


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  4. Mauser

    Mauser ArboristSite Member

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    If the motor is not moving around in the case, the only thing that could cause your problem is having something out of round or a chain link that is not moving freely (this assumes you have the correct pitch chain for the sprockets and no damaged drive links dragging in the bar). I'd start by finding the tightest point, then marking a spot on both the sprocket and the tip sprocket. Then carefully move the chain forward until you hit the tight point again and re-check those two sprocket marks. Since they are different sizes, they will not rotate equally, and if one shows your mark in the same spot it was at the first tight point, you have found your problem. Of course, that tight point should be repeatable with every turn of the suspect sprocket to the same position.

    If it indicates the rim sprocket, then I would pull it off and move it 180 degrees to repeat the test. If the marked spot continues to be at the same place for each tight point in the chain, then it confirms the sprocket, but if it is now reversed, then the problem is with the output shaft. or clutch drum. Of course, since the output shaft is not turning at all when you manually move the chain, that makes it HIGHLY unlikely that it could be the issue. But the clutch drum COULD be the problem, and that would be shown by moving the rim sprocket on the drum.
     
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  5. ThackMan

    ThackMan ArboristSite Operative

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    It’s a new chain 24” Stihl rs. I’ve run 3 tanks through the saw on this bar and chain combo. And it goes from snug to 1/4”-3/8” slack. It’s weird. I was kinda thinking of throwing a fresh rim sprocket at it.


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  6. ThackMan

    ThackMan ArboristSite Operative

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    The thing is it doesn’t change regardless of crank position.


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  7. vortec325

    vortec325 ArboristSite Operative

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    Yah should be good by now . I’d start by checkin the chain for bad links . Maybe throw up a pic of the sprocket . I put a brand new sprocket , chain and bar on mine . I still have a little variation in tension . I think that’s nature of a new sprocket . If I put a well worn on it runs smooth as silk .


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  8. Mauser

    Mauser ArboristSite Member

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    If it is a new bar AND a new chain, that implies you have an old one of each. Have you tried re-mounting the old parts and repeating the test?
     
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  9. Mauser

    Mauser ArboristSite Member

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    You have said that twice now, but I really have no idea what you mean.

    It implies that you have done something like the test I described, and the point on the rim sprocket is in a different place at each tight point of the chain. If this is the case, then your problem CANNOT be the rim sprocket (or that you have more than one thing causing the problem, such as TWO sprockets, both slightly out of round, and the issue is only obvious when they both "sync" to the same spot).

    How did you test the crank position? The only thing I can think of is to position the chain to a loose point and then manually turn the crank to verify that it did not affect the tension.
     
  10. old guy

    old guy Addicted to ArboristSite

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    Have you looked at the clutch bearing?
     
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  11. Jacob J.

    Jacob J. Tree Freak

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    Bent tensioner screw, worn rim sprocket, worn clutch drum, or as mentioned above - bad clutch drum bearing: any of those factors will cause chain tension problems if your bar and chain are new and have been ruled out.
     
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  12. 67L36Driver

    67L36Driver Tree Freak

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    Is ALL the chain links new and the same brand?

    I had one do the classics tight/loose action and it was actually 58 drivers of used Stihl chain with 14 drivers of new Oregon added to fit a 20” bar.

     
  13. HarleyT

    HarleyT Tree Freak

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    Put up a pic of the sprocket and the bottom side of the chain {if you have run the chain on this old worn out sprocket}..
     
  14. HarleyT

    HarleyT Tree Freak

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    I assume your phone has a camera.
     
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  15. grizz55chev

    grizz55chev Addicted to ArboristSite

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    It says I phone, so yep!:cool:
     
  16. ThackMan

    ThackMan ArboristSite Operative

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    [​IMG]


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  17. ThackMan

    ThackMan ArboristSite Operative

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    [​IMG]


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  18. ThackMan

    ThackMan ArboristSite Operative

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    [​IMG]


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  19. ThackMan

    ThackMan ArboristSite Operative

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    [​IMG]


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  20. vortec325

    vortec325 ArboristSite Operative

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    I’m use to the stihl rim sprockets but that looks severely worn


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