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Centring the flywheel

Discussion in 'Chainsaw' started by Farmerboy, Sep 13, 2019.

  1. Farmerboy

    Farmerboy ArboristSite Member

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    Have a question guys. How important is it to exactly centre the flywheel in the case? What if it’s a bit off centre (although though to measure precisely). This is 372xp
     
  2. grizz55chev

    grizz55chev Tree Freak

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    I’m assuming you mean the crankshaft?
     
  3. Mad Professor

    Mad Professor Addicted to ArboristSite

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    You want it centered. Perfect

    A member here, Pioneerguy600, has a great method.

    Put a little valve lapping compound on the inside of flywheel /crank. Slowly lap by turning the flywheel, to lap the surfaces. Clean up very well, lapping compound is abrasive. Fit will be perfect.

    PG600 will chime in if I'm wrong.

    The crank actually centers flywheel.
     
  4. Mad Professor

    Mad Professor Addicted to ArboristSite

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    That's another matter. Left/right or bearings in cases..........
     
  5. Farmerboy

    Farmerboy ArboristSite Member

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    Case is tightened up. Will I be able to move it with a mallet?
     
  6. grizz55chev

    grizz55chev Tree Freak

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    A light smack with a dead blow hammer will do the job. Brass hammer works, take care to not damage the threads.
     
  7. Mad Professor

    Mad Professor Addicted to ArboristSite

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    You mean center crank, left/right.

    Usually a soft headed mallet will work. Make sue nothing rubs and all turns freely.
     
  8. Farmerboy

    Farmerboy ArboristSite Member

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    Yes, centre the crank left / right. It does turn freely, but am wondering if it needed to be centred exact
     
  9. farmguywithasaw

    farmguywithasaw ArboristSite Operative

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    The closer the better the the force on the crank is straight up and down
     
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  10. Huskybill

    Huskybill Addicted to ArboristSite

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    Once the case is assembled then center the crank in the case. This can bow the crank weights a tad, I put the rod at bdc and use a cold chisel to put the weights even again. Just a light shot will do it .
    I’d the crank is tight in the case after assemble after you centered it try this method.

    It works on the older husky dirtbikes too.
     
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  11. alexcagle

    alexcagle Cutoff Saw Specialist

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    I put a bolt that is lightly wedged and centered between the counterweights.
    Some cranks can get bent easier than you'd think.
    Then you've got a wobble that eats the bearing pockets at 13,000 RPM until the bearings are loose in the case. NO BUENO..
    Happens a lot to K760's on the clutch side, from other tools being thrown into the truck on top of the saw at "Miller Time".
     
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  12. Farmerboy

    Farmerboy ArboristSite Member

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    Sorry if I’ve not been clear. It’s the counterweights that aren’t centred in the case. Haven’t been able to move with a mallet.
     
  13. Cantdog

    Cantdog Tree Freak

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    Yep that wasn't clear in the first post as you were asking about the flywheel not the crankshaft. It's generally best if the counter weights are close to centered in the assembled cases. However......the piston centers the con rod on the big end bearing......this figure varies wildly depending on the performance level of the stock saw. I other words the amount slop between the top of the con rod and the wristpin bosses affects how the entire lower end is established. Generally the lower performance saws have a large amount of play between the side of the upper con rod and the piston boss which means the rod can move left and right a lot........as performance increases this measurement will decrease. The difference I'm describing is like from 0.010 on a good performing saw to up to 0.200 on a cheap low power saw. What I'm coming to is.....the more high performance your saw the closer to center your crank should be so that the lower end of the con rod is not rubbing on the sides of the counter weights........and again this is controlled by the piston.....and the piston only...
     
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