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Full Circle Cranks

Discussion in 'Chainsaw' started by Arrowhead, Mar 9, 2012.

  1. Arrowhead

    Arrowhead RARE BREED

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    I'm wanting to start building full circle cranks. What kind of filler material/epoxy should I use? Any pics, tips, suggestions would be appreciated.
     
  2. Modifiedmark

    Modifiedmark Tree Freak

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    I would use that blue polystyrene insulation because its light a Gorilla is cause its strong!
     
  3. Team FAST

    Team FAST ArboristSite Member

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    Billett steel. 4340 bar stock in normalized heat treat condition.
     
  4. Scooterbum

    Scooterbum Addicted to ArboristSite

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  5. Arrowhead

    Arrowhead RARE BREED

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    I was going to machine a solid ring to wrap around the weight. I'm not sure what to use as a filler.
     
  6. torence 20

    torence 20 ArboristSite Operative

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    maybe a dumb question but what would the advantage of doing this be? higher rpm?
     
  7. Jacob J.

    Jacob J. Tree Freak

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    Hey Ed-

    I got to check out a P-62 crankcase once that a guy had made a full-circle crank for, it was pretty trick.

    He used Superweld and it seemed to work fine. He said it resisted the fuel well.
     
  8. heimannm

    heimannm Addicted to ArboristSite

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    The full circle crankshaft occupies more volume in the crank case, which means as the piston goes up and down there is a greater pressure differential resulting in a bigger charge into the combustion chamber.

    I believe the old McCulloch's used epoxy of some sort, try looking through McBobaust's site McCulloch Chainsaws Downunder ................. for some information.

    Mark
     
    Last edited: Mar 9, 2012
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  9. CTYank

    CTYank Peripatetic Sawyer

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    Boosting crankcase compression ratio, while reducing crankshaft aerodynamic drag. What's not to like? (So long as it doesn't disintegrate.)
     
  10. Terry Syd

    Terry Syd Addicted to ArboristSite

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    Higher crankcase compression pushes the point of maximum delivery ratio of the transfers up higher in the rev range. Both the point of max torque and max horsepower end up higher in the revs.

    Here is a webpage with a graph to illustrate the concept, its down about halfway on the page -

    http://twowheelers.tripod.com/TTuning.html
     
  11. chainsawwhisperer

    chainsawwhisperer Addicted to ArboristSite

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    I built a full cycle crank for a 10-10. I did it only as an experament to see if it would hold together, The saw was not ported. I used hardpaper as the backing and the ring around the crank, filled the whole works with epoxy then turned the crank down to the counterweight diameter and faced it to the width of the counterweights.
    Not only did it hold together, It seemed to shift the operating rpm up a bit.
    Jim
     
  12. Terry Syd

    Terry Syd Addicted to ArboristSite

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    I read one post (can't remember where) that the mod bumped the rev range up about 400 rpm on one person's chain saw.
     
  13. rupedoggy

    rupedoggy Addicted to ArboristSite

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    Does the 357 Husky come from the factory with a full circle crank?
     
  14. ndlawrence

    ndlawrence ArboristSite.com Sponsor

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    It comes with crank stuffers.
     
  15. husq2100

    husq2100 Addicted to ArboristSite

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    So does the K960, 372XT, and I think the new K970..... Here are a couple I have to fill:

    [​IMG]
     
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  16. husq2100

    husq2100 Addicted to ArboristSite

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  17. husq2100

    husq2100 Addicted to ArboristSite

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    If it is possible to "bolt in" a 372 XT crank in a 372 XP, I would love to see a side by side comparison. That would mean, say for ease, to cases set up with oilers etc, But I would say to use the same cylinder, piston , intake, carb and muffler...all to lesson the difference in production tollerances.
     
  18. tree monkey

    tree monkey Addicted to ArboristSite

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    [video]http://i155.photobucket.com/albums/s294/scottk66/dadssawparts001.jpg[/video]
    autobody filler marglass
     
  19. logging22

    logging22 Cuttin to live, livin to cut

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    How about balance? If the filler material is a different density, would that throw off the balance?
     
  20. gink595

    gink595 Banned

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    I've got a P5000 crank that was stuffed, haven't tried it out but I have a P5000 cylinder coming from Canada. The crank was done by Marcel Vincent, I will be curious to try it.
     

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