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372 crank mod

Discussion in 'Saw Building 101' started by Matto, Mar 12, 2017.

  1. Matto

    Matto ArboristSite Member

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    Hi guys,

    I'm preparing for a full engine tune up, case, porting and piping, ignition, on a husq 372XP.

    I have been looking for, and I don't know the specific term in english, a crank with full mass or volume. I didn't find anything on the web. Maybe one of you know if they exist?
    This is what I mean:

    IMG_0763.JPG

    If it doesn't exist I will make one myself on the base of an OEM one and filling the missing volume with resin.

    Thanks
     
  2. mdavlee

    mdavlee Tree Freak

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    Full circle. You'll have to make one for a 372
     
    Big Block likes this.
  3. Matto

    Matto ArboristSite Member

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    Thanks! In french it's ´vilebrequin à masse pleine ´ for all you want to know :reading: ;)
     
  4. ironman_gq

    ironman_gq Addicted to ArboristSite

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    I'd be a little concerned with resin coming loose at high RPM and ventilating the crank case.
     
  5. harpersend

    harpersend ArboristSite Lurker

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    Some folks just call them crank stuffers...

    I wonder if you could lighten the crank with strategically placed holes and use those to help keep the resin attached to the crank...
     
  6. MANesler

    MANesler ArboristSite Member

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    Also heard them called stuffer cranks.I know they are avalible for atv And diet bikes. But does anyone make them for chainsaws?
     
  7. bowenp

    bowenp New Member

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    I noticed the 562XP has "cups" on the crankshaft effectively factory crank stuffers. Has anyone tried them on a 371-372 crank?
     
  8. Jacob J.

    Jacob J. Tree Freak

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    The 372XT has them from the factory.
     
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  9. trappermike

    trappermike ArboristSite Guru

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    The Japanese first used "Full Circle" cranks in their motorcycles from the '60's and on. To balance the cranks the counterwieghts each have 2 large holes thru them on each side of the big end rod pin,to remove wieght there to compensate for the heavy rod and piston assembly on that side. The full circle counterwieghts "Fill" the crankcase more and raise the crankcase compression ratio for more power over the old fashion "porkchop" cranks,which chainsaws still use today! To make the full circle cranks even better modders would "stuff" the counterwieght holes(with cork and epoxy) to raise compression even higher. My favorite motorcycle engine to mod was the only factory 2-stroke ever to have the holes already stuffed by the factory,and thus for 3 years it was the fastest production motorcycle made.
    I did design and build a few full circle(and stuffed) stroker cranks made of titanium for hotsaws(they were a few grams lighter than a stock porkchop crank),but that is one hell of an undertaking even made with steel! Also I had to do a lot of research to figure out how to get them in the same "semblance" of balance as factory.
    I proved it was possible but it's a daunting task and expensive and a expert machinist is not cheap. I consider it the very last mod you can make to a full out competition saw in the search for the last ounces of power but not practical for anything less.
     
  10. trappermike

    trappermike ArboristSite Guru

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    I still have the original blueprints I made for the full circle 2mm stroker crank in my archives,they can be made of steel instead of titanium also. I aslo cc'd the crankcase with the stock,and then modified crank to find out the crankcase compression ratio of both,the full circle crank raised it quite a bit. I do have 2 photos of the crank,however the light setting on my bosses camera was wrong and the photos are a little dark...
     

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