Balanced Crank?

Discussion in 'Performance Mods' started by Dave FZ1000, Mar 17, 2018.

  1. Dave FZ1000

    Dave FZ1000 New Member

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    Know of anyone who Balances Cranks, or sells them? Seems the balanced cranks I read about are old ones, or from companies that seem to be out of business. Seems like a worth while mod to me, especially since it would help protect the engine and other parts as well, at least. Doubt it's something I could do with minimal equipment. Thanks for any ideas, etc. I'm kind of new to this.
     

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  2. FurryOnTheInside

    FurryOnTheInside Well-Known Member

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    My interpretation is when we say "balanced crank" this just means the best balance of piston, con rod and crank counterweight that we can get for our own peak RPM.

    You can get a better balanced (than a stock generic) engine using very minimal tools. :)
    It is definitely a worthwhile mod. The early posts on this forum are full of stories about bolts falling out, frames cracking from metal fatigue, and people needing foam grips and springs under the saddle to stay comfortable.


    Personally, I started by drilling a couple of holes, one in each crank cheek. Radially drilled, so no need to split the case. Starting with a 3/16" tungsten carbide bit and then used a 3/8" tungsten carbide bit. Drilled about 15mm deep measured nearer the side of the hole than the middle so it is the average depth (you can drill shallower then go back and drill deeper later on if you wanted to).
    I then lightened the upper half of the connecting rod somewhat just by grinding a bit of material from around the edges using the grit stone whatsit on the Dremel. I haven't seen any posts about bent con rods so I assumed there is some excess material, and removing steel makes sense for lowering weight.
    I did remove quite a bit of aluminium from inside the piston skirt using a tungsten carbide burr in the Dremel, but it's a less dense metal. I haven't seen any bent piston skirts so I assumed that there's excess material there too (and also the fact that there are thinner and thicker bit of the skirt so I think it can all be a thin as the thinnest part).

    I have VERY little vibration up to 7000 RPM and not excessive vibration up to 8000 RPM (which is the highest RPM I've tried).

     
    Last edited: Mar 17, 2018
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  3. Dave FZ1000

    Dave FZ1000 New Member

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    YES! What a great answer, right off the bat! So, looks like I can do a little after all. Was wondering the other day about lightening the piston too, though I hadn't heard of it having been done. Think I'll do a little of those mods on my new 49cc kit, which should be delivered Monday. Not going to go overboard on anything. Not trying to make a racer or anything like that. Just hoping to make a more efficient, longer lasting engine, perhaps with even a little better mileage. Thanks so much Furry...! I did attempt searching posts, just didn't seem to see what I was looking for. Oh, photos were Very Helpful too!
     
  4. FurryOnTheInside

    FurryOnTheInside Well-Known Member

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    Well, I have to thank Jaguar for his posts here on the forum and his wonderful dragonfly75.com site which enabled me to only do the balance jobs once, no experimenting at all, because his figures worked so well for me. :)
    http://www.dragonfly75.com/motorbike/
     
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  5. Dave FZ1000

    Dave FZ1000 New Member

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    Great again! Checked out a site just a little so far. Can see I'll be spending some time there in the future too. Thanks again!
     
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