Can this work (crank balancing sorta)

Discussion in 'Motorized Bicycle General Discussion' started by junked, Sep 2, 2010.

  1. junked

    junked New Member

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    Here's the deal. I can't split my cases because I had to weld the crankshaft gear to the crank. (long story) Anyways, this engine runs very well but has severe vibration towards the higher RPM range. So, let's say I pull the jug and piston and have access to the crank counter weights. I was thinking of drilling out some material on the crank pin side of the counterweights. Doing this purely as guess work, what do you think the result might be? I know this is completely unorthodox, but the vibes keep me at about 15 mph or so. If I am consevative on the drilling, it might improve assuming that is where the weight needs to be reduced. Call me crazy.
     
  2. GoFastBicycles

    GoFastBicycles New Member

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    Go for it ...You have nothing to loose. Crazy

    Adam
     
  3. killercanuck

    killercanuck New Member

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    Could be worth a shot, but you're sure your mounts are super solid? Make sure you don't leave any shavings around :p
     
  4. foureasy

    foureasy New Member

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    your motor is junked
     
  5. junked

    junked New Member

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    Yes, the mounts are good and rigid. I figured I would put a lot of grease where I drill to catch the bulk of the shavings, and then flush it with a garden hose holding the engine up side down.
     
  6. junked

    junked New Member

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    No, I'm junked.
     
  7. Kevlarr

    Kevlarr New Member

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    Going to be hard to actually balance since you only have access to one side of the crank. I pretty much did what you're thinking of on my crank, just made a few divots on the crank weights with a 1/2" bit. Not a true "balance" but it helped me get past my 31mph wall.
     
  8. junked

    junked New Member

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    I planned on not splitting the cases at all, and drilling vertically into the crank weights. :/
     
  9. killercanuck

    killercanuck New Member

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    lol, care to elaborate on the welded crankshaft gear? It does sound like a good plan, even if only one side of the crank is drilled. That's a great idea about the divots Kevlarr! How much did you take off? Have a pic? :)
     
  10. Kevlarr

    Kevlarr New Member

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    Didn't take any pics, wanted to be able to deny everything if it wound up being a catastrophic failure, but there are plenty in other crank balancing threads. I just followed them up to the point of actually weighing everything. rotfl

    Often wondered though, what would happen if someone were to drastically lighten the crank weights, kind of like running a car engine with a lightened flywheel and harmonic.
     
  11. kipharley

    kipharley New Member

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    I wouldn't want that thing between my legs when it desides to grenade!
    How about a video of the first ride after you get it back together.
    Hey maybe we should start a pool to see how far it goes before it goes balistic.
    Or start a fund for medical bills!
     
  12. junked

    junked New Member

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    That's not going to happen. I am not going for perfect balance, I just want to try and move the vibration up higher in the rpm range. A little bit can make a big difference. If it gets worse, not better, oh well. It is more likely to grenade the way it is. I will document what I do. You won't see any blood.
     
  13. corgi1

    corgi1 New Member

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    If you look at the different crankshaft balance threads and talk to one of the guys that has balanced a lot of these cranks,he may be able too tell you the general position too drill and amount too remove (if they all need balancing)
    good luck
     
  14. junked

    junked New Member

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    Here is what I did. I'll try it this morning and ses if it made a difference.
     

    Attached Files:

  15. junked

    junked New Member

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    Wow, what a difference! I can now cruise at a perfect speed smooth as silk. I did this based on assumptions and guess work, and it paid off.

    Gone cruising.
     
  16. killercanuck

    killercanuck New Member

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    Right on man! Thanks for the pic! I'll have to try that too!

    Cruise on!
     
  17. foureasy

    foureasy New Member

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    nice work dude. the more you remove, the higher the sweet spot will be. the only problem with balancing that way is that you lose some of your "primary" or "crankcase" compression, which is the ratio of the crankcase volume with the piston at tdc to the volume at bdc. up to a.certain point, more is better. you aren't anywhere near too much though. on your next motor, (with a removeable crank gear hopefully) you should remove the weights and remove material from the instead, then you can fill the empty spots in the weights with silicone and assemble.
    what a difference though huh
     
  18. kipharley

    kipharley New Member

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    WOW.Good for you.I would of thought it would of eaten itself up!
    Glad it worked out for you,without you loosing any body parts!
    Thanks for documenting your "experiment".
     
  19. killercanuck

    killercanuck New Member

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    cool foureasy, I never though of the bottom end volume effect, does silicone even hold at high rpm? I guess drill a little deeper to counter the weight of the sili/goop, eh?

    My engine just had a chill run through it :D Heh heh.
     
  20. junked

    junked New Member

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    I rode about 40 miles today and it is like having a new engine. A word of caution though. The only thing I was worried about by doing this, was keeping the drill shavings out of the bottom end. I strapped the engine to the underside of a fork on a forklift, and raised it above me so that I could drill it upside down. Gravity is very helpful in this. I also sprayed white lithium grease on the crank so that it would catch any stray shavings. When I was done drilling I sprayed it with Gunk and flushed it thoroughly with a garden hose. All of this was done in the upside down position.

    Next time, I will do it the right way as Foureasy does it. But keep in mind I only tried this because I could not split the cases. Glad I did it though. : )
     

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