No more vibrations (almost)

Discussion in 'Motorized Bicycle General Discussion' started by msrfan, Sep 30, 2010.

  1. msrfan

    msrfan Active Member

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    I was plagued by vibrations a few weeks ago with 2 bgf motors in a70's-80'scruiser. A third bgf went into a Panama Jack and it's livable (photos forthcoming). So, I was on the verge of sending the crank away to be balanced. After studying the formulas on line and visiting a friend with an automotive machine shop, I concluded that I could do the job myself. I really didn't want to split the crank so I used the same formula but utilized the conrod as part of the bobweight. Now the motor revs high and vibrate's little at max rpms. Very rideable. I had to take off considerable weight at the rod pin. Also I didn't have to use the head or muffler brace. I want to thank all who responded to my first thread with some great suggestions.
     
  2. Dan

    Dan Staff
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    Sounds awesome and looking forward to your pics.
     
  3. msrfan

    msrfan Active Member

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    Okay, finally posted photos of my balancing job. First I weighed the small end of the level conrod, then the piston assembly and added the two weights together. Divide by two, subtract the weight of the small end of the rod and the total is the magic number you have to add to the hanging rod so it can be properly balanced. I used solder of that exact weight and wound it around the rod. The crank assembly on the levelled rails will settle into a heavy spot in which you remove metal until it has no more heavy areas. The two things making this possible without splitting the crank are that the rod is on a needle bearing and hangs down no matter the position of the crank keeping the weight on the rod pin, and the fact that the piston assembly is enough heavier than the rod that you must add weight to the rod instead of subtracting. As soon as you get your weight measurements, you must forget about the rod as being a rod and consider it part of the bobweight. The motor ran nice and smooth with only a hint of vibration at the highest rpms, mostly noise and still very rideable. I have at least one more motor to balance and I will post my results.

    [​IMG][​IMG][​IMG][​IMG]
     
    #3 msrfan, Oct 9, 2010
    Last edited: Feb 27, 2017
  4. ProDigit

    ProDigit New Member

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    Nice, however not an option for many of us, who don't have the access, money, or tools to do this.
     
  5. mountain80

    mountain80 New Member

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    I did mine at home with a set of 10 dollar v blocks , a small food scale simialar to the one depicted and a cordless drill, swingin 7100 rpm smoothly now scared to let er go further but I have 2 more balanced cranks in stock just in case lol.
     
  6. msrfan

    msrfan Active Member

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    Sounds economical enough to me.
     
  7. ProDigit

    ProDigit New Member

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    Are there places where you can buy those rubber V-blocks, and mounts?
     
  8. msrfan

    msrfan Active Member

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    You can use just about any 2 thin strips of metal, plastic or even wood. Mount them on a block of wood and make sure they're parallel and level. Mine is made of aluminum angle with leveling screws at each corner. The scale was around $10.00 on ebay. Solder can be purchased at most auto parts stores or you could even use clay. Any drill motor with bits or even a grinder can be used to remove weight from the heavy side.
     
    #8 msrfan, Apr 3, 2013
    Last edited: Feb 27, 2017
  9. donphantasmo

    donphantasmo Member

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    OK. This really intruiges me. But, can you re-type that again?

    I got lost in there. If it is at all possible for someone to Youtube a video, I'd be very very happy.

    So, you removed metal from the crank, untill it was level (no heavy setteling), with the connecting rod + the weight added on to it?

    Help me out. I'm probably going to do this this weekend.

    Thanks
     
  10. msrfan

    msrfan Active Member

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    The formula that worked for me is to weigh the small end of the level conrod and add that to the weight of the piston assembly, then divide by 2 and subtract the weight of the small end of the level conrod you weighed earlier. Take that number and match it with some solder. Wrap the solder around the rod and put the crank pins on some homemade level, parallel rails. It will roll and settle with the heaviest side down. Remove material from the heavy side until it will roll and stop at different places every time, showing it has no heavier spot. The heavy spot may change a little as you go, so you have to adjust your material removal accordingly. I encourage you to make a youtube video as I don't have a motor to balance at this time. Good luck and let us know how it goes.
     
    #10 msrfan, Apr 4, 2013
    Last edited: Feb 27, 2017
  11. donphantasmo

    donphantasmo Member

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    Thanks, msrfan.

    I'll try that on my spare engine, first.

    Cheers
     

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