Extreme engine vibrations at higher rpm's...

Discussion in 'Motorized Bicycle General Discussion' started by borntofli, Oct 10, 2012.

  1. borntofli

    borntofli Member

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    With the clutch pulled in and revving it up, anything past mid rpm's produces severe vibration-shaking...... Runs fine at lower rpm's, but above mid point the shaking becomes unbearable.....

    Driving down the road, smooth till 21 mph... after that the vibration escalates that I never go past 23 for fear of blowing it up...

    Which internal part is wearing out and causing this???

    I have about 5-600 miles on the engine...

    HT 66

    amsoil 50:1
     
  2. littletinman

    littletinman New Member

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    What size back wheel sprocket are you using?

    this is most likely, from my understanding, due to crank balancing issues.
     
  3. borntofli

    borntofli Member

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    39 tooth sprocket.......
     
  4. borntofli

    borntofli Member

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    On my ride to work today, i'm only able to go 18-19mph due to severe vibrations above that....It seems to be getting worse....

    Revving in neutral, its good till approx 4000rpm and from 4-6000 severe vibration and a different exhaust sound...kind of like an exhaust leak, but not exactly....above 6000 it smooths out...

    I'm waiting for it to explode.....

    It definately doesnt have the same power it had....

    I'll be ordering a new engine today, and when I get it on I will fix this one if I can figure out what is wrong.....

    Any ideas???
     
  5. littletinman

    littletinman New Member

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    Could be the bearings. Mine did that when my bearings were going. What brand is the engine?
     
  6. borntofli

    borntofli Member

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    boy go fast....
     
  7. littletinman

    littletinman New Member

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    I had all my bearings go on my BGF engine. I'm betting it is that.
     
  8. borntofli

    borntofli Member

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    Is it the needle bearing engine that i want to get to replace this one????
     
  9. littletinman

    littletinman New Member

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    It's the four 6202 bearings. Two are on either side of the clutch shaft, and two are on either side of the crank weight "wheels". You'll have to take the engine completely apart to service them.
     
  10. 2door

    2door Moderator
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    Question: Why are you reving to max rpm with the clutch disengaged? Would you do that to your car's engine, or a motorcycle, or a lawn mower? If there is a problem you're sure to find it eventually by over reving the engine. If there is no problem there will be soon.

    Tom
     
  11. JonnyR

    JonnyR New Member

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    if its just the wrist pin bearing its not to hard to chainge if its the crank bearing you need to take everything apart
     
  12. borntofli

    borntofli Member

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    I went ahead and ordered a new engine.... This is my only form of transportation so need to get it going quick.....

    Will be interesting to see what went wrong......
     
  13. JonnyR

    JonnyR New Member

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    my wrist pin bearing was do ing the same thing im im the prosses of doing it its hard to get myself to do it though i have the replacement out of another fail of a engine soaking now
     
  14. littletinman

    littletinman New Member

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    I just rebuilt my BGF engine twice two weeks ago. So everything's fresh in my mind if you need some help or suggestions.

    I'm in pretty much the same boat as you. I have two engines. Both almost exactly the same. When one breaks, I swap it for the other, and vice versa. Adds a bit or reliability to the hobby.
     
  15. JonnyR

    JonnyR New Member

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    im trying to collect the parts for a 4 stroke bike now so this one can be for fun and trying out forum things like porting and such
     
  16. borntofli

    borntofli Member

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    When I start to take it apart, how would I tell if the wrist pin bearing is bad before i take it all apart????
     
  17. JonnyR

    JonnyR New Member

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    if the piston moves around on the rod if it jiggles and moves up and down with out the rod moving
     
  18. borntofli

    borntofli Member

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    I hate to admit this but I fixed te problem w/ the vibrating.....I'm calling myself an idiot so feel free to do the same.....

    It turn out that my front motor mount stud was lose.... I know I checked all mounting connections, but somehow I missed this.....

    Got it tight and all problems are gone... I guess the shaking was foaming the gas in the carb and causing all kinds of symptoms.....

    Finally found the right size o-ring for the intake and now it runs so smooth.....

    Can't wait to get my pipe back on and I will have dirtbike like performance again....

    Thanks all for all your help, I now have a new engine coming that I dont need...Guess i'll just have to build another bike....
     
  19. borntofli

    borntofli Member

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    Put my new engine on and It went smooth..... Only difference was thhat the exhayst port angle is just a bit different than my old engine...

    Had to do a little grinding on my front mount for the exhaust to clear....

    New engine runs well, idles great....

    Now to tear down the old one and see which gasket is leaking......Who has the best head and base gaskets????
     

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