Bottom Bracket Coversion Kit

Discussion in 'Motorized Bicycle General Discussion' started by honda04rider, Apr 26, 2013.

  1. honda04rider

    honda04rider New Member

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    I have a single speed bike with coaster brakes. Why should I replace the 1 pc crank with the bb conversion kit? Do I need to buy new crank arms or am I still able to use them from the factory with the kit installed. Does the coaster breaks still work with the bb kit? Thanks for helping me understand.
     
  2. Nashville Kat

    Nashville Kat Active Member

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    What kind of motor do you have?
    Are you talking about wider cranks for a 4-stroke, or converting a one piece to 3 piece crank?
     
  3. honda04rider

    honda04rider New Member

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    Converting from a 1 pc to a 3 pc? Is it necessary or what is the advantage? I have the bearings and brackets.
     
  4. bigbutterbean

    bigbutterbean New Member

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    What nashville is asking is, do you have a 2 stroke or a 4 stroke? If you have a 2 stroke, you wouldn't need the bottom bracket conversion unless you are going to use a shift kit on a multi-speed bike. If you have a 4 stroke, you can either use the conversion kit or heat and bend your existing pedals, but the stock pedals will not clear the engine without modification. If you are using a 4 stroke and have the bottombracket conversion kit, you might as well use it. It's probably easier than bending your pedals.
     
  5. honda04rider

    honda04rider New Member

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    Thanks for the detail. I have a two stroke 66cc. The website I purchased from indicated if you had a 1 pc crank, you would need a bottom bracket conversion kit. So the 3 pc is merely to make the cranks wider? Does the 3pc affect the coaster break functionality?
     
  6. MotorBicycleRacing

    MotorBicycleRacing Active Member

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    The ~ 4 3/4" wide 66 cc 2 stroke motor fits between the vast majority
    of one piece cranks or 3 piece mountain bike type cranks with room to
    spare on both sides.
    There is no need to change anything.

    Do you have a link to that website?
    What kit did you buy?
    Thanks.

    One piece or 3pc cranks do not affect the coaster brake functionality.
     
    #6 MotorBicycleRacing, Apr 26, 2013
    Last edited: Apr 26, 2013
  7. honda04rider

    honda04rider New Member

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    TRUVATIV from pirate cycles. It came with two black brackets, the screws, and the bearings. The bicycle I purchased is a Micargi Rover GT that has a 1 pc crank.
     
  8. PAracer

    PAracer New Member

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    My current build is on a rover. There should not be a reason to swap to a different bottom bracket for a two stroke.

    I suggest building the bike with the existing cranks.
     
  9. honda04rider

    honda04rider New Member

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    Thanks PAracer, did you add a front brake, if so what kind... Or is the coaster break sufficient for you?
     
  10. Nashville Kat

    Nashville Kat Active Member

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    Um, if you are converting to a 3 piece crank, you obviously need the crank-

    It sounds to me as if someone gave you some bad info because a 2 stroke China Girl motor will fit between most normal cranks and axles both 1 and 3 piece- unless you have a pull start and centrifical clutch. You can get wider crank spindles for three piece setups- I think Sick Bikes sells some. Most 4 strokes need wider cranks.


    the advantage is that an alloy 3 speed crank generally weighs much less than a steel one piece crank-

    The weight difference may or may not be that important on a motorized bike- it is to me though and I have two builds both converted and with a single alloy sprocket on alloy 3 piece cranks.

    You can get a nice annodized single gear 3 piece alloy crank for about $40 and up- so with the conversion it's a little pricey- I use vintage cranks I got on ebay cheap.

    You can also go to a much smaller sprocket on your steel crank- even alloy-
    and a small gear not only gives an easy pedal, but can save a lot of chain link weight- to even difference between that and a 3 piece alloy set-up


    The conversion brackets like yours came along in the BMX days at the dawn of the 1980's- the three piece cranks are not only lighter, the bottom brackets have smaller and lighter bearings, except the older style which stilll use the one piece bearing sizes-

    If you have a 3 piece spindle you also have the option of using featherweight titanium crank bolts- I got some for about $10 a few years back, but maybe the prices are up- don't know.

    Can you post a link or links to your kit or the conversion kit? (Highlight the page address in your browser and copy it to clip, and then paste it in your post) That might make responses more accurate.
     
    #10 Nashville Kat, Apr 27, 2013
    Last edited: Apr 27, 2013
  11. PAracer

    PAracer New Member

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    My rover came with a springer fork. I added a caliper style brake using the mounting hole for the front fender. I did have to drop the fork a bit so that the calender could reach far enough. I would call what I have done to be the bare minimum. A drum or disc setup would be much better.
     

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