What size bottom bracket is Cranebrook 56387

Discussion in 'Motorized Bicycle General Discussion' started by Nehmo, Jul 25, 2017.

  1. Nehmo

    Nehmo Member

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    I'm installing a 4-stroke motor (of no brand name but probably common) on a Cranbrook 56387.
    Everything is attached, except the original one-piece crank & front sprocket is too narrow. The kit comes with a couple of wide cranks that have the square hole. crank20170725_105548.jpg [​IMG]
    What size and type bottom bracket insert do I need to install this wide crank?
    Can anybody recommend something?
    Apparently, I need something with the square peg coming out.
     
  2. malatious

    malatious Member

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  3. Nehmo

    Nehmo Member

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    The description for that BB conversion kit gives 3 cup sizes. When I order, do I choose a size, or does it come with all 3?
    Do I need to measure the existing cup socket?
    I emailed Kingsmotorbikes.com with the same question.
     
  4. kevyleven007

    kevyleven007 Active Member

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    I think it has to do with how much space is between the cups on your frame. Check youtube for some help.
     
  5. malatious

    malatious Member

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    I didn't even notice that it shows 3 different cup sizes, but it gives you no option when you order it. I have put this item on 2 different frames and it has fit fine. One was a Huffy Cranbrook, and the other was a vintage style Roadmaster frame. Just make sure to use Locktite and torque the crank nuts down good or they will come loose when you are riding.
     
  6. Nehmo

    Nehmo Member

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    20170802_034111.jpg 20170802_034006.jpg We got the bottom bracket replacement from Bike Berry. It was cheaper from them because their shipping wasn't as much. The bearing holders were a bit bent, but they could be bent back into shape. And, actually, they are the same as the bearings in the original bike. The collar on the replacement bottom bracket shaft goes on the left.
    I soon realized the pedal shaft size is different on the new crank arrangement. I had to get some pedals off a junk bike I had. The new pedals have a 9/16" shaft. The ones on the Cranbrook are 1/2".

    Nonetheless, the new cranks didn't quite clear the motor. The pics show the left side from the back. I filed a little on the case of the centrifugal clutch. In one pic, the crank is in the up position. It looks like it's touching, but it's not.
    I could have moved the motor a bit, I suppose.
    Now, I'm working on the chain running smoothly. It clicks occasionally when it slightly misses a tooth on the driven sprocket. I think I need to align the rag sprocket better.
     

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