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BBSxx Drive will not slide through bottom bracket

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    BBSxx Drive will not slide through bottom bracket

    Nothing is more frustrating than hitting a problem out of the blue. When building an eBike kit you have to expect some level of problems and things you are going to have to work out or around. That's just part of the bike building experience, even non powered bikes.

    You know the scenario, your ready to start the project, you have gotten all the parts you need , you are working along then WHAM something you didn't even think about being a problem , is. That happens with bottom brackets more often than you might realize. This article serves as your warning that this might happen.

    You try and insert the motor shaft through the BB and it just won't go. A little twisting and pushing may help , but a properly fitted motor does not need any extra force or twisting to pass through. The likely suspect is a bottom bracket intrusion. When frame makers put the BB shell into the jig for welding there are holes in it where the tubes will intersect. Some manufacturers use guides that fit into the hole and keep the tube aligned until the welding has completed, those guides stay in the frame forever. The piece of the guide that fits into the hole in the side of the shell sometimes pokes through a little. This is not a big deal for a traditional BB since many are narrowed in the center . The BBSxx motor shaft is a constant diameter all the way and anything sticking into the shell could be a problem.

    You can see in the photo below there is a ridge of the guide protruding into the BB shell.
    Click image for larger version

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    The solution is as simple as you may have guessed. Grind it away.

    I used a Dremel tool with a ¾" sanding drum. Just be careful not to mess up the threads or you will have issues if you ever want to put a traditional bottom bracket back in. I simply sanded the entire diameter of the center section until I could no longer feel the intrusion.
    . Click image for larger version

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    You can see in the above photo, the freshly sanded diameter. Clean out the metal dust thoroughly from the center section and the threads. I used a dry shop rag followed by a paper towel damped with rubbing alcohol. Once that had dried a light spray and a wipe with some Boeshield T-9 for corrosion resistance, you can use whatever brand you like.

    Insert the motor shaft and you are on to determining chainline and chainstay clearances.
    . Click image for larger version

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    Last edited by Bicycle365; 07-19-2016, 06:31 PM.

    WOW!! There's a spacer gobbling build! Good post, a not uncommon build glitch! Love that Dremel! Boeshield T-9 or ACF50 should be in EVERY eBike kit. Best corrosion and protection for electric bits as well. Good enough for aerospace, good enough for eBikes.