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Press Fit & eccentric Bottom Brackets, Carbon frame and Bafang Mid-Drive Kits

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    Press Fit & eccentric Bottom Brackets, Carbon frame and Bafang Mid-Drive Kits

    If you are planning to build a mid-drive BBSxx series bike, then the first piece of information you need is what size and type bottom bracket shell you have.

    Full article on choosing a BBSxx kit here

    The Bafang BBSxx series of motors is designed to replace standard JIS-BSA threaded bottom brackets. If your bike does not have that style you might still be able to install one using an adaptor. Basically an adaptor takes the (larger diameter) bottom bracket shell and converts it to JIS-BSA.

    What bottom bracket do I have ?
    Well, let's find out.

    Using the correct tools , remove the existing botton bracket. This job might be left to a local bike shop if you do not have the tools, patience or know how to do it yourself. Some bottom brackets can be very stubborn to remove, even if the bike is brand new.

    What you are looking for is the width of the BB shell and the inside diameter of the shell.
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    Now that you have those measurements you can determine what BB style you have.

    The three styles that adaptors are available for are :
    This standard was designed to allow a larger crank spindle diameter so to add that space the bottom bracket shell was enlarged to a 42mm diameter.
    PF30 (see special notes below)
    This was intended to further strengthen the BB30 standard so set the BB30 bearings into a press fit cup, to add that space the bottom bracket shell was enlarged again to a 46mm diameter.
    This is much like a PF30, it uses bearing cups , but PF41 uses standard bottom bracket bearings instead of BB30 sized bearings. The result is a bottom braket shell that is 41mm in diameter.

    Special note on CARBON FRAME BIKES, ECCENTRIC BB and all the bikes that uses a bottom bracket adaptor** Huge thanks to @Sebz for the following important info I originally omitted**

    The outside diameter of the spindle on a BBSxx is about 33.6mm in order to fit through a JIS-BSA BB shell. For Example the PF30 outside diameter is 46mm. That means that the adaptor is about 6mm thick, to that you need to add the thickness of your BB shell (frame). If your shell is 5mm thick (most carbon frames are more) then you have used 11 mm from the edge of the "hole" to the outside of your BB. The BBSxx only has about 12mm between the motor casing and the spindle so this will be a VERY tight fit with little room for error or sloppy measurements. Measure twice, then have someone else measure twice or you may be in for some unwanted fabrication aggravation!

    It would be a very good idea to do this calculation for ANY size adaptor you plan to use, a little math can save you major problems.
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    Not all of these standards come in all width bottom brackets. The fact that these three all have different diameters make it easy to determine what you have. The addition of the width will further confirm if you got it right. Look at the following chart for extra help.
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    The manufacturers of these adaptors is FSA (Full Speed Ahead) a well known established manufacturer of bicycle components. Other vendors offer these as "custom machined" parts. I'm guessing that means somebody with a lathe in their garage making them to order at a premium "custom manufactured" price. Buy from the established manufacturers if at all possible. The BB30 and PF30 can be ordered from QBP by almost any local bike shop.Variable PF41 adapter
    Variable PF41 adapter for Pressfit bottom brackets

    Luna locking PF41 adapter (discontinued)

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    Luna custom cut adapter for 41mm ID BB

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    From left to right:
    BB30 to BSA , PF30 to BSA, PF41* to BSA (*shown with bearing installed) Click image for larger version  Name:	bbadaptors.png Views:	1 Size:	172.9 KB ID:	10773
    More Resources:

    Here is a similar article on Endless Sphere discussing Bottom Bracket options and adapters
    Last edited by Sebz; 06-19-2017, 12:23 PM.

    To continue on the Carbon frames and the eccentric bottom bracket

    Here is a picture of a carbon frame as you can see it's really thick around the bottom bracket casing, probably more then 5mm max if it's a PF30 BB. Click image for larger version

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    Same thing goes for Eccentric Bottom bracket, if you don't know what it is, it's mainly used as a chain tensioner for single speed bikes and IGH hubs. But a eccentric as a thick side and a narrow side so it's possible to turn it to be able to install a BBSXX motor on it...depends on the eccentric locking system.

    Here is my other bike and as you can see I can manage to turn it till it's thin enough but the locking system is in the way, the only way is to cut the tabs off and weld it and then get an eccentric adaptor with an inner locking mechanism like the Cannonade system. Click image for larger version

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    But there are some exceptions like the Cannonade Hooligan (Eric's bike) : built thread

    The locking device is inside the adaptor so no protruding brackets like mine:
    Click image for larger version

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    Last edited by Sebz; 10-12-2016, 04:42 PM.


    • Mangeh
      Mangeh commented
      Editing a comment
      Hey. I have the exact problem with the eccentric bracket with the exterior lock bolts. I just wonder if you ever tried to fix it and if you succeeded? Sittning here with a new bike and motor, unable to proceed. Should have been more careful when selecting bike of course....

    I want to buy a Lynskey Endurance bike that has a : "MegaEvo BB386 68mm English Threaded Bottom Bracket" (as per their website). Everywhere I looked, this BB is 86mm in width witch further confuses me. It is also 46mm of outside diameter, same as the PF30. Could the PF30 adaptor be used to install my Bafang BBS02?


    • Sebz
      Sebz commented
      Editing a comment
      That's a though one.. the BB386 is larger but it's also possible that you have a standard 68mmBB threaded BB casing and it's just the crank set that is BB386..

      The only way is to remove the crank set and check... can be that you have this bottom bracket on it :