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BBSHD 73mm problem: rotating like a pendulum

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    BBSHD 73mm problem: rotating like a pendulum

    I have a 68 mm bottom bracket and ordered a 68mm BBSHD from Luna. But I received a 73mm unit. I asked for spacers, got them, but because they aren't serrated or stamped with little teeth like the mounting bracket is, it rotates in use even after tightening hard. I'm afraid to strip the threads of the BB by using a mega cheater bar. Spacers with extrusions or a second 5 mm mounting bracket (with its extrusions) used as a spacer would likely solve this problem.

    When I put in the spacers I banged them with a framing hammer first to rough them up, but it didn't do the trick.

    How have other people solved this problem? Are there still 68mm specific motors, or have they been discontinued with only 73mm's available?

    #2
    Gee,

    How about a photo or two?

    I mean, I haven't personally done a Bafang install, but I get what you're saying. And if you're filling space with more than one washer/spacer, it probably doesn't matter if the serrated one is gripping the BB, since the others slip between each other, i.e., a one-piece spacer from something like DOM tubing might be best, with added serrations as well.

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      #3
      Do you have the Bafang plate with the raised teeth installed directly against the bottom bracket? Spacers go outboard of that, not inboard, or it will rotate much more easily.

      You may need different bolt spacers to do that...
      Fabrication is fun! Build something today. Show someone. Let them help. Inspire and share. Spread the desire.

      Comment


        #4
        Originally posted by JPLabs View Post
        Do you have the Bafang plate with the raised teeth installed directly against the bottom bracket? Spacers go outboard of that, not inboard, or it will rotate much more easily.

        You may need different bolt spacers to do that...
        This ^.

        I have 20mm of spacers between my locknut and the bracket/BB - no movement so far.

        Comment


          #5
          Originally posted by Stu Summer View Post
          I have a 68 mm bottom bracket and ordered a 68mm BBSHD from Luna. But I received a 73mm unit. I asked for spacers, got them, but because they aren't serrated or stamped with little teeth like the mounting bracket is, it rotates in use even after tightening hard. I'm afraid to strip the threads of the BB by using a mega cheater bar. Spacers with extrusions or a second 5 mm mounting bracket (with its extrusions) used as a spacer would likely solve this problem.

          When I put in the spacers I banged them with a framing hammer first to rough them up, but it didn't do the trick.

          How have other people solved this problem? Are there still 68mm specific motors, or have they been discontinued with only 73mm's available?
          It is a problem - I wish Luna sent me the correct motor kit as well, since the required bushings added complexity and delay to my build (I didn't get them with the kit). I just started having the same rotational failure this past weekend too, so now I have to fix it. The correct kit would have eliminated the whole bushing/rotation issue and made for a MUCH more solid build. There is a 68mm-specific kit available from Bafang, but it seems Luna considers them identical to the 73mm kits, even though they are not. I have seen pictures of kits with a 68mm sticker on the bottom of them, and have read of Luna-supplied BSSHD builds that went right on to a 68mm bracket w/o shims, so I'd guess that Luna does (or at one time did) have them, although they say they don't exist.

          The only idea that I came up with, although I haven't executed it yet, is to drill a couple of teeny holes horizontally through the side of the bushing and into the side of the bottom bracket, then slide small steel pins into the holes - I figure I could make pins by cutting brads. The pins should stop any parasitic rotation, assuming the mounting plate teeth can dig in to the side of the non-drive side bushing. Perhaps some loctite or epoxy during assembly too. I hate that I'm going to have to completely disassemble the motor and wiring to muck with the bushings though. REALLY wish they sent me the 68mm kit in the first place.

          Also FYI - shimming the full 5mm on the non-drive side (keeping the drive side tight against the BB) centers the motor/cranks on your frame. I didn't have chain ring clearance for that using the Eclipse chain ring, so I used one 2.5mm bushing on each side. That results in a 5mm crank to frame offset, but I haven't noticed it.
          Last edited by JayC; 06-06-2016, 09:05 AM.

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            #6
            I too considered the drilling/pins idea.
            Then I bought a proper tool to tighten the inner lockring, and my motor has not moved since.
            I have last year's BBSHD, wich says 68mm on it.
            I just installed a new BBSHD, wich says 73mm on it, on friend's bike.
            Our bikes are both 68mm bottom brackets, and the units both installed the same.
            We both have Eclipse chainrings and both builds required a spacer on the motor, and the chainring for optimum frame clearance, and chain line.
            We are both having astounding good times riding cutting edge trail weapons!
            These kits are awesome! But getting one setup is not absolutely simple, but believe me, it's worth it.
            Lunacycle is trying like crazy to provide install videos, and these forums have a wealth of information about installs, but each install has complications you must overcome.

            Comment


              #7
              There is no difference between the 68 and 73mm drive....just the mounting hardware that comes with the 2 kits is a little different. We compared two drives ourselves and then got confirmation of this from bafang. The new drives we get from bafang will be stamped 68-73mm just to make this point clear. With our spacer kit it makes no difference if your drive says 68 or 73 on it.

              Comment


                #8
                It is NOT a problem and all customers were sent correct motors. Anyone who has followed the progression of the BBS series motors understands how it makes the most sense to have a single kit fit a range. Please, if you're having a problem it can be sorted. I have yet to have a drop. With the 68-73MM kits in 73MM or 68MM installations. I've never read a sport of anyone over torquing the lockring.
                I never had a drop using a simple Hozan Bicycle Bottom Bracket Tool, C-205 Lock Ring Wrench. Click image for larger version

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                I now use the Bafang tool because I like tools and wanted to add a bit more torque for the HD. I know use a 1/2 drive ratchet, or breaker bar. But my Hozan installed is still holding. As long as that fixing plate is properly installed and a bit of BLUE loctite, Bob's your uncle!

                Comment


                  #9
                  I think it would be possible to fix the motor in its position by having some sort of clamp, maybe a hose clamp, mounted to the motor housing, then a clamp with a rubber insert around the down tube, and then fixing the two clamps together. Maybe not the most elegant solution, but the motor would never be able to rotate, even if the locknut came loose. Or you could make a bracket and bolt it to the motor together with the original bracket, have it go a few inches up along the down tube and clamp it. Just a thought.

                  Comment


                  • Lance Tesla
                    Lance Tesla commented
                    Editing a comment
                    Or you could just tighten it properly using the correct tool.....

                  #10
                  Using spacers does NOT cause an inability to properly lock the motor. What you need is sufficient clamp load (from tightening the nut) to press that motor bracket against the bottom bracket, so hard that the bracket teeth dig in to the frame. The bracket's teeth need to be against the BB for that to work. Spacers neither prevent that contact, nor reduce the clamping force; they don't cause the problem. Only mis-assembly or insufficient clamp force will let the motor swing.

                  --

                  Stu,

                  Below tells me you either have yours together wrong, or perhaps you misunderstand how it's supposed to work.

                  Originally posted by Stu Summer View Post
                  I have a 68 mm bottom bracket and ordered a 68mm BBSHD from Luna. But I received a 73mm unit. I asked for spacers, got them, but because they aren't serrated or stamped with little teeth like the mounting bracket is, it rotates in use even after tightening hard.
                  Spacers shouldn't interrupt the function of the provided serrations, in any way, if placed outboard of the motor bracket as intended. I asked you about this above, but you didn't answer.

                  Originally posted by JPLabs View Post
                  Do you have the Bafang plate with the raised teeth installed directly against the bottom bracket? Spacers go outboard of that, not inboard, or it will rotate much more easily.

                  You may need different bolt spacers to do that...
                  It sure sounds like you have the spacer INBOARD of the motor bracket. Do you? If so, that's your problem. If not, need more torque.
                  Fabrication is fun! Build something today. Show someone. Let them help. Inspire and share. Spread the desire.

                  Comment


                    #11
                    Originally posted by JPLabs View Post
                    It sure sounds like you have the spacer INBOARD of the motor bracket. Do you? If so, that's your problem. If not, need more torque.
                    The spacers have to be placed under the motor bracket. The spacers act to increase the BB width from 68mm to 73mm, as the motor requires a 73mm BB to be mounted. Unfortunately, to properly center the motor on the frame, the entire 5mm must be shimmed out on the non-drive side, which puts the spacer under the motor bracket, eliminating the contact of the 'teeth' on the BB. Putting a spacer on the outside of the mounting plate wouldn't accomplish anything.

                    Comment


                      #12
                      It does not. "Properly centered" is centered so that the "fixing plate" (helps to use Bafang nomenclature to avoid confusion) is against the BB. These are kits. Kits designed to fit numerous frame designs. That means varied chainstays and BB positions as well. Properly installed the fixing plate is against the BB. Putting the spare on the outside of the fixing plate IS needed on some builds to take up the 5mm excess.

                      Comment


                        #13
                        Stu Summer
                        Junior Member



                        There has been some talking past each other.

                        There are two considerations for my particular mounting problem:

                        1. I need to put the spacer on the non-drive side in order to get an acceptable chain line.
                        2. With no spacer on the drive side, on the 73mm unit the studs that the fixing bolts thread into stick out further than the face of the BB. Therefore spacers have to go between the fixing plate and the BB shell.

                        Louis is right that " Properly installed the fixing plate is against the BB". I hope everyone can understand why "Putting the spacer on the outside of the fixing plate IS needed on some builds to take up the 5mm excess. (Louis)" doesn't work.

                        A simple fix, which I have not found yet, is a 5 mm serrated spacer that would mimic the serrations of the fixing plate.



                        Comment


                          #14
                          Use a second lock ring in place of a spacer in some cases.

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                            #15
                            A 68 BB with a measly 5mm of spacer should not be an issue at all. I have the 100mm BBSHD in a 68mm BB with 8mm spacers on the drive side, and 21mm spacers INBOARD of the mounting plate on the non drive side. I was concerned about this exact issue back during the build and even created and posted this video explaining the worry.

                            Original post here

                            As the replies stated just using enough tightening force has prevented this from rotating for over 1000 miles. My lock ring tool is pretty wimpy so I just used a standard pipe wrench taking care to not scrape the BB shell. This was not a monster wrench, or a breaker bar size wrench, just a regular 11" long pipe wrench.

                            An additional note is that Bafang uses the drive side bb shell face as its reference point so no matter how you space it the Q factor will be reasonable. In this case even though there are 21 mm of spacers on the non-drive side, the Q factor is only off center to the right ,by the 8mm I shimmed from their reference point, even with a BBSHD kit nearly 30mm extra long.
                            Last edited by Bicycle365; 06-14-2016, 06:29 AM.

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