Tool for tightening Bufang bottom bracket ring

[Hakai43]

This ring tends to keep loosening so I need to get a tool to keep up with it myself. Several bike shops have tightened it, perhaps with the wrong tool to the detriment of the ring. Is there a semi-circular tool so that it can be tightened without removing the crank arm?

[Hakai43]

I’ve just learned that the ring shown is just a cap - underneath is a nut which does the work. Both require their own expensive wrenches, requiring removal of the crank arm. A job for the bike shop that has the right wrenches, and many don’t since they are specialty tools for mid-drives.

[RamboPat]

https://lunacycle.com/parts/bafang-p...allation-tool/

Luna sells this tool. Each side is for the different rings.

[RamboPat]

https://lunacycle.com/crankarm-removal-tool/

A tool to remove the crank as well.

[JPLabs]

https://lunacycle.com/parts/bafang-p...allation-tool/

Luna sells this tool. Each side is for the different rings.

I cut a slot in one of those, hoping to make it open ended to work without pulling the cranks.

Don't try that! It's beautifully light, but not strong enough to work open end. so you do need a crank pulled to use it.

For emergency tightening on trail, a hammer and punch type method works.

If you get it tight (and don't have motor set up to loosen it, meaning you need to rotate the motor against a hard stop so it can't lift up under torque) then it should not loosen. You should work towards that goal, really.

In my opinion, that Luna tool is not strong enough to really get the inner lock nut tight enough unless you are very careful - it tends to bend if you stand on it, for instance. I use a steel socket made for the job. It's not loosening up on my bikes.

[Hakai43]

Yes the guy at my local bike shop uses the socket on the inner nut and really torqued it. He’d done it before my 250 mile ride, and now it was loose again. It bothers me that it keeps loosening. Wondering if some green (removable) thread-locker would help.

[Hakai43]

I just digested your comment about needing to prevent the motor rotating under torque, and wondering if failing to do that is the problem. What is the “hard stop” procedure or set-up that you mentioned?

[JPLabs]

the motor wants to lift up in front, towards the frame, under power. You can just rotate against the frame before you tighten it, if that's possible. But, you should not stop it against a cable, or anything soft. Or in mid-air, without a hard stop.

Is that already your situation, or are you trying to keep the motor in place with the nut torque? If not against the frame, either rotate it up all the way, or make a spacer. I've used epoxy putty, wood blocks and glue, anything solid to resist that torque reaction, so the lock nut doesn't have to.

Also make sure the bumpy side of your steel motor bracket is against the frame. Those teeth help with the above, too.