Bafang Motor Came Loose

[HillAversion]

I put my Bafang kit together in October. I took my time and was careful. The bike has been great.

The last couple times I rode the bike (on a very bumpy dirt trail) I noticed some chain noise in a couple gears. Yesterday I put the bike on the stand to do some derailleur adjustment. When I flicked the throttle I saw the whole motor bouncing around, along with the cranks and chainring. I couldn't believe how loose the whole thing had become. It was hanging straight down rather than being snugged up against the tube. You can't see it when you're on the bike. I had no idea.

I took off the crank and snugged everything back up, using Loctite on the lock nut. I torqued it down hard and banged the hell out of the wrench with a mallet. I'm going back out tomorrow to the bumpy trail so we'll see how it does. But in researching and thinking this through, a couple things occurred to me:

• The Bafang tool they give you for this job sucks. I torqued it as hard as I could and banged it with a mallet a few times when I first assembled it. That obviously wasn't enough. It's a little short, dinky wrench that doesn't bite too well and you really can't get much leverage on it.
• Lekkie makes a custom locknut (with more teeth) and Park Tool makes a socket for it. Together they cost about $50. I think I'll buy them and use a large torque wrench at the next overhaul.
• Meanwhile, I'll keep a close eye on this. I won't be surprised if this happens again. Anybody who's done a Bafang build should probably do a close check every couple months just to make sure everything's good and snug. I don't think this would have created a dangerous situation, but it could have meant a long walk home pushing the bike. And it could have conceivably damaged the motor, the bottom bracket or the chainring. Forewarned is forearmed.

 

[m@Robertson]

You are on the right track. The Lekkie OneNut is a recent entry, and it does work, but a much cheaper alternative is out there: Use two inner lock rings instead of an inner+outer. Their parkerized finish helps the two form a jam nut. Also use a 1/2" automotive torque wrench and torque the lock rings down to 90 ft lbs each. You'll need about a $35 lock ring socket though. Lekkie makes one, and so does Bafang although they can be a little tough to find.

Make a registration mark across the lock rings and your frame, and you can glance down every once in a while and know in an instant everything is fine.

If you are doing singletrack and drops, the next thing to do is the Hose Clamp Trick. Read about it here. This link is tee'd up to the section on final motor installation. Has description, pictures tips etc. etc.

How To Build An Ebike From Scratch: Assembly Day 1

The first day of assembly is laid out here item by item. By end of day we’ll have a roller we can sit on and push around, not a box of parts we have to carry.

talesontwowheels.com

Don't get involved with the aftermarket frameworks/braces you can Frankenstein onto your frame. Not necessary. The lock rings are plenty for street bikes and the hose clamp will hold firm unless you throw the bike out of an airplane without a parachute.

 

[HillAversion]

You are on the right track. The Lekkie OneNut is a recent entry, and it does work, but a much cheaper alternative is out there: Use two inner lock rings instead of an inner+outer. Their parkerized finish helps the two form a jam nut. Also use a 1/2" automotive torque wrench and torque the lock rings down to 90 ft lbs each. You'll need about a $35 lock ring socket though. Lekkie makes one, and so does Bafang although they can be a little tough to find.

Make a registration mark across the lock rings and your frame, and you can glance down every once in a while and know in an instant everything is fine.

View attachment 9163

If you are doing singletrack and drops, the next thing to do is the Hose Clamp Trick. Read about it here. This link is tee'd up to the section on final motor installation. Has description, pictures tips etc. etc.

How To Build An Ebike From Scratch: Assembly Day 1

The first day of assembly is laid out here item by item. By end of day we’ll have a roller we can sit on and push around, not a box of parts we have to carry.

talesontwowheels.com

Don't get involved with the aftermarket frameworks/braces you can Frankenstein onto your frame. Not necessary. The lock rings are plenty for street bikes and the hose clamp will hold firm unless you throw the bike out of an airplane without a parachute.

Good points; Thanks for chiming in.

I was actually thinking about using a hose clamp to secure the motor, but I couldn’t quite visualize a way to do it. The photo in that article is perfect. Very helpful.

I gather that the article refers to using two Bafang locknuts together. Sounds workable, but I hate the fact that those things only have three shallow points of contact. I’ll probably just spring for a sixteen point solution. I think Park Tool makes a socket for about $25. Small price to pay for long-term reliability. Anything worth doing is worth overdoing. Along with the hose clamps the whole thing aughta be bulletproof.

Thanks again for your helpful input.

 

[m@Robertson]

Four points of contact And if you can use a properly-matched socket to put 90 ft lbs of torque onto it, thats pretty robust. Luna Cycle's assembly spec was actually 100 ft lbs, but they only used one inner ring. I have bikes built in 2017 and 2018 that have never needed to be touched since original assembly. That is so much torque you need to put the bike on the ground to do the tightening. Can't have it in a workstand clamp.

If I didn't already have the sockets (I have a set Luna manufactured for a very limited time) I would be doing the OneNut. I believe the OneNut socket pattern is identical to a Shimano bottom bracket cup tool. But for my builds, a second stacked lockring is a permanent $4 solution.