bafang hub motor getting noisy

headwind

headwind

10 W
Joined
Mar 27, 2013
Messages
76
Location
Australia
Hi folks,
After almost a year of e-bike goodness, the BPM geared 36V500W hub motor is getting noisier. Under load, the whine is louder these days, especially above 30 km/h. I am running it at 44v and 30A.

The plan is to pull it apart to hopefully find the cause. What should I be looking for?

Thanks,
Simon
 
If water's got in, they go a bit rusty. Hopefully, it'll only need re-greasing. You can get new gears and clutch for not a lot of money if there's anything wrong with yours:

http://www.greenbikekit.com/bafang-bldc-hub-motor-clutches.html
 
So I ended up experimenting with ATF to reduce the noise... here are the results so far...

The motor noise is about normal for a year-old BPM, since Ben kindly let me ride his bike for comparison. Mine isn't hideously loud or anything, but I am convinced there is a bit more whine than when it was new, and I do like to be stealth! So, after reading a couple of posts about ATF making them run quieter, I removed the grease and added 50mL of ATF. Thanks to Marc S for his advice. About 100km later, I removed the awful gunk mix of ATF and disolved grease, and added 50 mL of fresh ATF.

Motor efficiency seemed to be reduced by ~25% initially (or maybe I just got lazier for a while??) but now it seems back to normal. And the noise? Yes, it is reduced, it seems to be back to the volume of the motor when new.

But I forgot just how evil ATF is :lol: It gets everywhere! It is weeping out of the motor cover and the back half of the bike has a thin sheen of it. Yuk. I might experiment with better ways of sealing the motor cover, but I suspect in the end I'll go back to grease. With a new clutch and gears (that d8veh linked above- thanks!) to make it quiet. Since ATF disolves grease, the issue will be getting the motor thoroughly cleaned of ATF before putting it back in with grease.
 
A spray can of Brake Cleaner from your local auto store would get rid of the ATF and any other residue. But it's a pretty powerful solvent, so make sure you're careful where it goes.
 
After a years use you probably need to chage the two outer axel/case bearings as most of the originals were only shielded and not sealed.
 
Thanks for the replies.

Grinhill said:
A spray can of Brake Cleaner from your local auto store would get rid of the ATF and any other residue. But it's a pretty powerful solvent, so make sure you're careful where it goes.
Click to expand...
Ah yes, I should have thought of this. Aside from carefully wiping it down, are there any other ways to ensure there's no brake cleaner left behind to dissolve the grease?

jateureka said:
After a years use you probably need to chage the two outer axel/case bearings as most of the originals were only shielded and not sealed.
Click to expand...
My thought was that it was gearing noise, since it quietened when I changed the lubrication. Or would the change to ATF also affect these bearings? Any suggestion on where to get replacement bearings?
 
The bearings are all standard. You can get them from any bearing supplier.

6805RS (x2), 6904RS and 6810RS
 
headwind said:
Ah yes, I should have thought of this. Aside from carefully wiping it down, are there any other ways to ensure there's no brake cleaner left behind to dissolve the grease?
Click to expand...

The marvellous thing about brake cleaner is that it evaporates really quickly with NO residue! :D
Let gravity do the work so it flows downwards carrying gunk with it, i.e. you may have to hold it mid air with open end facing downwards.
 
The new clutch and gear assembly has just arrived, so I'm about to swap in the new one and revert to grease. Very much looking forward to the rear of my bike being no longer covered in a thin sheen of oil.

Any tips on how thick to lay it on and how to get the best coverage please?
I bought a tube of Castrol Premium Multipurpose Grease (replacement for Castrol LMX), hopefully this is ok?
 
headwind said:
But I forgot just how evil ATF is :lol: It gets everywhere! It is weeping out of the motor cover and the back half of the bike has a thin sheen of it. Yuk. I might experiment with better ways of sealing the motor cover, but I suspect in the end I'll go back to grease. With a new clutch and gears (that d8veh linked above- thanks!) to make it quiet. Since ATF disolves grease, the issue will be getting the motor thoroughly cleaned of ATF before putting it back in with grease.
Click to expand...

Can you describe, in detail, how you sealed your hub? Things like which sealant you used, how much and where are of interest.
 
No sealant. Anywhere.

Yeah, if I went to a bit of effort, maybe I could get it sealed. But I really hate dealing with ATF and the replacement gears are cheap enough, so I'm abandoning the whole ATF experiement!
 
headwind said:
No sealant. Anywhere.

Yeah, if I went to a bit of effort, maybe I could get it sealed. But I really hate dealing with ATF and the replacement gears are cheap enough, so I'm abandoning the whole ATF experiement!
Click to expand...

Would I look silly for pouring someone a cup of water using a cup that had cracks and holes in it?

Are you going to replace the bearings?

The gears inside the hub aren't made to perfection, the surfaces that contact each other have imperfections that are worn away as you ride so the surfaces become smoother to one another, reducing noise output. Eventually, the gears may wear away to the point where there is a lot of play or something to that degree(which might make more noise), so perhaps it's possible that happened, but I imagine it would take longer than a year to do this. Maybe you ride at really high wattage levels a lot or you've ridden an incredible amount of distance in a year. If not, new gears will probably be louder than old ones for a while, and certainly louder than ones lubricated with automatic transmission fluid.

Also, geared hub motors don't like to have their throttle go from zero to very high extremely quickly, this can damage gears. A cycleanalyst version 3 can be setup to automatically 'tame' a throttle for you, turning a rapid throttle twist into a somewhat more gradual one.
 
headwind said:
Cool.

Does anyone have tips for re-greasing the gears please?
Click to expand...

What tips do you need. You just take the side off and slap some grease on; however, if yours has become noisy, the cause could be something else, which might become more obvious when you open it. If yours isn't noisy, leave it alone, they're supposed to be able to go for 30,000 miles without maintenance.
 
If your hall connections are getting a bit touchy and your controller is a sensored/sensorless KU123 or similar, it'll start to make some resonant whines at certain frequencies. Might be worth checking the 6pin hall plug just in case. I went on a mechanical goosechase 12 months ago for a BPM, and it wasn't mechanical at all in the end...
 
Thanks for the replies.

Sorry if the questions about re-greasing the motor seems like I'm being overly precious! It's because every time I pull the motor apart, the wheel somehow ends up needing to go to the shop to get trued. So I'm keen to do it right the first time. I'm wondering how thick to apply it, and if there's any tricks to get it into all the places that need it.
 
They're polymer gears, so don't really need any grease. I think they only put it on to aid running in.. They're good for 30,000 miles, so don't panic.

Taking the wheel out or the side-plate off should have absolutely no effect on the spokes or the trueness of the wheel.
 
d8veh said:
Taking the wheel out or the side-plate off should have absolutely no effect on the spokes or the trueness of the wheel.
Click to expand...
In the past, my ham-fisted struggling has put the wheel out of true each time. But this time the wheel stayed straight. :D

More good news, the new clutch and gears (back to grease) have reduced the noise a bit. Maybe a touch louder under load, with a pulsing sound, a bit like dragging brakes. More likely, though, is that it's as quiet as when it was brand new and now I'm just being too pedantic about it!
 
did you replace the outer axle/case bearings too?
 
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