Hub motor cracking noise

[thanar]

Hello community,

It’s been a while now that my front Chinese hub motor has been doing cracking noises when riding. Only when riding. There is no bearing gaps whatsoever.

I found a similar case on YouTube: https://youtu.be/Z1tkmlh7fsQ

Any ideas? It’s getting worse. I thought it was the spokes, but I have now tightened all of them and the sounds is the same.

 

[amberwolf]

That video has a kind of thunking noise, but I don't hear any cracking.

In your case, does it happen once per wheel rotation?

Or is it less often? Or more often? Exactly how many thunks during each wheel revolution?

Since it only happens when riding, and not offground, it implies a problem with the wheel itself, where the weight load on it is causing a problem.

SUch a problem can be that the rim is bending enough to allow tire to touch the frame, and the rim could be untrue enough to let your tire touch the frame and make the noise (or the rim touch a brake pad).

Or if yours is disc brakes, perhaps the axle nut is loose on the disc side (or the axle is broken), so when sitting on the bike it pushes the axle up till the disc can touch the rotor at some point during it's rotation.

 

[thanar]

Thanx for chiming in. Brakes, rim, spokes, tire have all been checked. The noise is coming from inside the hub and is being amplified by the spokes. The period of the noise is on each tire rotation. Will try to upload a video of the issue.

 

[fechter]

I had one that did something like that. It turned out the spoke tension was uneven, causing the hub to get out of round and allowed the magnets to rub in one spot. You might also have a piece of debris stuck to a magnet. If you take apart the motor, you can usually see marks where anything is rubbing.

 

[thanar]

Here’s the video I promised:
https://youtu.be/WuREP1pscVc
It really sounds like it’s the spokes, I still haven’t removed the tire to examine spokes nuts.

 

[Chalo]

That doesn't sound like spokes to me. Are they very loose?

 

[thanar]

Everything is tight and checked by a professional. Then only think we didn’t do is remove the tire and check the spokes nuts to see if there’s any issues on the rim’s double wall. Oh, and crack the hub motor open, of course.

 

[d8veh]

It's clacking at wheel speed, so that eliminates just about everything inside the motor, since everything in there spins at 5 times the speed of the wheel.

One thing it could be is the wheel sensor magnet if it has one. They often detach.

It doesn't do it with the wheel off the ground, so it must be the spokes.

 

[amberwolf]

It is not in sync with the wheel rotation (actually appears to be sometimes faster than the wheel rotation), but it is not nearly fast enough to be synced with the motor rotation either. (you can see the stickers on the motor in different places when the sound occurs, and sometimes they are not visible at all when it happens).

It almost sounds like something is rolling around inside the motor casing...but if it was, it'd probably have gotten caught in a gear tooth or something else by now.


It does not have the right sound for a nipple loose inside the rim (dropped inside while building the wheel) but being different than the wheel rotation and not always the same period between sounds lends itself to that idea.

However...it would do it offground or onground if that were the problem, and the same is true of loose debris inside the motor.


A broken axle could allow for something different to happen onground vs offground, as could loose axle nuts.

 

[thanar]

Broken axle... hm, I didn’t think of that... that could also possibly explain why the sound is further amplified when I ride off center to the left, with the bike leaning to the right, and it almost completely eliminates if u ride the other way?

Spokes or axle it is then. Will investigate further and let you know. Thanx for the input.

 

[amberwolf]

OH, also, a bad axle bearing could do it, too, but it *should* make noise regardless, not just under load, even if it's a lot quieter without a load.

 

[thanar]

So I took apart the motor. Axle and gears all solid, no sign of wear. Applied some extra lithium grease. Removed a very small piece of loose wire that was included as a bonus from the Chinese manufacturer, however I don’t think this was the culprit (visible in attached photos). Close the motor and the noise is gone.
I believe it was coming from the motor cap, as seen in the pictures the screws have rusted a bit and it could be that a couple of them had become loose and the cover (which also holds the weight) was moving up and down a bit.

The forum really needs a tool to automatically downsize images. The 512k limit is obscure and very difficult to manage achieve through a smartphone.

 

[thanar]

Also did a nice slo-mo video of the hub motor in action:
https://youtu.be/nxUOtitpIe0

 

[amberwolf]

That bit of wire coudl actually be the culprit, floating between the case and the rotor bell. Probably not, but could be.

The cover should have a lip that sticks into the case, so it wouldn't move around circumferentially even if the screws were a bit loose (which tehy probably wouldn't be from rust--that usually makes them tighter.

 

[thanar]

The cover sure had a lip and it was tight enough that I had to apply quite some force to open it, but I don’t know, it’s fixed now. Will let you know if the noise finds its way back.

 

[dogman dan]

It was that wire.

 

[thanar]

:x :x :x
Noise came back just a 5km ride later, slowly ramping up the volume to previous levels.
What do I try next? Spokes rubbing together has been ruled out by placing thick electrical tape where they touch, noise still the same. Maybe spokes bases? Noise comes from the center of the wheel.

 

[amberwolf]

Since the noise is not synced with either wheel or motor rotation, it is almost certainly not something fixed to either one, but something else that rolls at a rate different than either one. So not spokes or rim or gears or motor internals.

The only other thing I can think of that makes sense with the unsynced noise is a bit of debris in a bearing, probably a chip off of one of the balls, or rust inside the bearing itself that caused wear on a bearing ball, so it's pitted. So as the bearings roll around, inside the races, the pits and/or debris change position at a different rate than the motor itself.

It is possible that the noise could be different under load than offground, because the pressure of weight on the bearings could make the "skipping" over the pit or debris harder and louder.

You may be able to test this by taking the cover off again, and putting your finger in the bearing's center hole, and spinning the cover. If it feels smooth, then try rolling the edge of the cover on a table/etc while pressing down on the center hole with your fingertip inside it. If you feel any kind of clicking or grinding, the bearing should probably be replaced.

The other side's bearing can be tested if the cover's bearing rolls smoothly, but you have to take the motor core out.

 

[thanar]

The noise IS fixed to wheel rotation, it just changes in volume and type, depending on the wheel slant and weight applied.
I did try the cap bearing when I opened the motor, but not thouroughly enough, didn’t test it under force.
I will be replacing ball bearings soon; I suspect they are using bearings out of fidget spinners or something!

 

[amberwolf]

The noise IS fixed to wheel rotation, it just changes in volume and type, depending on the wheel slant and weight applied.

THen the video and audio must be out of sync on the linked vid of the problem
https://www.youtube.com/watch?v=WuREP1pscVc&feature=youtu.be
because I can see the label at different positions (or not even visible) during various instances of the sound.

 

[dogman dan]

Hmm, loose magnet? they stay in place magnetically, but can click when they come unglued. Other one, not in this case because you should have noticed it on the teardown, cracked case at the freewheel.

 

[thanar]

My slo-mo video on the working motor covers all freewheel case, magnets and nylon gears, I believe. I see no issues whatsoever with the motor itself: https://youtu.be/nxUOtitpIe0

 

[dogman dan]

Chances are, if its a loose magnet, its sticking fine by magnet only on a no load run. Under load, it might start moving around and clicking, because it wants to move, but the load is not letting it really turn. so the magnet shifts, and clicks.

Hard to see which one is not stuck with epoxy anymore, unless it shifts out and sticks out from the line.


Sure its not your freewheel? Ive had plenty of them that click every rotation. That's when pedaling only though.

 

[thanar]

Are you referring to the freewheel of the back wheel, or the freewheel inside the motor (I suspect the is one build into there)? The motor wheel is the front motor, so it’s not from the back wheel’s freewheel.

 

[E-HP]

sounds like bearings