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BionX 250HT hub motor bearing replacement / disassembly, reassembly

The bearings in my BionX hub motor began to die at around 6500km, and now completely worn out at around 9500km. The wheel had a lot of play, and power consumption went up by about 30-40%. Surprisingly, I couldn’t find a lot of info on the web.

As always, this is not a complete guide, but I try to point out those parts of the procedure that were not straight forward to me. If you’ve done it yourself and have something to contribute, please do so using the comments function.

Tools / Parts needed:

  • Bearings:  SS 6003 2RS   Stainless Steel 17 x 35 x 10 mm
  • Strain Gauge: Mine survived
  • M8 bolts + nuts or similar, as tool (see below)
  • Freewheel removal tool
  • Spoke key
  • Hydraulic press
  • Bearing puller
  • Straight puller

I didn’t do it in the same order as I recommend here, but I think this is the best order to do it.

First step – Take the hub apart:

Remove the Freewheel

Remove the torque blocker (pressed onto the axle, brake side). Mine was just cone-shaped, but the newer ones seem to have a notch, so don’t try to rotate it, use a straight puller to remove it.



Remove the spokes on the brake side, this should suffice / I’ve left the drive side spokes in place. Mark the hub, so that you know how to align the halves when reassembling. I’ve used 9 M8 bolts and nuts to actually press on the inner walls of the hub shells. It was surprisingly easy to get it apart by doing so.


Second Step – Remove the bearings:

The bearing on the brake side covers the strain gauge, which measures torque applied through the pedals. I have read, that this will usually break during disassemble – luckily mine didnt. The bearing came off the axle / stayed in the hub shell. Getting it out of the shell was a job for a hammer + some alloy tubing.

To remove the drive side from the inner part of the motor, we have used a hydraulic press (sorry I somehow missed to take pictures). So this wasn’t easy, and I needed help from someone with the right tools. It eventually came out, and the bearing stayed on the axle.

Removing that bearing is quite difficult, as you don’t have much room below it, to actually use a puller tool. Luckily the mechanic had something like this (with barely enough room to house the cables while pulling):



Third Step – Reassembly:


With that bearing out of the way, it was time to clean the axles, place the new bearings onto the shaft. Add new silicone to protect the strain gauge, as well as replacing any heat shrink that has been removed. I then continued with adding the brake / magnetic side, but I’m not sure if it wouldn’t be easier to first push the axle onto the brake side, as there’s no magnetic involved.

Anyway, since I was back at my workshop, I didn’t have the hydraulic press available, and I’ve used my bench vice to gently press the hub halves together (lots of rotating / small steps were involved).

Add spokes, true the wheel go for a ride.


It’s running smooth again, so it was worth it. It took me about 5 hours to do it, If I’ve had the right tools from the beginning, it would have been much less. So if you want to do this, be sure that you have access to the right tools.

7 replies on “BionX 250HT hub motor bearing replacement / disassembly, reassembly”

First of all, thanks for the nice guide on disassembly procedure.

Can you explain in more detail how is strain gauge attached and to what? I absolutely, positively want to keep in one piece, as I have no way of getting replacement, and whole system is useless without it. If you have picture of it, it would be nice.

Suprisingly, there is very little info about that particular aspect of disassembly, and I would really like to NOT screw it up.

Thanks in advance 🙂

Hey Boba
Yes, it is surprising. Sorry the “Guide” didn’t get as detailed as I wanted, as not everything worked out as I wanted to, and then I went to my Car mechanic, who went to a motorcycle machanic with me…)
Anyway, the Strain Gauge is glued onto the Axle, and covered with silicone. Drive side, if you remove the Freewheel, you can actually see it (or part of the silicone). I actually don’t know why people seem to destroy it during disassembly, I have opened another motor (which luckily was a lot easier, was able with my own tools), and I didn’t brake it.

Hope it helped, good luck with your repair (whats wrong?)


Can you give me more details about removing the drive side lid from the axle. I tried to extract the axle with a hammer and it went out a bit bt does not want more. It also started wobbleing but I suppose I’ve already broken the strain gauge. Where I can buy a new one from ?

You shouldn’t use a hammer, it will damage the threads, and could even bend the (hollow!) axle. Try to find a puller or a press to do it. On one of my motors, I was able to do it with a simple puller, cheap one bought at a hardware store. But you could also ask a car mechanic, they should have one.
Strain Gauge is difficult to find, I’ve found the exact same, but only available in large quantities, I then bought some chinese with the same values on ebay, but I didn’t use them.

Hi Nico, I read in endless-sphere that some time after you replaced your bearings you had issues with stuttering and incorrect readings of the speedometer. Did you manage to deal with the problems, and how? I opened my motor, as it had fallen capacitors on the back side of the PCB and was shutting down when highly loaded. However during the rest of the time it was running very smoothly. I had errors 40 and 55, which I troubleshot for an year until I found what was the real reason, but I re-soldered the capacitors and after re-assembling everything very carefully, very same stuttering and bad readings of the speedometer appeared. However, the old issue seems to have disappeared- no errors in the status menu. I am wondering if it could be the strain gauge, or rather the hall sensors. If it is the former, I am not sure I can deal with replacing it, as I don’t know where to obtain a replacement from 🙁 I will be very happy if you can help

Actually, it seems that I’ve missed your last post in the forum – where you explained that you’ve replaced the BMS FETS and fried the motor 🙁 Sorry to hear that. I am pretty convinced that the issue should be in the motor, as after re-assembling it, the problem started. It should be either the strain gauge, presumably broken during disassembly, or a hall sensor re-glued either too far from, or too close, touching the magnets.

Hi Kosio – I didn’t replace my strain gauge, I actually don’t know why it should even brake while disassembling – it clearly survived. I’ve opened another motor, and the strain gauge survived as well.
I’m sorry I don’t have more information on this, as I gave up, it’s such a proprietary product, I didn’t want to invest too much effort into. I do have a working unit, and a modified Rack battery (in the frame box), but it’s currently not in use. Maybe I will use it in the future.
The broken motors that I have will be modified to external controllers. I’m also thinking about using the strain gauge with either a CA or the Arduino based Forumscontroller. My hobby time is very limited, so these projects will have to wait.
Good luck with your repair.

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