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Xiongda 2-speed motor repair: nylon sun gear

It seems clear the Xiongda 2-speed motor is a somewhat more fragile unit than the standard simple geared hub motor (e.g. the Bafang). Up to now we’ve had 2 XD 2-speed motors in our family, which my son Jasper and I depend on for day-to-day transport up and down the mountain. Each motor has done about 4000km, and both have needed repair. has a long and very informative discussion of the XD 2speed here:
I consider this weakness to be well worth living with, considering the excellent characteristics of the Xiongda 2-speed, for our mountain riding conditions. I also expect Xiongda will resolve this problem with improved materials (I am currently waiting on delivery of some new improved gears, Sept 2016).
It's also worth considering that nylon gears in any geared hub motor have a limited life in heavy climbing (see my post about replacing Bafang planet gears). My Bafang SWXB did 7000km of mountain riding before needing new gears, and our Xiongda 2-speeds have done over 4000km on one sun gear so far. Changing nylon gears is a cheap and easy service to do occasionally for the tremendous benefits we get from geared hub motors. 

Failure of the nylon sun gear

The most common problem seems to be failure of the nylon sun gear in the hub motor. This is what both of our motors have had. One failed in less than 1000km, due to a known quality control problem in that batch of nylon castings – there were clearly visible gas bubbles. The other went to nearly 4000km before breakage, and it’s unclear if this was a quality control problem.
The nylon sun gear transmits power in high gear - low gear power goes thru the nylon ring gear which surrounds the sun gear. For a video explanation of how the Xiongda gears work, see my youtube video here

How breakdown happens

When my front wheel motor failed, I was travelling slowly uphill and suddenly the wheel completely locked up. When I tried pushing the bike along, the main hub started unscrewing from the clutch plate (the right hand end of the motor, which screws in with a RH thread). This was troublesome but made opening the motor very easy. On opening up, we could see that the nylon sun gear had broken into large pieces which jammed other gears. This could have been dangerous at speed. 
My front motor with shattered nylon sun gear
When my son’s rear motor failed, the motor still freewheeled, and even ran roughly in low gear. This was because only the teeth had broken on the nylon sun gear, and only small pieces were free inside the hub. On opening, it became clear it wasn’t a good idea to run the motor after breakdown, as the small nylon gear pieces were jammed into other gears, particularly the nylon ring gear and its steel planets. Overall it was a much safer way to fail. 
Rear motor with broken teeth on sun gear

Service from Xiongda

Bonnie at Xiongda has provided excellent service in response to breakdowns, with parts arriving in under a week. 

Repairing the gears

The first step in repairing the motor is unscrewing the clutch unit. This threads into the RH side of the motor with a RH thread. 
On the front motor this was easy. The jamming motor unscrewed the clutch mostly, so I only had to spin it off by hand after removing nuts and washers. 
The rear motor was hard to unscrew. This is not surprising as the thread is tightened by both the motor torque and the pedalling torque through the cluster. We made a tool to bolt on, but the clutch unit was so tight I was worried we would break or strip the 2 M5 bolts. 
Home made tool to turn clutch unit
We poured boiling water on the main hub (tilting it to avoid any water on the bearings or wires) to expand it, and eventually moderate force cracked the clutch loose.
This youku video shows a charmingly easy unscrewing of the clutch unit, presumably by a Xiongda technician. 
The nylon sun gear is front and centre of the motor after removal of the clutch unit. Levering it up with a pair of screwdrivers easily lifts it out of place. 

Make sure to remove all pieces of broken gear from inside the motor. I used a scriber to scratch any pieces from between the teeth of the ring gear and the steel spur gears – there were a few pieces hiding in the sticky grease. 
Here is the nylon sun gear lifted out of its place
The replacement nylon sun gear easily slips into place. 
Take care about removing the steel gear plate (and opening the inner planetary gear set), as there are only certain positions that enable all gears to mesh. There are often pen marks on the steel planet gears which need to be all facing inwards – I have centre-punched these marks on some of my gears to be more durable. Here is a youku video of a Xiongda motor being opened and the gear plate being taken off (and an impressive display of concrete quality). 
Reassembly is straighforward, but here's a youku video to show how. 
There is much discussion on Endless-sphere about how best to lubricate these motors. I really don’t know. I haven’t been able to import any of the grease recommended by Xiongda, as it is not able to be transported by air. Some users use liquid lubricants on the clutch unit, which makes sense, but isn’t explicitly supported by Xiongda. I’ll do some experiments myself. 

Xiongda repair videos on Youku:

Opening the motor case:

Taking off the freewheel unit:

Replacing the nylon sun gear:

Main page:


  1. Hi Bruce - Do you have contact details for Xiongda?

    1. Email Bonnie Xiong at:
      Bonnie at