If that spring breaks, the gun won’t work, so take a look at that, make sure it looks good. For a video explanation of how the Xiongda gears work, see my youtube video here. The cell is sandwiched between a circular copper contact (attached to the single flexible wire you see running under the meter mechanism) and a large sprung metal contact. Pop it open and remove the rod from the inside door handle mechanism. Slide back the external door handle and then pull it out at an angle (rear first). Take those and set them aside carefully – you’ll need to put them back in before reattaching the handle. Once this is off the little door on the back for high/low range comes off. This shows that chipping of the glass is most often comes from the way the machine is used rather than the grinder head needing replacement. 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.
The other went to nearly 4000km before breakage, attributed to not having the optimal material. This was a new model (2017) sun gear, with stronger nylon material. The nylon sun gear transmits power in high gear – low gear power goes thru the nylon ring gear which surrounds the sun gear. When my son’s rear motor failed, the motor still freewheeled, and even ran roughly in low gear. More recently, I had a new motor (less than 1000 km) fail by a breakage in the sun gear unit. If your Xiongda motor has failed only because of the nylon sun gear, repair is quite easy. 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). I have written 2 posts about repairing Xiongda 2-speeds: this post, and another post about slipping magnets. A great post .
Dale Dougherty wrote a great piece in the current Make considering what makes a product Maker friendly. I consider this weakness to be well worth living with, considering the excellent characteristics of the Xiongda 2-speed, for our mountain riding conditions, and their low cost. Also some noise seemed to be the kind due to low oil lubricating noise. This resulted in a motor that could power in low gear, but in high gear the motor could be heard running but it couldn’t push the bike along (although the wheel would spin if lifted off the ground). From here, you just wiggle it a little, and push down. Push the thing, slide the carrier forward by grasping it up on the magazine tube. Oddly, the driver side axle literally fell out of the axle tube and I merely removed it by hand. Remove the small exhaust tube with the sensor on the top and set it aside. Put a thin film of lubrication or penetrating oil on the shaft and then you can hold the top of the shaft tight with smooth-jawed pliers while you twist the bit.
With the steel boss in the vice, I can twist the nylon gear with steel liner around on the boss. That’s because the little TIG welds have broken, and that’s why the motor can’t drive in high gear with this broken sun gear. 3/4 drive socket wrench, with an extender bar. A sprung bar presses on the needle to prevent it moving until you press the button on the side. If the motor slows as you press the glass to the bit, you are applying too much pressure. 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. I repaired this unit by simply replacing the sun gear. All breakdowns have been repaired in our workshop, without cost, although I expect over the long term we will need to keep replacing nylon sun gears at our own cost (a very cheap repair). I also expect Xiongda will resolve their problems with improved materials. We have 4 Xiongda 2-speed motors in our family, amongst the bikes we depend on for day-to-day transport up and down the mountain.
The old Sangamo Weston Master light meters seem to have a bit of a cult following with the most desirable being the Weston Master V and the Euro-Master (which is still being made!). To complete the circuit from the sprung metal contact on the cell to the meter mechanism relies on 2 bolts being on tight. Remove 3 bolts attaching it to the frame. I forgot to take any pictures at this point but you simply remove the meter mechanism then keep unscrewing the odd nut/bolt pieces (remembering the order in which everything came out) until you get to the cell. A stiff wire that runs from near the upper range limiter on the meter to near the scale mechanism completes the circuit. Putting it back together is pretty easy apart from locating the ends of the springs from the door on the back into the holes in the moving part of the scale mechanism. Next unscrew the knurled part in the middle of the dial on the front.