Giant Twist Express 2 Hub Motor Repair

With these tests passed, it became necessary to strip the motor for inspection. Access to the motor is simple enough, removal of three bolts (Fig: 1) allows the motor to be withdrawn from the hub shell.

Removal of the freewheel shell and ring gear shell exposed badly worn planetary gears (Fig: 2). I then removed the gear carrier and noted that the planetary gears rocked on their spindles which presumably contributed to tooth wear. The teeth on the inside of the ring gear were similarly worn. The sun gear on the motor axle looked fine as did all bearings. The fix is to replace these worn gears.

Finally, after months of searching, having given up hope of finding parts, I asked the good folks on the UK Pedelecs forum for suggestions on a replacement motor. User shemozzle999 pointed me to these gears on aliexpress.com at a cost of €15!

The gears took about a month to arrive and, on inspection, appear to have a brass bush in the planetary gears which should make tooth wear less likely (Fig: 3).

First, remove the wheel from the bicycle (Fig: 4), two socket cap bolts through the motor torque plate, two electrical connectors (white three wire power and black six wire hall sensors) and the standard axle nuts.

Open the hub by undoing three socket cap bolts (Fig: 5) and the motor can be pulled from the hub shell. Note: the three inner socket cap bolts retain the freewheel ratchet ring to the hub shell. These do not need to be disturbed.

The motor assembly (Fig: 6) consists of: motor, planetary gears and carrier, ring gear and shell, freewheel ratchet and shell. The body of the motor and the planetary gear carrier remain stationary and make up the axle of the wheel while the planetary gears are driven by the motor and, in turn drive the ring gear and thence the freewheel shell. The freewheel shell is the outer right plate of the wheel hub.

Inspection of the planetary gears revealed severe wear of their teeth (Fig: 7). The original size of the teeth can be seen at left of the figure.

The planet carrier is removed by opening three socket cap bolts (Fig: 8) and gently prying off the motor body. Take care to recover thrust washer and two o-rings from each of the planetary gear shafts. The planetary gears can then be pulled off their shafts. It wasn't clear to me if the original planetary gears had brass bushings or was the plastic just bearing against the shafts but they were fairly worn such that the gears would rock on the shafts.

With everything nice and clean, reassembly is just the reverse of disassembly (Fig: 10).

The planetary gears themselves were subjected to a generous coat of grease before reassembling onto the shafts (Fig: 11).

The planetary carrier was then greased and fitted. Tighten the retaining bolts down evenly as the fit is quite tight (Fig: 12).

The ring gear was mounted to its shell, greased and slid onto the planetary carrier half-axle (Fig: 12). Note the missing bolts which were destroyed at removal. I had to hunt down new bolts for this.

The freewheel shell and its washers were slid onto the half-axle and bolted in place (Fig: 13).

Before refitting the motor into the wheel hub, I mounted it in the forks to test (Fig: 14).

With the motor repaired, I re-fitted the front wheel. This wheel has no torque arm, instead, the motor housing includes a U-shaped section which wraps around the fork end and bolts to a retaining plate on the other side of the fork (Fig: 15).