Tools and techniques for changing the Torque Sensor
Sorry, for some reason I didn't take any photos while doing this torque sensor replacement apart from the pictures of the torque sensors themselves.. see my previous post.
The torque sensor assembly is in two parts: the rotating assembly and the stationary coil.
If you only need to replace the rotating assembly, you do not need to take the cover off the controller, but if replacing the stationary coil as well, you will need to remove the controller cover so you can separate the connector from the coil to the controller.
Remove both pedal cranks, remove the cover over the large gear, remove the circlip that retains the big gear, then pull the big gear off. (For details of how to do these steps, find the very helpful video by forum member JBALAT) https://www.youtube.com/watch?v=u-SY0rGMEMo
Once the big gear is off, remove and put aside any shim washer between the gear and the rotating coil of the sensor, then move to the left-hand side of the motor.
Remove the oil seal from the pedal spindle by sliding a bent O-ring pick or similar between the spindle and the inner lip of the seal and hooking it out. in my case the seal came out easily and without damage.
A long-nose, straight pair of external circlip pliers with small tips is needed to remove the circlip on the pedal spindle as it is buried fairly deeply in the housing behind the seal.
Remove the shim washers behind the circlip and keep for later. This is tricky , but if you turn the motor on its side they might drop out.
Now turn the motor on its side so the pedal spindle is vertical with the left-hand side down, and tap upwards on the end of the spindle to drive the torque sensor out upwards. This is because the stationary coil sits between the rotating coil and the housing, and is pushed outwards into contact with the rotating coil by three small springs. If you tap out the torque sensor with the motor horizontal, the stationary coil falls outward, the springs jump out and hide behind any available object and are devilishly hard to find.. (don't ask how I know that..). If the motor is on its side, the stationary coil is held down by gravity and the springs will remain in place until you remove them.
If you want to replace the stationary coil, separate the connector at the controller and carefully lift the coil out. Retain the springs in place with a little dab of tacky grease and lower the new coil into place, aligning the recesses with the springs. The wires are stiff enough that threading them back through the opening in the housing is fairly easy. Rejoin the connector halves at the controller.
If you want to replace the bearing(s) at the left of the pedal spindle, tap them out with a drift from the right-hand side.
Reassembly is simply the reverse of the disassembly. Use anti-seize or grease an anything you want to come apart easily next time, and clean the motor gear and big gear and replace the grease with a good quality grease (Mobil 28 and Lucas Red ' n ' tacky have been recommended on this forum).
The bearing(s) at the left-hand side of the spindle are 28mm OD, 15 ID 7 wide, type 6902RS, and the oil seal is the same size as the bearings.
Sorry for the long post, but hopefully it will help somebody one day (even if only to keep possession of those little springs!