If you want just to replace the bearings you do not need to open up the electrical switch. If you need to open up the the electrical switch make sure all cables go free from the rotor when you put it together again. Also make sure the internal cables do not push to hard on the motors copper windings.
The rotor looks really nice
Here are some pictures from my UM 400 motor rebuild. Both the berings in the motor and in the planetary gear needed to be replaced. The bearings in the motor are two SKF 6203-Z and in the planetary gear two SKF 6005-Z. I will buy new bearings at Momentum tomorrow, and continue the assembly.
A previous owner have had the machine in a cold and humid environment. It shows even on the inside of the motor.
Type plate on the engine
The disassembling begins
A little rust on the rotor
Tight to get this bearing off
After a light blasting
Some light blows on the screw heads to loosen them a little
Planetary gear starts to come apart
Some rust to be removed
Cleaning the axle in the lathe