To build the 8108 class gearbox with the geartrain inside, first I need to get the motor apart and separate out the individual pieces that I needed. Here’s the first in a few posts about the modifications.
The original unmodified 8108 motor looks like:
To begin with, I needed to separate the rotor from the stator. First, there is a small screwed on plate which needs to be removed — it just has normal Phillips head screws.
After that, the rotor is pressed onto bearings. The magnets exert quite a lot of force on the stator, which makes removing them challenging by hand. I wasn’t able pull it off with all the force available just from my arms. For my first experiment, I built a simple fixture from two plates of aluminum and some bolts.
I bolted each half of the motor to one plate, and gradually tightened the bolts. This eventually liberated the rotor from the stator. Clearly something more robust and repeatable would be necessary to do this more than a couple of times, but this worked for a first iteration.
A Modicum of Fun 
Old post, but how did you get the bearings out of the stator holder? They’re pressed in pretty solidly in a few of the motors I’m disassembling, and I’m trying to avoid sourcing a small ID bearing puller if it’s not necessary.
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I never bothered to extract the bearings. When I extracted the stator, I just machined away the tabs connecting the center to the stator and then discarded the middle section, bearings and all. Well, I machined all but one tab, then used pliers to bend the final one till it broke. Sometimes the bearings came out on their own, sometimes not, but I didn’t want them so just got rid of them.
See https://photos.app.goo.gl/xPadnhaFtASVRSsz8
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