Use a flat blade screwdriver to remove the casing off the Plasma Dash motor, see below.
Once the can is open, pull out the armature. Here's a picture comparing the Plasma Dash armature against the Kyosho stock Mini-Z motor armature. Notice the differences between the two. I could write paragraphs on the differences between these two armatures, thank your lucky stars I'm not...
The next thing we need to do is to remove the magnets from the ATOMIC can. They come shipped with a pair of neo magnets already installed, we want to remove those magnets. Use a flat blade screwdriver to lift up the two retaining springs holding the magnets in. Once the springs have been removed it's quite easy to pull out the magnets.
This is the crucial part. Now place the Plasma Dash armature into the ATOMIC can. Without any magnets in it. Once that's done, replace the end bell as well. See the pictures below:
Now, holding the end bell closed with your hands, try spinning the shaft. If everything is well, then the armature should rotate for several seconds showing no sign of being forcibly slowed down by any funny pressures within the ATOMIC can. If you find that the armature stops spinning a little too quickly then ream out the bearing hole again to help with the results.
Here's a video I've prepared showing how much the armature should spin freely within the motor can.
Plasma Tuning Video (WMV, 500KB)
It is very important that you get this part right. I have seen a few plasma/ATOMIC motors underperform because this step wasn't done.
Once you're satisfied with the free spinning rate, disassemble the motor since we're now going to put the magnets in it.