If you are assembling the AM CIM-sim, use care when installing the screws to mount the motors. We found you need to do one of three options relative to the screws provided to keep them from getting too far into the motors -
We were mounting FP and AM motors.
How much shorter do the screws need to be?
Thanks for the heads up 
We noticed the same thing, and we also noticed that our RS-550 motors had smaller shafts that allowed the pinions for CIM-Sim to fall off.
No complaints, though. It’s a pretty sweet little box.
Our finished size was .25".
Yes we found the same thing, but only after we had run our gearbox with too long of screws and it was binding completely. We may just not face mount ours.
We discovered that the threaded holes in the FP motors use screws that also fit CD drives, in computers…so look in the drawer in your computer shop that has those little screws. They’re usually shorter than you’ll find at the hardware store.
THe screws for the hard disk drives won’t work, they’re bigger.
Been there, done that, saw the sparks, replaced the screws 
Here is an additional heads up. When mounting motors to the CIM-Sim, note whether you are covering the air intake holes on the motor. If you are, drill vent holes in the CIM-Sim to allow cool air into the motor.