DYS 1104 motors use winding wire in the heatshrink, which is somewhat brittle and has to be handled with care to avoid unwanted damage during installation.
To avoid issues: NEVER APPLY FORCE, NEVER PULL WIRES, HANDLE WITH CARE.
How to shorten motor wire?
Because of the nature of DYS motor wires the best way to shorten it is to just cut it with scissors or clippers and then to apply heat with the soldering iron to the peak of heatshrink and slightly pull heated heatshrink with your fingers.
Exercise caution in order not to burn yourself.
Heat shrink will become stretched.
Then you can cut it with scissors.
After that apply heat to the peak of heatshrink again, which will shrink it and expose wire.
How to prepare motor wires?
DYS 1104 motor wires are covered with enamel, which has to be removed before it can be soldered to ESC.
In order to remove it, just use hot soldering and move it up and down along exposed wire until enamel will come off, it will be easy to notice as you will see burned enamel on your soldering iron.
After that clean your soldering iron and tint motor wires in the preparation for soldering to ESC.