[KrazyCarl92]

Definitely follow the suggestions in the other thread if you can, but if you still experience difficulty or don't have arbor presses, mallets, etc., you could run the motor while lightly grasping the shaft with sand paper to slightly reduce the size of the shaft until the pinion can slide on. This definitely isn't the proper way to do things, but it will work as long as the retaining ring can fit firmly over the gear.