At ~2000 hours of printing I have noticed some of the belts have a fair amount of wear in certain spots. I believe these are the belt spots where the machine makes quick movements many times over the lifetime of the printer since our tendency is to print in the center/center location most often. I found instructions for reinstalling the X-Axis belt (extruder carriage belt) and the two Y-Axis belts, but I was unable to find a tutorial for how to re-install the small rear Y-Axis belt so I had to figure it out.

Upon completion of the belt changes, I believe the easiest way to access the rear Y-Axis belt was removing all 4 exterior panels and the rear right pillar. I was contemplating removing the whole upper frame piece + carriage off the pillars and lifting it out but decided against it since I have extra wiring ran along the ceiling which I would have to re-wire to remove the top. In my situation, the rear left limit switch and rear center limit switch had to be disconnected to allow the whole carriage to drop. Once all the panels are removed from the printer I removed all 16 top carriage bolts and it didn't drop on its own - it required a little bit of force to dislodge. After the carriage was dropped, I removed the two 8mm X-Axis rods from the X-Axis carriage sides and moved the assembly out of the way. This allowed me to move the rear X-Axis connecting rod within the rear right bearing housing so the pulley could be removed. I loosened all the set screws on both the belt pulleys in the rear right bearing housing and slightly tugged on the rear X-Axis connecting rod until it freed up the outermost pulley so it could be removed.

Finally, once the pulley was removed I re-installed the new belt, re-positioned and re-tightened the pulley set screws, and reassembled the X-Axis extruder carriage with rods. I took care to tighten the pulley set screws on the rod at nearly the same distance it was before for both the X-Axis rod distance and long Y-Axis belt position. I didn't have to do any tightening of the small rear Y-Axis belt and was able to get it onto the stepper motor pulley when reinstalling the rear right pillar. If you are replacing the X-Axis extruder carriage belt, this would be the time to get it wrapped in the right position if you are not comfortable lifting the extruder carriage off the 8mm X-Axis rods while the machine is together. The toughest part was getting the whole carriage assembly to stay together while I tried to lift it into place to get the 2 screws in needed to hold it up. The below image shows where the 2 screws should go to hold the carriage up temporarily while making sure everything else is ready to be fully assembled.

The rear pulley set screws for both sides were loosened and re-tightened after the final assembly - hopefully avoiding any future rubbing/vibration caused by improper balance/mounting/wobbling, remembering my battle with the creaking bearing I had prior ( The pulleys were also moved slightly away from each other (maybe 0.1 - 0.25mm?) in order to maintain separation from other parts that could cause issues. The belts I replaced were for the X-Axis carriage and rear Y-Axis that attaches to the stepper - I chose to not replace the two long Y-Axis belts as the wear on them was minimal compared to the two main belts and they look really easy to replace ( if I don't have issues with the gluing as noted before. The extruder fans were also replaced since both of them were whining loudly.

Hopefully the above information can assist someone else in replacing the rear Y-Axis belt/pulley which is probably one of the hardest things to change in this printer from what I've seen. The process should apply to the Flashforge Creator Pro along with other "clone" printers. Everything took me 5 hours including the rewiring of the extruder fans and the most lengthy part was probably me searching online to see if someone had done this prior and documented some of it. I was up and printing again by the end of the night allowing me to run an overnight job that turned out great! There was definitely a minor improvement in print quality by replacing the 2 main belts and I'm glad I was able to figure it out in one day.