A carriage upgrade kit for the X5S.
I was annoyed by the four-wheeled design of the original carriage, since its fourth wheel and 40.5mm hole distance made tightening it properly a nightmare.
Since I'm using printed sleeves on 608 bearings (https://www.thingiverse.com/thing:3188237), the belts were also not straight towards the print head, front idlers, and motors.
This kit intends to fix all that.

Parts you need:
1x "y_carriage_right.stl"
1x "y_carriage_left.stl"
1x "frontidler_r.stl"
1x "frontidler_l.stl"
2x "pulley_smooth_43.stl"
4x "pulley_toothed_43.stl"
2x "pulley_toothed_60.stl"
2x "spacer.stl"

8x 608 bearing
2x M5 washer for the outer screw (semi-optional)

There are two files for the Y carriages themselves. Both should be printed at 90+% infill for rigidity and 4+ perimeter lines for compression stability on the holes for the screws.
Print one of each.
For the Y carriage, you'll need one smooth and one toothed bearing each. Those are the "pulley_smooth_43.stl" and "pulley_toothed_43.stl" files. They should fit onto the 608 bearing well at around 100-101% scale. You can then press the bearings onto their respective place on the carriage which should be a fairly snug fit - use a screw and washer to force them down if need be.

For the front idlers, I've found it was necessary to use a larger idler than usual for the one going to the steppers on the back of the motor - otherwise, when straight, it would rub on the carriage / belt coming from the print head.
Print one of each idlers brackets, and place the 608 with their respective sleeves ("pulley_toothed_43.stl" and "pulley_toothed_60.stl") onto the mount for it - don't forget the spacer ("spacer.stl") in between to make sure the bearings can move independently.
Lastly, add the stock screw through the hole and secure it with a nut on the bottom. While it is not technically needed, I've found it lends more stability to the bearing stack than printing it solid.

You should now have a rather solid Y carriage system with decent bearings. Bear in mind that the stock 625ZZ for the wheels which ride on the aluminum profiles are now the weakest point of the system, so upgrading those for less horrible ones might be a good idea too.

Credits: Carriage layout adapted from Tronxy stock files, pulleys generated per the parametric pulley thing: https://www.thingiverse.com/thing:16627 (except for the smooth one)