I was happy to see this thread.

I just got a used Geeetech Prusa i3 that the original owner assembled but apparently never got working correctly. This is my second Prusa-type printer, so I'm familiar w/the design and firmware. I've been able to get it working and calibrated.

Trouble is, I see the same problem as described above. The bearings for the X and Z rods (which actually effect the X and Y play of the extruder head) are loose on the rods. If I wiggle the bearings side to side against the rods I can see a small gap. I believe this translates to an unusual amount of wobble in the print head, since it's "multiplied" by 4 loose bearings. I don't have any looseness on my other printer.

I don't have a problem buying new bearings or rods, but how do I know which one is it?

Thanks.