A noob question about bearings

I have a Prusa I3 (HE3D-Xi3)
I printed some replacement bed bearings because as I'm sure everyone knows the metal ones are quite noisy.
Question is:
What is the best way to fasten everything back down without the bearings binding and being very difficult to move?
One at a time they slide on the guide rail as smooth as silk. When I attach them to the bed they start binding even
loosely attached. I've been trying several things but just not the right thing.
Any suggestions would be seriously appreciated.

Sounds like it could be a retrograde step, what about grease are you using any, are they for 8 or 12mm rod, have you tried the longer bearings, much better than the short ones.