Been cleaning your bearing all day with different kinds of solvent and still got dirty bearing? try the paper slip method.
What you need:
- Dirty bearing.
 - Small pieces of paper cut as shown below, must be clean.
 - Solvent/mineral spirit.
 
How you do it:
- Cut small section of paper in sharp triangular shapes, and fold it in half to increase its strength.
 - Slip the paper between two balls until it stops going any further.
 - Pinch both ends of the paper, close to the outer race.
 - Spin the outer race of the bearing, letting the paper rub the inside part of the outer race.
 - Take the dirty paper out, swap with new paper, do this until it’s clean.
 - Do this also with the inner race if necessary, most likely you don’t need to.
 - Clean the bearing with solvent/mineral spirit.
 
              