27.2. Main rotor shaft bearings

Some helicopters (ECO, etc) have open-faced bearings. These bearings are not sealed, and because the ball-bearings are exposed, they can become contaminated with dirt and grit.

If you notice the main rotor shaft bearings grinding or not rotating smoothly, then they should be removed and cleaned in some good solvent or cleaned with compressed air. If they still sound or feel funny, they should be replaced.