They need to be torqued to a specific setting. If they're loose, the blades can be thrown, which is extremely dangerous. The required torque is 36 to 43 ft-lb (49 to 59 N·m).
To tighten them safely:
- Turn the fuel valve OFF and disconnect the spark plug cap.
- Tilt the mower onto its right side (fuel cap up).
- Wear thick leather gloves and hold the blade to prevent it from turning.
- Use a torque wrench to tighten the blade bolts to the specified range.
If you don't have a torque wrench: Do not guess. Take the mower to an authorized Honda dealer to have them tightened. You must use only Honda Genuine blade bolts and the special washers.