Can contamination occur while greasing a bearing?

Contamination can indeed occur while greasing a bearing, particularly if the fitting is dirty. When grease is applied to a bearing, any dirt, dust, or debris present on the grease fitting or the surrounding area can be introduced into the bearing itself. This contamination can lead to a variety of issues, including increased wear and tear, reduced lubrication effectiveness, and ultimately, premature bearing failure.

While it's true that old grease can also introduce contaminants and that certain processes are designed to minimize contamination, the cleanliness of the fitting is a direct and immediate factor in maintaining the integrity of the lubrication process. Ensuring that all components involved in greasing are clean and free from contaminants is crucial for prolonging the lifespan and reliability of bearings.