After reviewing a few well-respected lubrication texts and speaking with two well-known bearing manufacturers, we conclude that there is no recognized standard with which to make a decision to disassemble and repack a bearing. The second part of the question is about whether there is a standardized approach for making this decision. If the bearing cannot be configured with a Zerk and a relief, and a “clean and repack” event is the only option, then scheduling the activity becomes a judgment call based on a multitude of factors as noted below. When the bearing is replenished according to sound engineering principles (right product quality, right product selection, right amount, right frequency, no cross-contamination, etc.), the bearing does not require disassembly, cleaning and repacking to maintain lubricant and bearing health. If a bearing is intended to be grease-lubricated, then it would be best to include a Zerk or similar fitting to enable replenishment without opening the bearing cavity. The first issue is if/when to repack a bearing.
We should look at the issue as a two-part problem. However, if circumstances exist where this must be done, then some thoughtful planning is justified. Simply stated, the benefit practically exceeds the costs and risks. Given the practical challenges of hand-packing a bearing with any hope of maintaining grease and bearing cleanliness, it is often best to avoid opening a bearing to clean and repack.
"Is there a standard method for determining if and when a bearing should be cleaned and repacked?"