• Buy reasonable quality motors which are inherently reliable enough for your application.
• Ensure good lubrication.
• Select correct bearings and install correctly.
• Run small spared motors to failure. Run to failure or at least imminent failure is a very respectable strategy for equipment where the consequential loss is low.
• Predicting and pre-empting failure, however cheap, is only cost effective if you can pre-empt catastrophic failure or major production loss. In general, pre-emptive actions must cost less (and probably significantly less) than the consequential loss due to failure.
• Condition monitoring can be costly and ineffective so you need to audit the effectiveness and cost effectiveness of the system.
• When motors fail, investigate to find root cause and try to eradicate repeat failure causes. (Think correct lubricant, correct lubrication regime, correct bearing, starting frequency.)
Preventive and predictive maintenance are generally sound strategies, but not universally applicable. Run-to-failure strategies are perfectly acceptable in many common situations. Maintenance strategies must be based on a rigorous understanding of the risks of failures, not on current fashions.