Which symptom most strongly indicates a loose or failing bearing in a generator?

• A. Decreased vibration with cooler bearings.
• B. Increased vibration, unusual noise, and rising oil temperature.
• C. No vibration change but louder electrical noise.
• D. Oil leaks only without vibration changes.

Answer: (B)

When a bearing is loose or failing, it can no longer support the rotating shaft smoothly, which immediately shows up as more vibration. That vibration often comes with audible irregularities or unusual noises as the shaft and bearing rub and wobble, and the increased friction and compromised lubrication tend to drive the oil temperature up. This combination—strong vibration, unusual noise, and rising oil temperature—is a clear, reinforcing sign that the bearing health is deteriorating.

Other options don’t match the symptom pattern you’d expect from a bearing problem: diminished vibration with cooler bearings would imply the opposite of a failing bearing; no change in vibration but louder electrical noise points to electrical issues rather than a mechanical bearing fault; oil leaks alone don’t necessarily indicate a failing bearing, though they can accompany other faults. The trio of increased vibration, unusual noise, and rising oil temperature most strongly points to a loose or failing bearing.