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Overheated bearings

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The Fan doctor - Overheated Bearings

Ball or roller bearings tend to heat up when they have been over greased and will cool down to their normal running level when the excess grease oozes out. The normal operating temperature of a bearing may be well above 60 degrees C which is hot to touch. Temperatures above this have to be read with instruments and anything above 90 degrees C should be questioned. If you place a drop of water on the bearing and it sizzles, the bearing is in distress and should be changed before it seizes and ruins the shaft.
Bearings may be worn and failing
1. Replace the bearings. Remember to also check the shaft. (refer back to noise section)
Improper grease
1. Use a lithium base, high speed, channeling type grease. Do not use high temperature or general purpose grease.
Over greasing
1. If you allow the bearing to run for a few hours, it will normally purge itself of the extra grease. You can simply remove excess grease from split roller bearings by lifting the top half of the block for access.
Bearing exposed to "heat soak" from an oven or dryer after shut down
1. "Heat soak" occurs when a fan is idle and its shaft cooling wheel can no longer cool the inboard bearing. Heat from inside the fan can actually cook the grease. A 15 minute fan run after the oven heat is turned off will cool the fan shaft and protect the bearing.




Loose V-belts may cause belt slippage and friction heating resulting in hot bearings, shafts or sheaves.
1. Tighten belt to proper tension. A good rule of thumb - you should be able to depress the belt the same distance as the thickness of the belt.

Excessive V-belt tension
1. Belts may be too tight. Adjust to the correct tension.

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