Too Much Lubricant

A very common error in maintenance of machinery is the tendency to over-lubricate. If the bearing reservoir is kept constantly full of grease, the friction heat developed within the lubricant will cause its own rapid deterioration.

How Much Grease

There is no set formula to determine the exact amount of grease necessary to lubricate a bearing because the quantity is directly dependent upon such factors as the application, the bearing and retainer design and the type of grease used. Certain bearing of the high precision types used in high speed applications may have as little as 20 percent of the bearing void filled with grease. Other bearings of the types used in low speed applications may have as much as 80 percent of the bearing void filled with grease. Aircraft bearings of the oscillating types may be 100 percent filled with grease. Even within the limits of a given application, the quantity of grease may be dependent upon the type of grease selected. For example, two different grades of grease, one a NLGI Grade #1 and the other a NLGI #4, have proved to be suitable lubricants for machine tool spindle bearings. However, because the Grade #1 grease has a tendency to churn, a lesser amount must be used in a given bearing as compared to the amount of Grade #4 grease is a channeling type which does not churn; consequently, the amount used in the bearing is less critical. Over greasing may cause a rapid temperature rise in the bearing that can damage both the lubricant and the bearing. The bearing manufacture should be contacted when you are unsure of the amount of grease or oil for proper lubrication. In standard applications, it is generally recommended that the bearing should be greased one-third to one half full.