The fundamental principle of efficient lubricant is to make a store lubricant film which prevents metal to contact of the sliding parts of the bearing most effectively and economically, and thus prevent wear resulting from this under operating conditions .It also reduces the rolling frication by keeping the elements and tracks neat. It also minimizes the bearing noise and prevents corrosion. Ball and roller bearings can be lubricated with either oil or grease, depending on operating conditions.
For high speed operations and in long horizontal steam engine bearings, oil lubrication is considered to be far better than grease since it possesses high tackiness and reduces the friction. The oil should be fed regularly in small amounts, in order to keep the bearing temperature down . For moderate and low speeds, oil pump lubrication system is adopted, in which housing is filled up to the level of the center of the lowest ball or roller. Only height grade non-aging mineral oils should be used, which are completely free from all mechanical impurities. Checking the oil viscosity that it is suitable for the working temperature is very essential
On account of simplicity of maintenance and sealing of prevent entry of dirt, grease lubrication is widely used. The grease selected should have minimum possible adhesive properties so that it adheres well to metal. It is modern practice to use any lithium base or calcium base grease.