How to Grease Bearings | A Proper Greasing Guide

Grease bearings by cleaning out old grease, then applying the correct type and amount so it reaches all rolling elements and cages.

Doing this well prevents premature wear, overheating, and costly downtime. The goal is to replace old, contaminated grease while ensuring fresh grease coats every working surface. The process differs slightly depending on whether you’re greasing an open bearing before installation, a mounted unit, or a split housing, and getting the quantity right matters just as much as the technique.

How Much Grease Should a Bearing Get?

Quantity is the most common mistake. Too little grease means parts run dry; too much creates heat and pressure that can damage seals.

Some low-speed applications prone to contamination may use up to 90% of the housing free space. The grease must reach all rolling elements and cages — coating the outside of the bearing isn’t enough.

For open bearings being greased before mounting, you’ll fill the free space between the rolling elements and the cage from both sides, ideally using a grease packer. Larger bearings should be stabilized with chocks or a v-block on a clean plastic sheet. If the bearing isn’t mounted immediately, wrap it in plastic to keep contamination out.

Greasing a Pillow Block and Split Housings

That escaping grease is your cue that the bearing is full. Excessive pumping pressure can damage the seals, so go steadily rather than forcing it.

Split housings require a fuller procedure. Start by cleaning the work area, then open the housing and remove all used grease from the cavity. Clean the cavity with solvent, and clean and dry the bearing itself. Fill the bearing’s free space with grease from the accessible side, refill 30% to 50% of the housing with grease, close the housing, and run the bearing in. Relubrication should always be done while the bearing is warm from operation and rotating, if it’s safe to do so.

What Happens if You Mix Grease Types?

Mixing greases can cause the thickener system to break down, leading to lubrication failure. Before applying a new grease type, remove as much old grease as possible.

SKF’s guidance is specific: if the new grease is incompatible with the old grease, or if the old grease contains PTFE thickener or is silicone-based, the bearing should be thoroughly washed with an appropriate solvent. If mixing is unavoidable, the base oil should be the same, the thickener types should match, and base-oil viscosities shouldn’t differ by more than one ISO VG class. Consistency should also be identical — the same NLGI class.

Bearings operate at different speeds, temperatures, and loads, and choosing the right grease starts with deciding between grease and oil. For grease selection itself, the primary parameters are speed, temperature, and load.

Running In and Temperature Limits

Freshly greased bearings shouldn’t be run at full speed immediately. Running the bearing slowly lets the grease distribute evenly and allows excess to escape.

Super-precision bearings operating at high speeds are the one exception to the general fill guidance — they should have less than 30% of the free bearing space filled with grease. Old grease must always be allowed to leave the bearing unhindered, so relubrication should continue until a fresh collar of grease appears at the seal gaps. If you’re choosing a grease for a specific application, our roundup of the best grease for bearings compares top options by operating conditions. SKF’s selection guidance on selecting a suitable grease explains how those parameters map to specific products.