How much grease does a bearing need, and how often?
Both too little and too much grease damage a bearing. Here are the rules of thumb for the quantity, the interval and the mistakes to avoid.
Initial fill
Fill the bearing completely, and fill the housing only partly: about 30 to 50 percent of the free space in the housing, depending on speed. Higher speeds need less, because the bearing churns the grease and heats up when the housing is packed full.
Relubrication quantity
A widely used rule of thumb for the grease to add each time is G = 0.005 × D × B, with G in grams, D the bearing outside diameter in mm and B the bearing width in mm.
| Example | D | B | G = 0.005 × D × B |
|---|---|---|---|
| Deep groove ball bearing 6309 | 100 mm | 25 mm | about 12.5 g |
| Spherical roller bearing 22218 | 160 mm | 40 mm | about 32 g |
How often
The interval depends on speed, bearing size, bearing type, grease and temperature. Two rules of thumb help you adjust a starting interval:
- Above about 70 °C, the interval roughly halves for every 15 °C increase.
- Heavy contamination, vibration or wet conditions shorten it, often by half or more.
Signs of too much grease
- The bearing runs hotter after greasing, then settles.
- Grease is forced through the seals.
- Grease has softened or darkened from churning.
Signs of too little grease
- Rising temperature and noise between greasing.
- Dry, dark or hardened grease in the housing.
- Smeared or discoloured raceways at inspection.
Apply it properly
- Grease while the bearing is turning, if it is safe, with the drain open so old grease can leave.
- Use a grease meter or an automatic system, so the quantity is measured and not guessed.
- Do not mix greases with different thickeners without checking compatibility.
Questions
How much grease should I put in a bearing?
Fill the bearing completely and the housing about 30 to 50 percent, then add roughly G = 0.005 × D × B grams at each relubrication, with D and B in millimetres.
What happens if I put too much grease in a bearing?
The bearing churns the grease, runs hotter, and may push grease through the seals. Over-greasing is one of the common causes of early failure.
How often should bearings be greased?
It depends on speed, size, temperature and conditions. The interval shortens at higher temperatures and in dirty or wet conditions, so use a calculator rather than a fixed calendar.
Can I mix different greases?
Only if their thickeners are compatible. Mixing incompatible greases can soften or harden the grease and cause failure, so check a compatibility chart or purge the old grease.