More bearings fail from the wrong amount of grease than from the wrong grease. Too little, and the bearing runs dry. Too much, and it churns, overheats and pushes out its seals. The fix is not complicated: a simple formula for the quantity, a sensible interval and a calibrated grease gun.
For relubrication from the side of the bearing, use G = 0.005 × D × B, where G is grease in grams, D is the bearing outside diameter in mm and B is its width in mm. For relubrication through the outer ring, use about 0.002 × D × B. Set the interval by speed, size and temperature, and halve it for every 15 °C above 70 °C.
| Situation | Formula (grams) |
|---|---|
| Relubrication from the side of the bearing | G = 0.005 × D × B |
| Relubrication through the outer ring (groove and holes) | G = 0.002 × D × B |
D and B are in millimetres and are found in the bearing catalogue from the bearing number.
| Bearing | D × B (mm) | Grease per shot (from the side) |
|---|---|---|
| 6205 (small motor) | 52 × 15 | about 3.9 g |
| 6316 (large motor or fan) | 170 × 39 | about 33 g |
| 22220 (spherical roller, conveyor or crusher) | 180 × 46 | about 41 g |
Your team counts strokes, not grams. So calibrate each gun once:
At 1.5 g per stroke, the 6316 bearing above needs about 22 strokes, not "a couple of pumps".
The interval depends mainly on:
Bearing makers publish charts that combine speed and size into a base interval. Electric motor makers often print the grease quantity and interval on the motor nameplate; follow them where available.
Use the maker's interval as the start. Then watch the bearing: temperature, noise and the condition of purged grease tell you whether to shorten or stretch it. An ultrasonic grease gun or detector makes this much more precise.
Overgreasing deserves its own warning; read why overgreasing can damage bearings.
For a new or cleaned bearing, fill the bearing itself completely, and fill the housing only partly. For normal speeds, a fill of about 30–50% of the free housing space is common; high-speed bearings need less. Too much in the housing causes churning and heat.
How many grams of grease does a bearing need?For relubrication from the side, use 0.005 × outside diameter (mm) × width (mm). For a 6205 bearing that is about 4 g; for a 22220 it is about 41 g.
How many pumps of a grease gun is one gram?It depends on the gun; many manual guns give between 1 and 2 g per stroke. Weigh 10 strokes to find yours.
How often should motor bearings be greased?Follow the motor nameplate or manual. Without it, base the interval on speed, size and temperature, and shorten it in hot, dusty or vibrating conditions.
Is it bad to grease a bearing too often?Yes, if each shot is large. Frequent small shots of the right size are better than occasional large ones, but too much total grease causes heat and seal damage.
Send us a list of your main bearings with sizes, speeds and temperatures, and our team will help you work out quantities and intervals.