Bearing storage, fits, clearance and mounting: the basics
Most early failures are made before start-up. A single checklist for storing, preparing and fitting a bearing.
Storage and transport
Store bearings in a cool, dry place out of sunlight, off the floor by at least 30 cm and away from large temperature swings that cause condensation and rust. Do not over-stack. Use first in, first out. Never roll a bearing on the floor, and lift heavy ones with proper equipment.
Before fitting
Unpack only at the last moment, in a clean, dry area. Handle with clean gloves. Rust preventive on a new bearing is normally compatible with common lubricants and the bearing can be used without washing; high speed and precision bearings may be cleaned with fresh kerosene using a low-pressure spray or separate wash baths with a raised mesh bottom. Cover them after cleaning. Pairs of angular contact or tapered bearings should come from the same lot with the direction marks matched.
Check the shaft and housing
Measure and record size, roundness, taper, surface roughness, shoulder squareness and corner radius, and look for nicks and burrs. Rough surfaces under oil seals wear them out. Check split housings for distortion from uneven bolt tightening.
Fit and clearance
The shaft to inner ring fit and the housing to outer ring fit decide the interference and loose fits. Normal conditions are an interference fit on the shaft, a loose fit in the housing and 5 to 10 degC difference between rings. The clearance reduces by about 80 percent of the interference amount when the inner ring is fitted on a shaft, so choose the clearance group for the operating clearance you want and check it after mounting. Too small a clearance heats and wears; too large makes noise and vibration.
| Mounting method | Practice |
|---|---|
| Press fit | Use a dolly sized for the ring, press gently and evenly, and push only on the ring being fitted |
| Thermal expansion | Heat the inner ring only as much as needed, and mount quickly |
| Adapter or withdrawal sleeve | Follow the sleeve procedure and check clearance reduction |
Lubrication and trial run
Grease at the rated quantity and run the machine; watch vibration, noise and temperature. Oil changes depend on temperature: about annual at 50 degC, more often above 100 degC. Excess grease causes churning heat; open the relief hole if there is one.