Bearings support moving parts while controlling friction and keeping components aligned. Two broad types are plain bearings, which slide against a surface, and rolling-element bearings, which use balls or rollers. This guide explains how to recognize, compare, choose, and handle each type. Before working on machinery, identify the equipment and bearing specifications, consult its service manual, and isolate power so parts cannot start unexpectedly.
What You’ll Need
- The equipment manual, parts list, or bearing identification markings
- A clean, well-lit work area and a way to keep removed parts in order
- Safety glasses and suitable gloves; avoid loose clothing around rotating equipment
- If inspecting a bearing: basic cleaning materials and a suitable lubricant specified by the manufacturer
- If removal or installation is required: the correct puller or press tools and any specified measuring tools
Step-by-Step
- Make the equipment safe. Switch it off, disconnect and lock out its power source, and follow the manufacturer’s procedure for stored energy. Let hot components cool. Support suspended or spring-loaded parts before removing a bearing. Never put fingers near a bearing while a shaft or wheel can move.
- Find the bearing’s job and location. Bearings may support a rotating shaft, wheel, hinge, or other moving part. Use the parts diagram or service manual to find the exact component. A machine can contain several bearing designs, so do not assume every bearing on it is the same type.
- Identify a plain bearing. A plain bearing has no rolling elements. A shaft or other surface moves directly against a bearing surface, often through a thin film of lubricant. Plain bearings may look like a sleeve, bushing, washer, or lined block. They are common in simple pivots, low-profile assemblies, and applications where quiet operation or resistance to shock is useful.
- Identify a rolling-element bearing. This type has balls or rollers between inner and outer raceways. The rolling elements may be visible, or enclosed by seals or shields. Common examples include ball bearings, cylindrical roller bearings, and tapered roller bearings. The manufacturer’s part number is more reliable than appearance alone, especially when the bearing is sealed.
- Compare the operating conditions. Check the load direction and size, shaft speed, available space, temperature, contamination, vibration, and maintenance access. Plain bearings can suit sliding or oscillating motion and may tolerate shock loads, but need the right material, clearance, and lubrication for the application. Rolling-element bearings generally provide low rolling friction and accurate shaft support, but their capacity, speed limits, and contamination resistance depend on their design.
- Confirm the exact specification. Read markings and check dimensions, material, internal clearance, seals, lubrication, and load rating against the manual. A bearing that fits physically may still be wrong for the speed, load, temperature, or duty cycle. Do not select a replacement based only on its outside diameter or a generic label such as “ball bearing.”
- Inspect without damaging the bearing. Look for cracks, scoring, corrosion, discoloration from heat, contamination, and looseness. A rolling bearing should turn smoothly by hand when it is removed and safe to handle; roughness or noise is a warning, not a measurement of its remaining life. Inspect plain bearings for uneven wear, grooves, loss of lining, or excessive clearance. Do not spin a bearing with compressed air.
- Choose the right type only when the design allows it. If a manufacturer specifies a particular bearing type, size, material, fit, and lubricant, use that specification. Switching between plain and rolling-element bearings is a redesign, not a like-for-like repair: the shaft, housing, clearances, lubrication, and load paths may all need changes. Ask a qualified technician or bearing supplier if the original specification is unavailable.
- Service or replace according to instructions. Keep parts and work surfaces clean. Use only the specified lubricant and quantity; excess grease can cause heat, while incompatible grease can damage a bearing. For removal and installation, use the specified tools and apply force only to the ring or surface intended by the manufacturer. Never hammer directly on rolling elements, raceways, or a bearing seal.
- Reassemble and check operation. Refit seals, spacers, retainers, and fasteners in the documented order and tighten them to the specified torque. Restore guards before reconnecting power. Run the equipment as directed, then check for abnormal noise, vibration, temperature, leakage, or binding. Stop immediately if anything seems wrong, isolate power again, and investigate rather than forcing it to run.
Common Mistakes
- Confusing a bearing type with a particular product. Plain and rolling-element are broad categories; dimensions, materials, seals, and load capacities still matter.
- Replacing by appearance alone. Seals can hide rolling elements, and some plain bearings have complex liners. Verify the part number or engineering specification.
- Assuming grease fixes every problem. A worn, contaminated, damaged, or incorrectly fitted bearing may need replacement. Adding lubricant can mask symptoms briefly without correcting the fault.
- Mixing lubricants or over-lubricating. Follow the specified lubricant type and amount. If compatibility is uncertain, do not combine products; check the manual or supplier.
- Forcing a bearing into place. Misalignment, wrong fits, and force applied through rolling elements can cause immediate damage. Stop if installation does not proceed as specified.
- Ignoring the cause of failure. Misalignment, loose housings, contamination, overloading, and incorrect lubrication can quickly damage a replacement bearing.
Tips
- Photograph the assembly before disassembly and label parts so spacers and seals go back in the right order.
- Record the bearing’s full markings, including suffixes; small differences can indicate a different seal, clearance, or internal design.
- Keep replacement bearings in their packaging until installation, and avoid touching precision surfaces with dirty hands.
- Use a clean, lint-free cloth for inspection. Do not wash a sealed bearing or remove its seals unless the manufacturer says it is serviceable.
- Check alignment and the condition of the shaft and housing during replacement. A new bearing will not compensate for damaged mating parts.
Troubleshooting
The bearing is noisy, rough, or hot: Stop the machine and isolate power. Check for contamination, incorrect or insufficient lubrication, misalignment, excessive load, and improper fit. Do not keep operating it to see whether the noise goes away. Replace a damaged bearing and correct the underlying cause.
The replacement will not fit: Compare its complete part number and measured dimensions with the original specification. Check for a burr, dirt, a damaged shaft, or a distorted housing. Do not grind or hammer the bearing to make it fit; obtain the correct part or have the fit assessed.
A plain bearing wears quickly: Check shaft finish, alignment, clearance, material compatibility, load, and lubrication method. Confirm that the specified lubricant reaches the bearing surface and that abrasive dirt has not entered.
A rolling-element bearing fails soon after replacement: Look for installation damage, incorrect preload or clearance, a poor fit, contamination, excessive load, or a shaft or housing problem. Follow the equipment manual and seek qualified help if the cause is not clear.
Frequently Asked Questions
What are the two main types of bearings?
Two broad types are plain bearings, where surfaces slide against each other, and rolling-element bearings, which use balls or rollers between raceways.
Which bearing type is better?
Neither is universally better. The right choice depends on load, speed, motion, space, environment, lubrication, service life, and the equipment design.
Are sleeve bearings plain bearings?
Yes. A sleeve bearing, often called a bushing, is a common plain-bearing design in which a shaft runs inside a sleeve-shaped surface.
Are ball bearings the same as rolling-element bearings?
Ball bearings are one kind of rolling-element bearing. Other kinds use rollers, such as cylindrical, needle, or tapered rollers.
Can I replace a plain bearing with a ball bearing?
Not as a direct substitution unless the equipment is designed or approved for it. The change can affect fits, loads, alignment, lubrication, and safety.
How can I tell whether a bearing needs replacement?
Follow the maker’s inspection limits. Abnormal noise, roughness, heat, visible damage, or excessive play can indicate a problem, but first make the equipment safe and check the cause.