1. Why is cleanliness important for your bearings’ operation?
One of the most common sources of trouble in anti-friction bearings is debris that contaminates the lubrication environment. Debris can be a major cause of abrasive damage, which can lead to reduced bearing life. Cleanliness doesn’t just mean clean bearings, but instead, it can also be applied to clean housings and shafts, clean tools, clean solvents and flushing oils. It also suggests putting bearings on a clean surface and using clean rages to wipe bearings.

2. What are the benefits of proper lubrication in a bearing system?
Lubrication guards against rust, heat and friction. The lubricant reduces friction between bearing mating surfaces, helps carry away heat and protects bearing surfaces from corrosion. Whether grease or oil lubrication is used, make sure it is the proper type and grade for the application.

3. How should I store my bearings?
Don’t open the box early. Timken bearing packaging is designed to protect bearings against dirt and moisture during shipping and storage. Let the package do its job, and leave replacement bearings in their original containers. Store them in a clean, dry area until ready for use. Avoid temperature changes in you storage area – dramatic temperature swings can cause condensation and damage the bearing.

4. How important are seals to bearing performance?
Seals are vital to the performance of any bearing. Replace worn or damaged seals; they allow contaminants such as dirt and water to enter the bearing and also allow lubrication to escape. In most cases, it is a good practice to replace all seals with new ones during tear-down. A film of lubricant should be applied to the seal lip contact surface at assembly. This will help prevent seal damage during installation and at initial start-up. It also will reduce rolling torque.

5. How should I handle a bearing?
The less, the better. Fingerprints can cause rust – so handle bearings only when necessary. Never drop or handle these precision components roughly. Any sign of a bent cage renders replacement. If cleaning is required, use a cleaning solution such as kerosene or mineral spirits rather than steam or hot water. Remember, though, there are some precautions.

Never wash or clean bearings in an enclosed area. Solvent fumes are toxic and explosive. Make absolutely certain there is adequate ventilation and no open flame, welding, or smoking in the area. Wear rubber gloves to protect skin and safety glasses to protect eyes from the solvents.

6. What are some important safely considerations I should follow?
Never spin a bearing with compressed air. The rollers may be forcefully expelled, creating a risk of serious bodily harm to anyone nearby.

Do not use a hammer and/or a hardened steel bar to remove a bearing. Those tools can damage the bearing. When installing or removing bearings, always wear safety goggles, even if using a bearing puller or press. If using a mild steel bar and a hammer, fragments from the hammer, bar or bearing could be release with sufficient velocity to create a risk of serious bodily harm, including damage to your eyes.

7. How do I clean a bearing?
After a bearing has been successfully removed, it should be thoroughly cleaned to remove any dirt or contamination. To avoid corrosion, use a cleaning solution such as kerosene or mineral spirits rather than steam or hot water.

Dry the clean bearing with compressed air, directing the air stream from one end of the roller to the other while holding the cage with your thumb. When air is used to dry a bearing, make certain there is now water in the line. This eliminates the possibility of corrosion.

8. What is the difference between a standard and a precision tapered roller bearing?
The difference between a standard and a precision bearing is the bearing’s maximum total indicator rubout. The Timken Company provides four precision classes - in both metric and inch systems - covering the full range of precision application requirements.

Precision bearings are ground to very precise tolerances identified in the inch system as Class 3, 0, 00 and 000. In the metric system, precision tapered roller bearings are classified as C, B, A or AA. Typical applications include machine tools, printing presses, optical grinders, profile cutters, indexing tables and other high-precision machines.

9. How do I know which precision bearing classification to select?
The more demanding the precision objective, the more accurate the bearing must be. In rebuilding precision machines, the best practice is to install a bearing equivalent to the one the equipment manufacturer originally used.

Manufacturers of precision machines have at their disposal vast resources of engineering data and application information including skilled specialists to select the bearings and tune the critical components so these machines achieve their performance objectives.

10. Can I tell by looking at the bearing whether it is standard or precision?
Precision bearings can be identified by their packaging and by the marking on the cup and cone. If you look closely at the markings that appear on the cup and cone, you can distinguish between a standard and a precision bearing. As shown, precision bearing snot only have a stamped part number, they also have the class of precision etched on each bearing. For example, the part number is HM813810 and the class is 00.

Further identity is shown by the number 91 130. This is a serial number, which means that the bearing was assemble in 1991, and it was the 130th bearing assembly of that class and cone part number made that year. Serial numbers identify matched assemblies which must be used in sets as shipped.

11. If a precision bearing was replaced with a standard bearing, what would the result be?
If you were holding extremely close tolerances, the machine would probably produce scrap because it couldn’t turn out pieces within the tolerance limits. Excessive TIR (total indicator rubout) would cause wobble or eccentricity, a camlike movement of the spindle. This would cause the cutting tool to cut erratically and reduce the accuracy and precision of the work.

12. What do the prefixes and suffixes on a Timken® bearing mean?
Even the most common Timken bearings has dozens of variations. The letters in its prefix normally designate the duty class of the series, and the letters in its suffix designate a type of external modification from the basic part number. For example, an “M” prefix on a cup or cone part number designates a medium series. Another example is it the commonly used “CD” suffix, which designates a double cup with groove and oil holes, one of which is counter-bored for a locking pin. An explanation of all Timken bearing symbols is available from your local Timken distributor.

13. When it comes to greasing bearings, is more better?
The “more-is-better” philosophy is a common misconception about greasing bearings. It’s like taking ten aspirins for headache. Follow the specific guidelines provided in literature published by The Timken Company, and always follow manufacturers’ recommendations. These will help you lubricate just the right way…and with just the right amount. Too much grease in the bearings and housing will cause excess churning of the grease and will result in extremely high temperatures.

14. Should I use a micrometer to measure the shaft and housing every time I replace a bearing?
Absolutely. A bearing is no better than the housing it is mounted in or the shaft it is mounted on. Verifying the cone seats and housing bores are the right size is a good long-term investment. Be sure all measurements meet the manufacturer’s specifications.

15. When mounting a Timken bearing, should heat be applied?
You should never heat a standard Timken bearing more than 300 degrees Fahrenheit, and precision bearings should never be heated more than 150 degree Fahrenheit. Also, there is a tendency for the hot cone to pull away from the cold shoulder during installation. After the cone has cooled, be sure to check with a 0.002” feeler gauge to see that it is snug against the shoulder where it belongs.

16. What can I do with cones that won’t come off, even when a bearing puller is used?
Sometimes it is practical to carefully pour heated oil on the cone at the same time you’re applying pressure through a puller. The heat will expand the bearing cone and make it easier to get off.

17. I need to replace a double-row spacer bearing. Can I just replace the two single cones to avoid the expense of replacing the entire bearing?
Absolutely not. The parts must be assembled as a unit and not mixed or interchanged with parts from other assemblies. Spacer bearings are supplied as complete assemblies. Cone spacer control bearing internal clearance.

18. What type of damage will occur when there is inadequate lubrication?
Four common bearing damages will occur when there’s poor or inadequate lubrication:
a) Roller end scoring – Metal-to-metal contact from breakdown of lubricant film.
b) Cone large rib face deformation – Metal flow from excessive heat generation.
c) Total bearing lock up – Rollers skew, slide sideways and lock-up the bearing.
d) Cone large rib face scoring – “Welding” and heat damage from metal-to-metal contact.

19. Case carburized or through-hardened: which material is right for your application?
When you spec bearings, you want to be sure you choose those that are appropriate for the operating environment and technical requirements of your application. One decision you may be faced with is whether to use case-carburized or through hardened product. 

In making this decision, technical and commercial issues must be considered. Technical issues include required service life, loading, amount of debris, alignment and maintenance practices. Price and warranty are also two prime commercial considerations.

Traditionally, The Timken Company has offered only case-carburized bearing products. Case-carburized bearings have a tough, ductile core combined with a hard, wear-resistant outer surface. The core enhances the ability to endure heavy shock loads without damage while increasing debris resistance. However, there are many applications where through-hardened bearing products adequately meet performance requirements. Though-hardened bearings feature uniform hardness throughout and remain more rigid, allowing stress to reach higher levels before it is relieved. If the level of performance of case-carburized bearings exceeds the level required by the application, then through-hardened bearings may be a cost efficient alternative.

20. What sort of damage can result from foreign material being present in a bearing system?
Abrasive wear, bruising and grooving can all occur if foreign material is present. Abrasive wear consists of particle contamination; bruising is an effect of debris from other fatigued parts, inadequate sealing or poor maintenance. Grooving occurs when large particle contamination is imbedded into the soft cage material.

21. What can occur if a bearing is improperly fit?
Cone bore damage - where an out-of-round or oversized shaft fracture of the cone - results from a poor fit. A loose cup fit in a rotating wheel hub is another frequent problem.

22. What are some significant factors that limit bearing life?
Timken bearings are made and tested to provide long, dependable life. Realistically, bearings are not usually operated under controlled laboratory conditions. Excessive speed, improper load calculations, poor adjustment, improper mounting, poor sealing, inadequate lubrication, extreme conditions, and inadequate maintenance and handling practices can all significantly reduce bearing life.

23. What is etching corrosion?
Etching corrosion is caused by moisture. Condensation from humid weather can cause etching or corrosion damage. Line etching, which can be mistaken for cracks in the surface of the race or rollers, could eventually develop into premature spalling if put back in service. Bearings that are removed, cleaned and dried for inspection are often susceptible to corrosion damage. It is important that bearings be cleaned and dried properly. If they are stored, they should immediately be coated with oil or a good rust preventative and wrapped in protective paper. Bearings, whether new or used, should be stored in a dry area with low humidity.