What are bearings and what do they do?
Bearing cartridges are responsible for the magic that enables components to move relative to each other with minimal friction whilst maintaining structural rigidity.
Bearings are responsible for the smooth rotation of wheels, cranks, headsets and suspension linkages. For more information on bearings see one of our other articles, Bicycle Bearings: Bearing Size Guide.
Why do I need to replace bearings?
Unfortunately bearings are wear components and will need replacing periodically, some of the main causes of wear are as follows:
Poor lubrication;
Debris;
Shaft & bearing misalignment;
Overloading/Loading in undesired directions;
Damage when installing.
What happens if I don't change my bearings regularly?
If bearings are neglected then they can be extremely hard to remove when the time comes.
There can be many complications, such as, bearings disintegrating and bearings seizing on shafts, all of which increases the risk of damaging components when removing the bearings.
Bearing wear also affects performance as you would expect. Rolling resistance can be increased for wheel bearings, frame/linkage bearings can negatively affect suspension performance which can change the handling characteristics of the bike for the worse.
Worn bearings can also lead to play/backlash in assemblies ("Play" is the movement of a component in a direction which is unintentional). For example, play in wheel bearings can cause the wheel to wobble side to side.
Not only is this bad for the performance and handling of the bike, making it unpredictable and dangerous, but it can also damage other components. Additional stress can be put on to the frame, wheels, forks, shock etc. Which may lead to more expensive repair costs or injury in the event of catastrophic component failure.
How do I tell when my bearings need changing?
As explained above, worn bearings often leads to play in the assembly, if you find excess play in the wheel bearings, headset, crank or suspension linkage then it's an indicator that you may want to change the bearings.
You can check for play by wiggling the components gently, it's important to remember that we don't live in a perfect world, components and assemblies are manufactured to tolerances. If you think you have found play but you're not sure because the movement is so minute then it's probably not worth worrying about!
However, the safest thing to do is disassemble the components and check the bearing by hand, rotating it with your fingers should feeling for any notchiness or play in the bearing race way which would indicate wear.
Bearings are pretty cheap and are not so hard to change, so where possible it's better to be safe than sorry and change them.
NOTE: It's always worth checking everything is tight before you point the finger at the bearing!
How do I know what bearings I need?
Identifying bearings sizes and types is pretty simple if you can get at the bearings to read the part numbers. Take a look at our article on bearing sizes for more guidance, Bicycle Bearings: Bearing Size Guide.
How do I remove my old bearings?
Here at Rotae we're conscious that most people won't have the specific tools for removing bearings, this isn't an issue, bearings being removed are destined for the bin - for recycling ;) - and so we don't care if we damage the bearings on removal.
Therefore a set of round punches and a copper and hide mallet are perfect for the job. Notice how the hammer handle is broke, that may not have been intentional but it is relevant! Excess force shouldn't be required, if you're having to really hit something hard the chances are something is wrong and you could be damaging other components.
If you're really struggling to remove a bearing there are a few tricks you can try such as:
Soaking in a penetrant such as WD-40.
Applying heat to the bearing and the component the bearing is mounted in (Area local to the bearing), but remember excess heat can damage paint work and so be careful.
If you're really stuck you can cut the bearing off, however with this method there is a high risk of damaging the components around the bearing.
This not only stops debris clashing and causing misalignment or incorrect seating of the bearing, but it also means that bearing installation required the minimal amount of force, thus reducing the risk of damage to the bearing race on installation. Further to this, it should also aid removal at the next service.
Pressing bearings
Where possible it is best to press bearings in. Damage during installation is one of the other reasons for premature wear.
As discussed previously there are specific pushbike bearing presses but these are very expensive. It may be more common for people for have bottom bracket (BB) bearing press tool and that is what we have used in the photos below in conjunction with a 1/2" drive socket. Alternatively you can apply the same method but with a vice, just ensure you protect your frame from the vice.
Using your bottom bracket press tool and an appropriately sized socket you can slowly press the bearing into its receptacle as shown.
The key things here are to take you time and make sure everything is square, the bearing should slide in relatively easily, if you find you're having to use excess force then back everything off and check alignment.
Other things to note are; when pressing the bearing in you should only be applying force to the outer race, ensure the socket isn't clashing with the frame of the bike, keep an eye on the opposite end of the bearing press tool checking it is not damaging the frame.
This technique can be applied to all bearings so long as you have access for the bearing press tool.
Tapping method
Where it is not possible to use a bearing press tool / BB tool / Vice, then you can consider tapping the bearings in with a copper & hide or Nylon mallet. The key thing here is to try and avoid damaging the bearing and keeping everything square.
This method is crude but does work, however there is increased risk of damaging the bearing, and as stated previously this can shorten bearing life.
Align the bearing with the receptacle and begin to tap, only on the out race, moving around the bearing with each tap.
You should tap gently starting at 12 O'clock and working your way around the circumference incrementally until you get back to 12 O'clock, keep repeating until the bearing is fully seated. You should stop periodically to check bearing alignment.
Normally there is a change in pitch of the noise made when tapping the bearing once it has bottomed out in the receptacle.
Post installation
Once the bearings have been installed, coat the sides of the bearing & rubber seal with grease, this will help protect the bearing cartridge from water and debris which both have a negative effect on bearing life.
How can I reduce bearing wear?
As already mentioned, bearing life can be detrimentally affected by installation damage or misalignment, however there are also other factors that can affect bearing life which are as follows:
Poor lubrication.
Debris.
Overloading/Loading in undesired directions.
How to prolong bearing life:
Avoid pressure washing bearings.
Avoid overloading - Example remove crank with a puller instead of tapping out with a mallet to save the bottom bracket bearings.
References
[1] - Upadhyay, R., Kumaraswamidhas, L. and Azam, M., 2013. Rolling element bearing failure analysis: A case study.Case Studies in Engineering Failure Analysis, [online] 1(1), pp.15-17. Available at: <https://www.sciencedirect.com/science/article/pii/S2213290212000065>.
[2] - Aditya, Amarnath, M. and Kankar, P., 2014. Failure Analysis of a Grease-Lubricated Cylindrical Roller Bearing.Procedia Technology, [online] 14, pp.59-66. Available at: <https://www.sciencedirect.com/science/article/pii/S2212017314000450>.