Maintenance Before Replacement. Cleaned and Greased the Dirty Wheel Bearings

Oil and grease are always used on rotating and sliding parts of motorcycles to reduce friction and lubrication. Engine oil and fork oil are changed regularly, but what about the grease in the bearings? If you turn it with your finger and it starts to rattle, it is time to replace it, but if you replace the grease in the preliminary stage, you may get better results than you can imagine.

Availability of cleaning and greasing depends on the type of bearing.

As this image clearly shows, the wheel hub is covered with dirt from brake dust, drive chain oil, and other flying particles, some of which reach the wheel bearing surface even with a dust seal. This is still a good thing because this bearing is sealed, but if it were open, the bearing grease would be directly contaminated.

This is how it looks when the dust seal, bearing, and distance collar that determines the distance between the bearing and the dust seal on either side of the wheel hub are lined up. If the lip of the dust seal wears out due to continuous contact with the wheel collar, or if the lip wears out the collar and grooves it, sealing performance is reduced, causing dirt to enter the hub.

When removing the non-contact type seal, insert a precision screwdriver or similar tool into the gap between the inner circumference of the seal and the groove of the inner ring, and remove it while being careful not to deform the core steel plate. Check to make sure that there is no roughness or gurgling by turning the bearing with the old grease remaining.

Paste grease is used to lubricate parts where liquid oil cannot be used, such as wheels and steering stems. When the lubricating part moves, the grease fluidizes and lubricates, and when the lubricating part stops, the grease returns to its paste-like state as it works. And just as engine oil deteriorates over time, grease in lubricated areas also deteriorates.
Specifically, if the structure of the thickening agent is destroyed by high mechanical pressure, high temperature, or moisture in the case of wheel bearings, the lubricating oil may become softer than its original viscosity, or the lubricating oil components in which it is mixed may liquefy.

While some riders may be aware of the need for maintenance and greasing of steering stem bearings when they feel a pull when turning the handlebars to the left or right, there may be few opportunities to be aware of greasing wheel bearings.

However, as mentioned above, the lubricating performance of grease is not permanent and will certainly deteriorate with the environment in which it is used and with the passage of time.
If the actual period of use is shorter than the design life of the bearing manufacturer, there may be no problems, but if the bearing is used for a longer period of time or in a harsh environment, the grease performance may deteriorate.

As with engine oil changes, bearing grease replacement depends on the structure of the bearing. There are three types of bearings: open, shielded, and sealed. The sealed type includes non-contact and contact types (names given are for NSK products). In the open type, the gap between the inner and outer rings is open and the retainers and balls are directly visible, allowing cleaning and greasing. In the shield type, a metal shield plate is fixed to the outer ring to close the gap between the outer ring and inner ring, and in many cases, the plate is deformed and cannot be reused if it is tried to be removed. The seal type also seals the gap between the outer and inner rings, but the seal is made of a thin steel plate with a rubber coating on its surface, which is more flexible than the shield.

However, while the non-contact type has a gap between the outer circumference of the seal and the bearing inner ring while the outer circumference is fixed to the outer ring, the contact type has a lip on the inner circumference that contacts the bearing inner ring while the outer circumference is fixed, so care must be taken not to damage the lip when removing the seal.
In the first place, shields and seals are not designed to be disassembled, and in principle, when the grease inside deteriorates, the bearing itself should be replaced. However, in practice, if they are skillfully removed and greased, it will certainly be effective.
In addition, some shielded and sealed bearings have only one side of the cover and the back side is open, so it is not unreasonable to want to remove the remaining piece to grease up the bearing.

Grease up after cleaning dirty grease.

If gravel or other foreign matter remains on the racing surface, it will cause scratches even after greasing, so grease should be washed away in the oil wash while using a brush in combination, and then carefully rinsed with parts cleaner. Blowing air to blow off the part's cleaner ingredients is effective, but if the inner ring is rotated at high speed by air in the absence of any grease, the race and ball will be damaged.

Apply urea grease, which has superior heat and water resistance compared to lithium grease. Lithium and urea are components that produce viscosity, and the lubricating component, called the base oil, is also important for grease performance. In general, high-performance synthetic oils are often used as base oils for high-performance, long-life urea greases. Chemical tuning is also possible by selecting greases with such descriptions on the product.

Contact seal type bearing in which the lip of the inner circumference contacts the groove of the bearing inner ring while the seal outer circumference is fitted and secured to the outer ring. The lip is not damaged, the core steel plate is not bent, and the removed seal is cleaned and installed in a grease-filled bearing.
The contact type is superior to the shielded and non-contact seal types in dustproof and waterproof performance, but it has high friction loss because of the contact between the seal and the inner ring.

Once the bearings have been maintained, the hubs should be cleaned at the same time. If the lip of the dust seal is worn out, replace the seal, and if the lip bites into the wheel collar and has a groove, change the orientation of the collar (for cylindrical collars without flange). This will reduce contamination inside the hub.

When greasing bearings, pre-cleaning is required, as is lubricating the drive chain. This is because new grease pushed in on top of dirty grease may not reach the bearing balls that actually need lubrication. For the open type, it is best to soak the bearings in oil wash and scrub them down with a brush before removing the respective covers for the shielded and sealed types, which are done without removing the covers. Spray-type parts cleaners can also be used, but they are time-consuming and wasteful in removing grease injected into the gap between the inner and outer rings.

When cleaning, also observe the condition of the inner and outer wheel race surfaces and balls. In the case of open-shaped wheel bearings, they may be entrapped with dust and gravel from driving. Riders who have removed the wheel and collar and looked at the bearings will understand that although the wheel hub incorporates a dust cover, it does not ensure perfect sealing. Even if there are scratches or minor damage to the racing surface, the viscosity of the grease acts as a buffer, and since tires rotate under heavy vehicle weight, riders often do not notice any abnormalities in the wheel bearings, but if the bearings are left alone and even the grease is washed off, the rotation may not be smooth and you may feel a skinny If the bearing is left alone and the grease is washed out, the rotation may not be smooth and you may feel a grinding sensation. In such cases, replace the bearing with a new one instead of reusing it.

If there is nothing wrong with the bearing itself, it may be possible to tune it by injecting new grease. The grease is classified into calcium, lithium, urea, and other types according to the type of thickening agent that gives viscosity to the bearing, with the latter type having higher performance. Furthermore, there is a standard called "viscosity," which indicates softness, similar to the viscosity of engine oil. The smaller the number indicating the degree of consistency, the softer the grease, and if the lubricant performance is the same, there is the advantage of lower friction loss. There is no need to worry about using multi-purpose grease anywhere, but there are some riders who choose grease thickness very carefully in order to reduce friction loss in motorsports such as racing machines.

Although it may be a minority to be so particular, cleaning the old grease and filling it with new grease will noticeably lighten the rotation of the tires, just as when the drive chain is lubricated or suspension links are greased. Some people may think that it is quicker to replace the bearings without such troublesome work, but from the viewpoint of extending the life of usable parts further, cleaning and greasing the bearings is effective.