How to Maintain a Bearing

Seals and shields

What’s the difference between ZZ and 2RS bearings?

ZZ (also called 2Z) bearings have a metal shield on each side. The shields don’t touch the inner ring, so they create very little friction and suit higher speeds. They keep out larger debris but offer less protection against fine dust and water.

2RS bearings have a rubber seal on each side. The seals touch the inner ring, which gives better protection against water and dirt but adds a little friction and lowers the maximum speed.

Seal and shield codes vary between manufacturers. For example, NSK uses DDU and VV, NTN uses LLU and LLB, and SKF uses 2RS1 and 2RSH. If you’re unsure what your bearing has, contact us with the full part number.

Can I buy replacement seals or shields?

Seals and shields are generally not sold separately, as they are specific to each manufacturer and bearing size. If a seal or shield is damaged, we recommend replacing the bearing.

Greasing

Do sealed or shielded bearings need regreasing?

Usually not. Bearings with seals or shields on both sides are packed with grease at the factory and are designed to be “lubricated for life”. When the grease wears out, the bearing is normally replaced rather than regreased.

My housing has a grease nipple, but my bearing has shields on both sides. Will the grease reach the bearing?

Very little will. Shields and seals are designed to keep grease in and dirt out, so they also block most of the grease coming from the housing. You have two options:

• Use a bearing with one shield or none. A single-shielded or single-sealed bearing, or an open bearing, lets grease in from the open side. Fit it with the open side facing the grease supply.
• Remove the shield or seal facing the grease supply. See the next two questions.

If you’re unsure which bearing suits your housing, contact us with the housing part number and we can advise.

How do I remove a metal shield from a bearing?

Most metal shields are pressed into a groove in the outer ring and are not designed to come out. To remove one:

1. Clean the bearing face so no dirt can fall inside.
2. Insert a small flat screwdriver or pick into the gap between the shield and the inner ring.
3. Lever the shield gently outwards until it pops free, working around the edge if needed.

Take care not to touch the balls or the cage. The shield will bend during removal and usually cannot be refitted, so only remove the shield on the side facing the grease supply.

How do I remove a rubber seal from a bearing?

Rubber seals can be removed more gently than metal shields:

1. Clean the bearing face.
2. Slide a thin blade or pick under the outer edge of the seal, where it meets the outer ring.
3. Lift the seal carefully out of its groove.

A seal removed this way can sometimes be pressed back in, but the sealing lip is easily damaged. If the seal is torn or distorted, it will no longer keep dirt out.

Do pillow block and flange units need the seals removed to grease them?

No. Housed units such as UCP, UCF and UCFL usually use inserts with a lubrication hole in the outer ring, so grease from the nipple goes straight into the bearing. Leave the seals in place.

How do I grease a bearing?

Wipe the grease nipple clean before connecting the grease gun, so you don’t push dirt into the bearing. If it’s safe to do so, apply the grease slowly while the shaft is turning, as this helps it spread evenly.

Stop when you see fresh grease appear at the seal or relief point, or once you’ve added the recommended amount. Use the same type of grease that’s already in the bearing, as mixing incompatible greases can cause them to break down.

How much grease should I add?

Less than you might think. Over-greasing causes heat, which breaks down the grease and can damage seals. As a guide:

• Greasing from the side of the bearing: grease (g) = 0.005 × outside diameter (mm) × width (mm)
• Greasing through a hole in the outer ring, as on most pillow block inserts: grease (g) = 0.002 × outside diameter (mm) × width (mm)

For example, a 6205 bearing (52 mm outside diameter, 15 mm wide) needs about 4 g from the side, or about 1.5 g through the outer ring.

How often should I regrease a bearing?

This depends on speed, temperature, load and how dirty the environment is. Check the equipment manufacturer’s recommendations first. As a rough rule, high speeds, high temperatures and wet or dusty conditions all mean more frequent regreasing.

Inspection and replacement

How do I know when a bearing needs replacing?

Most bearings give warning signs before they fail. Look out for:

• Grinding, rumbling or clicking noises
• Running noticeably hotter than usual
• Increased vibration
• Play or looseness in the shaft
• Grease leaking out or looking dark and contaminated
• Rust or visible damage to the seals or shields

Can I clean and reuse an old bearing?

Open bearings can be cleaned and relubricated if they show no wear or damage. Sealed and shielded bearings cannot be cleaned properly without removing the seals or shields, so they should be replaced.

Fitting and storage

How should I fit a new bearing?

Press only on the ring that has the tight fit. That’s the inner ring when fitting onto a shaft, and the outer ring when fitting into a housing. Use a fitting tool or a sleeve that sits flat on the correct ring.

Never hammer the bearing directly or apply force through the balls, as this can dent the raceways and shorten the bearing’s life. Keep the bearing clean and in its packaging until you’re ready to fit it.

How should I store bearings?

Keep bearings in their original packaging, lying flat, in a clean, dry place at room temperature. Avoid areas with vibration, as this can damage a bearing even when it isn’t running.

If you’re unsure which size you need, see our Deep Groove Ball Bearing Size Chart or provide the measurements, and we’ll help identify the correct size.

Browse our range of bearings.