How to Service BMX Bearings

Servicing BMX bearings means checking the bearings in your hubs, bottom bracket and headset, then cleaning and regreasing them or replacing them when they are worn. Most modern BMX bikes use sealed cartridge bearings, which are often replaced rather than rebuilt. Some cheaper or older bikes use loose ball bearings, which can be cleaned, regreased and adjusted.

See bearings for how bearings work and the common types.

Sealed cartridge vs loose ball

Feature	Sealed cartridge	Loose ball (cup and cone)
How it is built	Balls held between inner and outer races in one sealed unit	Separate balls run between a cup and a cone
Where on BMX	Most hubs, Mid and Spanish bottom brackets, integrated headsets	Cheaper hubs, many American bottom brackets, older headsets
Adjustment	None, fit and forget	Needs adjusting for play
Service	Clean and regrease or replace	Strip, clean, regrease, adjust
Replacement	Swap the whole cartridge	Replace balls, and cups or cones if pitted

Signs a bearing needs attention

• Rough or crunchy feel. Turn the part slowly by hand. A good bearing feels smooth.
• Play. Grab the wheel, crank arm or fork and rock it side to side. Movement or a knock means play.
• Noise. Clicking, creaking or grinding while riding.
• Slow spin. A wheel that stops quickly when spun by hand, with the chain off.
• Rust or water. After riding in the rain or washing with a hose.

Check one area at a time so you know which bearing is the problem.

Tools and supplies

• Allen keys and spanners for your axle nuts, bolts and cranks
• A small pick or thin blade for lifting bearing seals
• Bearing grease (a proper bicycle or bearing grease)
• Degreaser or solvent for cleaning
• Clean rags and gloves
• A cone spanner for loose ball hubs
• A bearing press or suitable drifts for removing and fitting cartridges
• Replacement bearings in the correct size

The size of a sealed bearing is usually printed on the seal as a code (for example, a four digit code such as 6903 or 6803). Match the code exactly. If you cannot read it, measure the inner diameter, outer diameter and width, or take the old bearing to a shop.

How to service a sealed cartridge bearing

You can often service a sealed bearing without removing it from the part.

1. Remove the part. Take out the wheel, cranks or fork as needed so you can reach the bearing.
2. Remove any dust caps or spacers. Note the order as you go. A photo helps.
3. Spin the bearing by hand. If it is rough, notchy or has play, skip to replacement.
4. Lift the seal. Gently slide a pick or thin blade under the inner edge of the rubber seal and lift it out. Work slowly so you do not bend it. Some bearings have metal shields that are not designed to come out. Leave those in place.
5. Clean out the old grease. Wipe away dirt and flush with a small amount of degreaser. Let it dry completely.
6. Check again. Spin the clean bearing. If it still feels rough, replace it.
7. Regrease. Pack fresh grease into the bearing, filling the space between the balls without overpacking.
8. Refit the seal. Press it back gently and evenly by hand.
9. Reassemble. Refit spacers, caps and the part, then tighten bolts to the maker's recommended torque.

How to replace a sealed cartridge bearing

1. Remove the axle, spindle or fork. Follow the maker's instructions for your hub, bottom bracket or headset.
2. Drive or press out the old bearing. Use a bearing puller or a drift on the inner race. The old bearing is usually damaged by removal, so do not reuse it.
3. Clean the seat. Wipe out the hub shell, BB shell or headset cup. Check it for damage.
4. Grease the seat lightly. A thin film helps fit and stops corrosion.
5. Press in the new bearing. Push only on the outer race when pressing into a shell. Push only on the inner race when fitting onto an axle or spindle. Keep it square and do not hammer on the seal.
6. Refit spacers and the axle or spindle. Check that everything spins freely with no binding.
7. Reassemble and torque. Follow the manufacturer's torque figures.

Pressing on the wrong race can damage a new bearing before you ride it. If you do not have a press, a bike shop can fit bearings quickly.

How to service loose ball bearings

Hubs (cup and cone)

1. Remove the wheel.
2. Loosen the locknut on one side. Hold the cone with a cone spanner and undo the locknut.
3. Unscrew the cone and remove the axle. Catch the balls in a rag. Count them.
4. Clean everything. Clean the balls, cups, cones and axle.
5. Inspect. Look for pitting, grooves or rough tracks on cups and cones. Replace damaged cones and balls. Pitted cups often mean a new hub.
6. Regrease. Put a layer of grease in each cup and press the balls into it. Use new balls of the same size and number.
7. Refit the axle and cone. Screw the cone in until it just touches the balls.
8. Adjust. Back it off until the axle spins freely with no play. Lock the locknut against the cone while holding the cone still.
9. Check. Refit the wheel and recheck for play once the axle nuts are tight.

American bottom brackets and loose ball headsets

The idea is the same: strip, clean, inspect, regrease and adjust so there is no play and no tightness. Caged ball retainers usually face a particular way. Note the orientation before removal, or follow the maker's instructions.

Hubs, BB and headset tips

• Hubs. Rear hubs carry the most load, especially on cassette and freecoaster hubs with driver bearings. Follow the hub maker's service guide, because internal layouts differ.
• Bottom bracket. Crunching or knocking through the pedal stroke is often the BB. Check crank bolts are tight first. See cranks.
• Headset. A knock when braking or a notchy feel when steering points to the headset. Check stem and top cap adjustment before replacing bearings.

How often to service

There is no fixed schedule. Riding in wet weather, washing with high pressure water and dusty dirt riding all shorten bearing life. A quick check during your weekly BMX maintenance basics routine catches most problems early. Avoid pointing a hose or pressure washer at hubs, the BB or the headset.

Related

• Bearings
• Bottom bracket
• Headset
• Front hub