Most ball bearings in wheels, gearboxes and some crankshafts are standard parts with a number stamped on the side. A bearing supplier can sell the same bearing from the number, often for much less than the bike maker's part, and it does not matter much which country made it if it comes from a reliable supplier. If the number has worn off, three measurements identify it instead. This page shows how to read the number and the letters after it, and how to measure.
Safety
- Wear eye protection when you clean a bearing with solvent or compressed air.
- Do not spin a dry bearing fast with compressed air. It can break apart.
You need
- A vernier caliper.
- A torch and a magnifier for faint numbers.
- Solvent and a rag.
Steps
- Clean the side of the bearing and read the number on the outer or inner ring. Write it down exactly, including every letter.
- Read the series. In common metric bearings the first digit 6 means a single row deep groove ball bearing. The next digit gives the series: 60 is light and thin, 62 is medium, 63 is heavier. A 6202 and a 6302 have the same bore but different outside size and width, so they do not swap.
- Read the bore code (the last two digits). 00 is a 10 mm bore, 01 is 12 mm, 02 is 15 mm, 03 is 17 mm. From 04 upwards, multiply by 5: 04 is 20 mm, 05 is 25 mm, 06 is 30 mm.
- Read the letters after the number. Z is one metal shield and ZZ two metal shields. RS, 2RS or a similar code means rubber seals; makers differ on whether RS alone means one seal or two, so look at both sides of the old bearing. C3 means a little more internal clearance, used where the bearing runs hot or has a tight fit. N or NR means a groove for a snap ring on the outer ring.
- Match the letters, not only the number. A wheel needs sealed or shielded bearings with the seals where the old ones were. A gearbox or two-stroke crank bearing is often open, because engine oil or fuel mix lubricates it. If the old bearing had C3, buy C3.
- No number left? Measure the inner diameter (bore), the outer diameter and the width with the caliper. Measure in two places and take the larger figure. Give all three sizes and the seal type to the supplier.
- Look for other types: a tapered roller bearing (steering head, some wheels) has a separate cone and cup; a needle bearing has thin rollers. These have their own numbers and must be matched in the same way.
- Buy bearings in pairs for a wheel, and keep the old one until the new one is fitted and checked.
Check your work
- The new bearing has the same number, the same letters and the same three sizes as the old one.
- It slides onto the shaft or into the hub with the fit the manual describes, not loose.
If it did not fix the problem
- Fitting the new bearing: Replace wheel bearings or Check engine bearings for play and roughness.
- A tight fit in an aluminium case or hub: Fit parts using heat and cold.
- Outer race stuck in the hub: Remove a stuck wheel bearing outer race.
Reference: common bearing sizes (standard metric sizes, from the course bearing chart)
| Number | Bore | Outside | Width |
|---|---|---|---|
| 6201 | 12 mm | 32 mm | 10 mm |
| 6202 | 15 mm | 35 mm | 11 mm |
| 6203 | 17 mm | 40 mm | 12 mm |
| 6204 | 20 mm | 47 mm | 14 mm |
| 6301 | 12 mm | 37 mm | 12 mm |
| 6302 | 15 mm | 42 mm | 13 mm |
| 6303 | 17 mm | 47 mm | 14 mm |
| 6004 | 20 mm | 42 mm | 12 mm |
These are standard sizes, not values for one bike. Your bike's manual or parts list says which number it uses.