SB20 - Flywheel Axle and Cog Bearing Service

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Can You Service Sealed Bearings?

Sealed bearings, like those in the SB20 flywheel, can be serviced to extend their lifespan.  You can often reduce the rumbling sounds and vibrations that occur after several years of use. 



✅ Bearings with plastic dust seals are serviceable. You can remove the seal, add grease and then replace the seal in a few minutes. The Axle and Cog Bearings have plastic dust seals. This post shows you how to service them.

⚠️ The Flywheel Bearings have metal dust seals that are not easily removed. I offer partial servicing and replacement options in SB20 - Advanced Flywheel Servicing. 

  

What about Clicking Sounds?

"Clicking sounds" are a common issue with the SB20 flywheel. This happens when the outer ring of a bearing moves side-to-side.

🔬 Stages issued a service bulletin to address the issue: Flywheel Bearing PTFE Application.  It tells you to spray lubricant into one bearing on each side of the flywheel. 

I must admit, I am not a fan of this method. Spraying light lubricant is a half-measure. PTFE spray can dilute the grease inside bearings. While it can temporarily reduce clicking noises, PTFE spray can negatively affect bearing durability.

Greasing and re-seating the Axle and Cog Bearings, as shown here, is often a better alternative.

Video

Here's the video that shows the procedure.



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Who Should Do this Service?

1. Anyone who wants to extend their flywheel life. Sealed bearings can last a lifetime without servicing - but they can also fail after a few years. One way to maximize lifespan is to add grease once or twice a decade.

2. If you have grinding, clicking and thudding sounds that indicate bearing failure. All SB20 flywheel bearings are inexpensive. The service procedure shown can also be used to replace bearings.

3. You read the Stages service bulletin on quieting clicking flywheel noises, and want to do a better job.

In short, servicing sealed bearings is optional. Most bearings never fail. Extreme temperatures, and exposure to humidity can be a negative factor. Just keep in mind: Spraying lubricants like WD-40 or PTFE into your bearings (like mentioned above), will shorten their lifespan. Repacking your bearings with grease is a good maintenance step especially after a few years when you start feeling minor vibrations or hearing a few rumblings. You must balance this with your mechanical skills and confidence. If you are comfortable doing the work described here, go for it! Otherwise, consider just waiting for a bearing to fail. The effort needed to replace a bearing is about the same as servicing one.


Difficulty Level

Servicing the Axle and Cog bearings, require moderate DIY skills. I rate the difficulty to be 7 out of 10.




For context: Belt tensioning and alignment is a 5 out of 10.  Servicing the flywheel bearings (the subject of future blog post) is a 9 out of 10.  

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Servicing Details

Here are the main flywheel components:



Bearing Service Steps

Servicing Axle and Cog Bearings requires the following steps:

  1. Remove plastic covers. 
  2. Remove drive belt, axle bolts and tensioners.
  3. Remove lower PCB and brake stay. 
  4. Slide out flywheel.
  5. Disassemble axle and cogs, add grease to bearings, re-assemble axle and cogs.
  6. Slide in flywheel.
  7. Replace tensioners, brake stay and lower PCB
  8. Replace belt. Check tension and alignment. Tighten bolts
  9. Replace plastic covers. 


Remove Plastic Covers




  • Start on the non-drive side.  Remove both flywheel covers. All use 3 mm hex bolts.
  • Move to the drive side. Remove the front and side covers. Once again, 3 mm hex bolts.
  • Side cover tip: Position cranks at 7 o'clock. Pull the cover down and to the left, to remove.
  • 🎬 See the video for more details.

Remove Belt and Flywheel Fasteners

  • ⚠️ Loosen the Vertical 6mm Bolt behind the non-drive Axle Bolt. 
  • Loosen both 14 mm non-drive Axle Bolts.
  • Remove Tensioners.
Note: The video shows loosening the non-drive-side axle bolt and followed by the non-drive-side tensioner. You might need to remove both axle bolts to allow enough fore-aft movement for the tensioners to be easily removed.


Remove Lower PCB


  • Remove connectors from Lower PCB.
  • Remove Lower PCB.
  • Remove Flywheel Brake Stay.

Building a Flywheel Support

The Flywheel is heavy. Stages suggests using a pair of 2 x 4 supports as shown:




I found this setup to be a bit unstable - especially if the flywheel starts to slide sideways.

An alternative approach

I used a small 2 x 6 support board with notches that fit over the hex bolts on the SB20's front feet. These bolts are spaced 6 inches apart. They help hold the support board in place, as you tilt it fore and aft.  



Flip the support board over. The notches on the board align the hex bolts to create a mini seesaw that tips to keep the Flywheel supported. 



Roll up a medium sized towel so it fits snuggly under the Flywheel. You can tilt the board backwards to get a better fit. Check from the front to ensure the towel is centred.

Slide Out Flywheel



With the support towel and board snuggly positioned, slide out the Flywheel. 


Remove Drive Cogs

Lay the Flywheel on a blanket.  Get ready to flip it over several times in the steps that follow. 






Summary:

The Drive Cog is removed by unscrewing the Flange and Lock Nuts followed by the Retainer Clip.

You can then push out the axle from the other side after removing the Cap Nut.










  • Remove Flange and Lock Nuts.
  • Remove Retainer Clip.
  • Lift Cog assembly to remove. 
⚠️ You may not have a enough clearance beneath Flange Nut to slide a flat 17 mm cone wrench onto the Lock Nut. 



In this case, you should hold the non-drive-side 19 mm Flange Nut with a wrench/socket while you unscrew the drive-side 19 mm Flange Nut.  My next blog post proposes a solution to this problem.


Service Drive Cog Bearings


  • Service outer Cog Bearing first. Lift dust seal with utility knife
  • Add NLGI 2 bearing grease.
  • Replace dust seal.
  • Repeat these steps on inner Cog Bearing.  

Remove Axle and Axle Bearings




Summary:

The Axle is removed by unscrewing the Flange Nuts followed by the Cap Nut.  

The Axle and Axle Bearing on this side can then be pushed out from the drive side.  

You can then use the Axle and Lock Nut to push out the drive side Axle Bearing.  










  • (non-drive-side) Insert Freewheel Tool (Park FR-1) and unscrew splined Cap Nut.
  • Tap drive-side Axle from to extract.
  • Use Axle and Lock Nut to push out drive-side Axle Bearing.


Service Axle Bearings


  • Lift dust seal on drive-side Axle Bearing with utility knife
  • Add NLGI 2 bearing grease.
  • Replace dust seal.
  • Repeat these steps on non-drive-side Axle Bearing (while still attached to axle).

  • Stages suggests adding Loctite to prevent clicking and squeaking. You should clean the outer ring of both bearings with isopropyl alcohol, apply Loctite adhesive and then wait 24 hours prior to use. 

Re-Assemble Flywheel



  • Replace drive-side Axle Bearing.
  • Insert Axle from non-drive side
  • Replace and tighten non-drive-side Flange and Lock Nuts
  • Replace and tighten Cap Nut
  • Replace Retainer Clip
  • Replace and tighten drive-side Flange and Lock Nuts
⚠️ You may not have a enough clearance beneath Flange Nut to slide a flat 17 mm cone wrench onto the drive-side Lock Nut. 



In this case, you should hold the non-drive-side 19 mm Flange Nut with a wrench/socket while you tighten the drive-side 19 mm Flange Nut.  

I writing a new blog post that proposes a solution to this problem.  Stay tuned.

Re-Install Flywheel



  • Reposition the towel + board support.
  • Slide in Flywheel.
  • Tighten 14 mm Axle Bolts.
  • Tighten the vertical 6mm bolt behind the non-drive Axle Bolt. 

Replace the Covers 


    • Non-drive-side: Replace both flywheel covers.
    • Drive-side: Replace drive-side main and front covers.  

    Cleaning Up

    Use isopropyl alcohol for cleanup. It will not affect bearings if you splash them.  Solvent properties disappear after the alcohol evaporates in a few minutes. 



    References

    Servicing the large Flywheel Bearings: SB20 - Advanced Flywheel Servicing. 

    Drive belt tensioning and alignment: Stages SB20 - Drive Belt Adjustments (2025) 

    The 6000 2RS bearings on the flywheel axle have plastic dust seals that are easily removed and replaced.  They are serviceable and can be greased. The same goes for thr 6807 2RS bearing in the flywheel cogs.  

    The 6910Z bearings in the rotating flywheel shell  have permanent metal dust seals that are not easily removed.  I will cover how to do partial servicing in an upcoming blog post.

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    Replacement Bearing Numbers

    Axle Bearings: 6000 2RS bearing

    Cog Bearings: 6807 2RS bearing

    Flywheel Bearings: 6910Z bearing


    Stages Service Documents

    Stages SB20 Service Bulletins 

    TSB-02202025 – SB20 Flywheel Repair Kit





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