These BORG rim brake hubs are simple to service. Take apart for the following reasons

1) to replace bearing

2) to replace freehub body 

3) to add grease to freehub mechanism.

Bearing require changing when they are not longer smooth. When the bearings spin with noise they are worn. They will spin freely at this point but there will extra drag with rider load on the wheel. Bearing life should be long. 

Insert 2x 5mm allen keys into end caps. Normal right hand thread and undo. One end cap will undo.

Insert a 10mm allen key into the axle and with the other 5mm allen key remove the other end cap.

The freehub bearings should be removed with a blind or collet style puller and refitted. 

Freehub pawls and springs are a spare part and can be replaced.

To remove axle knock it out with a rubber mallet from the drive side. The nds bearing will push out of the shell.

 Use a bearing puller to remove drive side shell bearing and a bearing press to fit new NTN 6902 bearings. 

The freehub bearings are NTN 6802. 

Pictured here are shell bearing with contacting seals and a freehub with non contacting seals.

The hubs are made with the tight tollerances that NTN bearings provide. Therefore use of other brands of bearings while possible may affect bearing life and hub performance. 

The question gets asked alot as to why my road wheels are not wider than 19mm well it quite simple -ETRTO.

ETRTO is a standard organisation that lays down specification for tyres and rims. Standards for bead hook design are mandated and for tyres. My rims conform and all the major tyre manufacturers conform to these standards too.

Wider rims are often hookless as well. Hooked rims are recommended for all road and gravel width tyres. Often the rims used for road and gravel are the same and non of the major tyre manufacturers say its fine to use there road tyres with hookless rims. Some say explicitly you should not. Hookless rim are really an mtb creation for tyres inflated to 30 psi or under. While some claim pressures are fine much higher for road tyres remember to hookless carbon rim (its mostly carbon) exists solely because some rim manufacturers find it too expensive to make there bead hooks properly. Some never made them properly in the first place (ENVE bead hooks don't conform to ETRTO standards). I don't offer hookless rims. If your using one no IRC road tyre should be used with them. The gravel tyres I sell should be fine used tubeless and with pressures under 40 psi. 

There are many rim and wheel manufacturers now touting 23mm, 24mm and 25mm internal width rims and some say tyres from 25mm wide are fine. They do this because wider is better innit and it more aero. 

The problem is tyre manufacturers say different. At the extremes when say mounting narrower 25mm or 28mm tyre to a 23mm internal width rim one risk is tyre blow off. This is risk is higher with hookless rims than hooked rims. However this is the extreme for example the 28mm tyre pictured below mounted to 23mm internal width rim/28mm external width. This may not actually blow off but it shows another problem. Tyre shape.

Tyre manufacturers like IRC want there tyres to have a shape range. The top of the tyre should form a circular arc so when riding your on the centre of the tread and when corning you move progressively over the shoulders the more you lean into the bend. 

With a stretched tyre the shape is flattened at the top and this does affect how the tyre handles. You maybe more aero but slower in the bends. This especially true off road with off camber and undulating terrain. 

The side walls are also more exposed with stretched tyres to damage. Gravel and potholes on the road or all those roots, stones and holes off road are more likely to slice a side wall. Nothing slower that a blowout tyre. Tubeless tyre pinch flats are also more likely with over stretched tyres.

This is why i am not following the wider is better trend. It works to a point.

Suggested tyres rims for rim sections. These stretch the older ETRTO guidance a but new guidance was issued in 2020 which confirms my chart. You can actually go wider than i suggest safely but higher pressures would be needed to avoid tyre squirm in bends. This also affects tyre performance so the max width seem to be practical  maximiums. The minimum width really are minimums and with some tyres there may be pinch flat issues. With the wider rims the min tyre width is barely recommended as these are off road tyres and pinch flats are more likely at the bottom end of the tyre range.

Rim  internal width mm       tyre width mm

15mm                                     23mm to 32mm

17mm                                     23mm to 36mm

19mm                                     25mm to 42mm 

20mm                                     28mm to 45mm

21mm                                     32mm to 50mm 

23mm                                     36mm to 60mm

25mm                                      40mm to 65mm

Most of my wheels have aluminum alloy freehubs bodies. Some people worry about cassette sprocket notchng. This concern is misplaced. Notching occurs for very specific and avoidable reasons. 

First riders are not strong enough to cause notching. Regardless of how strong you think you are you can't notch a freehub that has a properly installed lockring.

The pic is of one of my freehub. Notching should not get any worse than this. Its barely notched.

First notching can only occur if the cassette lockring does not provide enough preload to the cassette. Thay preload stops the sprocket slipping and notching the freehub.

Grease freehub splines lubricates them. Dont do it. It is likely to make notching more of a problem. 

Recommended lockring torque is 40 to 50 Nm.

Not all torque wrenches tell the truth. A good mechanic has feel. The tool and feel tell you if your getting tight enough. 

Due to manufacturing tollerances there  an be a range of preload applied to the cassette hence feel is important. So the correct torque  can be aplllied but the correct preload not. Don't be a torque wrench slave. Lubricating lockring threads does reduce the variation in preload applied but also increases it and could result in stripped threads. There we fit lockrings without greasing them. We ensure the threads are sharp and clean.This way the correct preload is applied to cassette when the lockring is at 40 Nm. 

Most lockring tigheneing effort is used to over come friction so dirty or damaged threads mean notching is more likely.

If you get a freehub that notches, file the burrs and thick about what could have caused it. Its not the freehubs fault you just need to be a better mechanic.

One of my alloy freehubs is pictured after a few thousand km. No notching because i avoid the errors above.