Originally Posted by
gfk_velo
Couple of notes re P!N20's post, for the avoidance of confusion:
To say that they don't do much work is to misunderstand the construction of the hub - they resist considerable loadings from pedalling as the angle of the chain to the cassette means that there is a constant rotational load in the axial plane of the hub which is bourne solely by these bearings. Over-use or indistriminate use of penetrative degreasers and thin (especially aerosol) oils in and around that area of the bike can also lead to the grease being leached out of these bearings, allowing corrosion to occur, so replacement is a job which mechanics do undertake from time to time.
Agreed, totally. I replaced sealed bearings using simple sockets and tools with set of Japanese Nachi 6001-2rs bearings, and they're a perfect fit. Good idea to carefully measure all the dimension of the old bearings. In my case, 12(ID)x28(OD)x8(W) in mm. The hardest part is unseating the old bearing at the back and then reseating the new one with the locking installed. The old bearings were TOAST on mine. You will need to remove all but the outer most drive-side seal from sealed bearings to get the free spinning action you need, at least I had to. Interested in others' thoughts. It was not easy, but glad to have the new parts.