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Front [sealed bearings] , go in from the frint and push it against the first clip. Next part is seal, push in from the inside against the clip, flat part of the seal to the clip..There should be a shoulder or another clip to keep the inner bearing from moving forward and letting the crank web hit the case.  No reason for the seal if good sealed bearings are used on the crank..NSK brand with brown rubber seals....Beware of Chinese sealed bearings with black rubber seals, they can't hold the case pressure necessary

To help with this complexity, the Boca Bearings website allows you to select a wheel brand and exact model in order to get the right sized bearings. For each bearing size you will find the different types of bearings available: chrome, steel, hybrid ceramic, and complete ceramic. For fag bearing selection, the important dimensions are the inside diameter, outside diameter and the width, so vernier calipers are particularly useful in measuring your current bearings first.

For the Mavic Ksyrium road wheels we were initially going to use in this review, we had the bearing dimensions but couldn’t match the model nor find all of the bearing sizes on the Boca site. We then tried to find bearings for some Bontrager mountain bike wheels and, though these wheels were not listed, we found matches for four of the five bearings, so we ordered them.

After a lot of planning it was time to get our hands dirty. We pick up the action with the old koyo bearings already removed. Before considering getting the new bearings in, the hubs first need to be prepared, particularly if the wheels have already seen a bit of action. A good clean with a rag will get any grit out and a blade can be used to remove any burrs inside the hub and at the hub ends, so that metal shavings aren’t pressed inside when the bearings are fitted. After a coating of light oil (as opposed to grease) the hub is ready. The key to pressing in the bearings is to press them in perfectly straight, so don’t even think about using a hammer.

Removing the old bearings and fitting the new ones requires specialist tools and, since all hubs are different, there is no single tool that will do it all. Aaron Dunford is mechanically adept and he had built some of the tools we needed for this job. Some tools were as simple as nuts and washers on a quick release skewer combined with the old bearings to safely press the new ones in; the quick release is used to slowly leverage them into place. 

seal ring 120x150x12-rubber/stteel 

housing SN 218 FR 

NEEDLE ROLLER BEARING HK2016 DIN 618-1/ISO 3245