Today I pressed the bearings into the hub, using a M5 bolt, nuts and washers, and 8mm din 433 narrow washers that can fit inside the 15.875mm hole. The R4 bearings with 6.35mm bore is a huge pain to work with because metric fasteners have to be undersized, which are weaker and leaves gaps and creates the risk of tilt. One of the bearings didn't go in flat, and was tilted at a 5 degree angle but there was nothing I could do since I already got in halfway, except to complete the process. It was making really bad scratching sounds as the tilted bearing moved inward.
Towards the end, I forgot that I had planned to wrap the bolt on each end with a thin strip of masking tape to increase the section of the bolt from the bearing and a little bit into the spindle, increased to 6.35mm to serve as a kind of sleeve to fill in the gap, which would have reduced the risk of a tilted bearing. But it was already too late by the time I remembered. I did eventually add the tape sleeve for the last few turns of the bolt, and the bearing eventually flattened out and seated against the inner lip of the hub. But I don't know if I had caused any damage to the bearing that was tilted or the bore hole on that side of the hub. Spinning the wheel produces a feeling of a little bit of roughness in the bearings, but it still spins for several revolutions without stopping, so maybe it's ok. But the bit of roughness could be a symptom of some pitting in the trace from the tilted installation, which might quickly become worse. Well, there is nothing else I can do about it now. Those were the last 2 units of the Enduro R4 bearings that I could find commercially available at online stores in the entire country.
I noticed after pressing the new bearings (and before removing the old one) that one side of the hub has the bearing 0.4mm more inwards than the bearing on the other side. I'm not sure why it's like this, but the inner race tracks on both sides are already contacting the inner spindle, so they can't be pressed any further.
For my next front hub, I would avoid the Dahon Kinetix hubs that use the R4 bearing, and find one that uses the older design with the 688 bearing with larger inner diameter of 8mm. There are cheap pullers and presses available for 8mm bore holes. Handsonbike blog has a photo of the 688 bearing in the Novatec A551SB hub. So I assume that the A211SB and A215SB hubs probably also uses 688 bearings. Otherwise, I would instead go with loose ball bearing hubs which are easier to service yourself without special tools or requiring you to build special jigs. But there aren't many loose ball bearing 74mm hubs. The only one I could find readily available are Tern branded, but most of them are solid axle with nuts instead of quick release skewer. The loose ball bearing hubs have low chance of you damaging it when servicing, and has better lateral stability. And if the cones become pitted, you could simply buy a the really cheap hub again for $20 and swap the cones and balls, whereas a version with cartridge bearings requires you to go through the trouble of extracting them and pressing new ones in. The only issue with loose ball bearing hubs is your ability to feel how much is good preload to apply when tightening the lock nuts.
