The story began with BB-4600 which seems to be fine for 6 months, and then suddenly, at one evening after ride I realised that whole drivetrain is not spinning freely as it should. Quick inspection revealed that component which apparently should be quite robust died quietly. Left bearing in bottom bracked spins but with grinding feeling. After quick calculations was obvious that I need another one in order to keep my wheels rolling. Eventually decided to make a small experiment. I decided to replace bearings in old cups, and slightly upgrade them in the same time.
Step 1: Find Decent Bearing!
Step 2: Dissassemble
The cups are tricky to disassemble (actually stays "DO NOT DISASSEMBLE" on the cups). Shimano made the same size of hole inside cups as the internal diameter of bearings. So basically is a small gap (about 1mm) where you can actually attach bearing puller and disassemble it. Sounds almost impossible with standard bearing puller, so I came across with diy bearing puller made from cut washers, screw and other bits and pieces. Two washers on a screw and in between is another washer cut in a half. A sort of sandwich. The images shows only one piece slid.
So I've put the sandwich on the screw and inside move them aside so they catch the bearing and added a nut on top to keep everything compact. I must admit this is quite tricky to set it up, but once is done all you need is a vice or piece of tube as a spacer (or whatever suitable) and you can slowly pull bearing out turning the top nut.
After wrestling with diy puller for nearly an hour I had both disassembled. Pressing new bearings back was quickest and easiest part. I've put the bearings to freezer (old trick in order to use less force pressing them), and in the meantime cleaned cups, grease surfaces where new one will slide.
Step 3: Asemble
Step 4: Final Touch - Seal
Made covers from 5.25 inch diskette (do you remember them?! ;-) ) you can see on the pictures. They're probably no necessary but I've decided to have additional protection at least against sand.
The final product you can see on the last image, and I assume if you attempting to do it there's no need explain how to screw them again to the frame ;-)