When I do the following when I service cup/cone bearings:
- Remove axle and balls from the hub,
- Thoroughly clean all components, including the space between the cups in the hub,
- Inspect both the cup and cone bearing races for any damage. Cups are pretty durable and they normally last ok but cones will be the ones to show any damage and is pretty obvious when you look at them. Any holes or chips in the "shiny" section when the bearings rolls is damage and the cones should be replaced. Damage in the cups is different as cups are generally not replaceable and generally requires the hub to be replaced. At this stage, you might as well get a new wheel,
- If all components are serviceable, I will install some grease into the hub into the cups and install all of the balls. The grease holds the ball in nicely but you still need to be gentle not to bump them out,
- I then install the axle. Ensure the cone and locking nut that are still on the axle are pretty tight and install into the hub with the other cone tightening up until finger tight, when finger tight, install the locking nut and lightly do up,
- I then tighten the locking nut up or undo the cone that I just put in. I try and find the balance between the graunchy feeling and loose bearings. If the bearings feel tight and graunchy and the locking nut hasn't been fully tightened, using cone spanners, I will hold the cone and locking nut (both on the re-installed side) and loosen the cone ensuring the axle doesn't turn, if the bearings go loose, tighten the bearings using the locking nuts. Keep on going backward and forwards like this until the locking nuts are tight (and I mean tight) and the wheel spins freely without and graunchyness or looseness,
- If when you reinstall the wheel, the qr binds the bearings then you haven't tightened the locking nuts sufficiently. Remove the wheel and continue the above until the locknuts are tight and the qr don't bind the bearings.
Last word of advice though. IMO, cup/cones bearing systems are not suited for offroad applications. Yes, you can might be able to make them spin better than sealed bearings and their "easily" serviceable but you need to service them regularly and it doesn't take much to screw a cup/cone hub and mtbing generally is no where near as "clean" as road or track riding. I learnt this lesson the hard way and screwed a rear XT hub in the first outing. Generally you will get at least 12 months out of a set of bearings in a sealed hub without touching them and then your up for about $20-$50 (depending on the bearing) to replace them. I also know of guys that have got 4+ years out of sealed bearing and they are racing most weekends and the wheels still spin nicely.