EDIT: Well, apparently there was already a tutorial about this. Oops. I looked for it and didn't find it. Sorry!
Repacking your wheel bearings is really not a big deal to do. This is one of the many things you should do when you first buy a moped that has been sitting, or has never had it done.
I followed the directions in the Vespa Haynes Manual to do mine. You could just read that, and you'd be fine, but I took more pictures than they did. You might read it in case I forget to tell you a step, though(page 62). Oh, and heads-up: I did this on a Vespa front wheel, so your assemblies may vary.
OK, first off, you've got to remove the brake plate. Make sure you keep track of every nut and washer, what order it comes off, etc, so you know how to put it back together. On the other side is the Speedo drive. Vespas should slide right off, but sometimes they're tight and you have to unscrew them.
Each side of the axle is held in place by two nuts. The first is just your average nut. Underneath is a special nut (called a cone) that is actually part of the bearing assembly. The two nuts are locked together. I found out that my pedal wrench was the right size, albeit too thick, for the cone. I ground it down a little, and it worked great. Now, here's the thing: only take off one nut and one cone! Leave the other side locked together. If you remove both, you have to recenter your axle. Not that it's a big deal, but I'm not going to do that in this tutorial.
OK, so keep in mind that when you remove the axle, some of the bearings on the underside might fall out. It is very important that you contain them. Also, according to the Haynes manual, mixing bearings is not allowed, nor is switching sides. Keep track of which side your bearings came out of, and keep each side separate. If some of your bearings fell out when you removed your axle, do that side first. Put your loose cone back in, and use that to hold the bearings in while you flip the wheel over. Set the wheel down so the cone is touching the table and those bearings will stay in place.
I use a magnet to pull the bearings out of the cup. It keeps me from dropping them. I also use a magnet bowl to put things in, as well as other little magnets I have around to just keep my pieces from rolling or flying away.
Throw your bearings into a cup with some degreaser. Yes, that is the retaining ring (see next step) already in the cup.
Next is removing the retaining ring. This thing is thin metal and just keeps grease in the cup. I use a flat screwdriver to gently pry it up. BUT, notice that I am NOT prying on the outside lip. I stick the screwdriver in to pry against the edge that is touching the bearing cup.
So, now you should have a view like this. Squirt some degreaser in there and let it sink in.
I use a plastic bicycle tire lever to scrape out the grease. Use plastic, not metal to scrape out the grease.
So once it's all clean, you're ready to start putting grease back in. I use either a flat screwdriver, or just a strip of Formica. Yeah, that stuff on your countertops? You can get free samples from Home Depot or Lowes, cut it into strips, and use it for just about anything. Anyway, I'm not shy with how much grease I put in, and the manual wasn't exactly precise, either.
OK, now make sure that your bearings are really clean, and stick them in the grease! MAKE SURE YOU PUT THE RIGHT BEARINGS IN THE RIGHT SIDE.
Did you clean your retaining ring yet? Do it! Then place it over the bearings. On Vespa, the right and left rings are different. I pushed mine in with my fingers. It's supposed to be flush.
Grease the cone on the axle and stick the axle back in place. Then flip your wheel over. HOLD ON TO THE AXLE!!!
OK, now repeat the process!
OK, now grease your loose cone and get it back on there.
Put your nut back on the axle and lock it in to the cone again. Oh, and remember from reading the manual that you're not supposed to tighten it down too tight. Get it down close and leave a tiny bit of play. You can go by feel and it will be ok. The wheel should spin freely and not feel tight at all. I find that it takes a little fiddling to get it just right because the axle turns a little as I tighten. Sometimes I have to fiddle with the brake plate, too, as it can get bound up when tightening everything. Just keep adjusting until everything is secure but the wheel doesn't feel bound up.
Good luck! Ike Pipe