First let me say that bearings and water are not exactly a match made in heaven. Your skate bearings do not like water. If you get caught or skate in the rain, skate through a puddle, walk through the snow (yes, I've seen this) chances are that you will not be able to get home, disassemble your skates and soak the bearings before some damage has been done. If you're the one I've seen walking through the snow, you probably don't care anyway.
I'm amazed at how many times I resell bearings to people who have purchased them from me already (not that I don't want their business, and people do buy extra sets, and try different brands), but if you keep them dry, lubricated and clean, there's no reason why they shouldn't last for many, many years. I'm still using bearings that are at least 8 years old and I wouldn't trade them in for anything. If you take good care of them, they usually get better (faster) with age.
Here's the trick...Spin the wheels. Are they quiet? If not, this means that there is a foreign particle in the bearing. These particles if left in there will act as an abrasive and slowly grind away at the bearings. Remember, the clearances in these bearings are very tight, so it doesn't take much dirt to make noise. Higher abec rated bearings don't tolerate foreign particles as well as a looser, lower abec rated bearing will for this reason. The same holds true with lubricants (too heavy a lubricant in a tight bearing will slow it down). This is why I don't recommend a bearing tighter than an abec 3. Bearings that have high abec ratings are designed for very high RPM machinery, we're talking 150,000 RPM's and up. Your skate bearings don't come anywhere near this speed. The goal here is to use a quality precision made bearing that's not to tight as to restrict movement, yet tight enough to offer the needed amount of precision. This is why the Bones Swiss bearings are the most widely used bearing on the market. If you compare them to even an abec 3, you can see the difference. They are a very loose bearing.
Now getting to the maintenance. Remember, this is something anyone with a little common sense can do, it's not like working on the space shuttle or anything. Don't let to size of this article fool you. It's really very simple. I'm just going into detail and trying to cover all the bases. The first order of business is to remove the wheels. This is something that should be pretty simple to do. Your skates should come with the necessary tools. If not, generally you'll need a 5/32" Allen wrench, sometimes two. Once you remove the wheels, you have to remove the bearings.
Depending on the type of axle system being used will determine the procedure for removing the bearings. Most older, and cheaper rec. and fitness skates use a hollow spacer which extends to the outer edges of both bearings, when inserted in the wheel. Usually these spacers are plastic. The axle passes through the spacer. When removing these types of spacers, it would be a good idea to replace them with metal ones. The benefit is substantial. (The wheels will spin so much better!) To remove the bearings from the wheels, you will need to push on the spacer which will push one of the bearings out of the wheel. You can either use a tool which is made for this (there are many, and one may even come with your skates), you can use a 5/16" bolt, or if the bearing's not to tight in the wheel, you can use the edge of the Allen wrench. Once one bearing is removed, you can use the spacer to push out the other bearing. Some skates have a similar setup except the spacer is threaded. To remove these types, you can just use one of the axle bolts, thread it into the spacer a bit, and push.
Some fitness skates are now using an axle system which is like the type used on speed skates. These types use a floating spacer between the bearings, with a larger diameter axle aligning everything up. On this type, you can either position the spacer so it protrudes across the opening In the inner race (the part where the axle passes through) and use something to push on the spacer, or the preferred way of using a specially designed tool which is made to hook behind the inner race and then you can pull the bearing straight out.
There are several types of bearings being used. Some have factory installed shields which were not designed to be removed. On this type, I recommend using a small screwdriver to carefully pry up on one of the shields, against the inner race and pop the shield off. Do this to only one side. Be careful that you don't dig the screwdriver in to deep and contact the bearing retainer (the part that separates all the balls). This will enable you to clean out the bearing and when reinstalling it, you will be placing the open side towards the center of the wheel, sealing that side against dirt.
Some bearings come with one side already open, and have a non removable shield on the other side. Some have a removable one, on this type, I recommend removing that shield for better, easier cleaning. Other bearings come with removable shields on both sides. On these I recommend removing them both. Some bearings come with removable plastic bearing retainers. I don't recommend removing these. You can usually clean the bearings out just fine without removing them. If you do, just be careful that you don't damage them, both on the removal and also the installation as they are very delicate, especially on the new mini bearings. Also, if you do remove them, don't let all the balls accumulate together as the bearing will fall apart and you may loose some of the balls.
Now, there are mainly two different types of shields being used. One is a metal type which is held in by tiny snap rings. These are basically the same as the non removable ones, except they can be replaced again. These are also the highest maintenance type of bearings. There is always a gap between the inner race and the shield. This gap allows dirt to get into the bearing, especially if you wipe the bearings off while rotating your wheels. You will notice this problem more if you are using oil to lubricate your bearings and not grease. When using grease, the grease gets slung by centrifugal force to the furthest edges of the bearing race and shields and sticks there along with a lot of the dirt. With oiled bearings, the dirt just gets washed around in the bearing along with the oil. Anyway, to remove this type of shield, you'll need a pin. You need to find the edge of the snap ring and pry the snap ring over and up. Sometimes this is a real pain in the "A" because they just don't give you anything to hook into. On some though, they are made with a little protruding extension for doing this. I really recommend that when replacing these type of shields, leave one side off and place that side of the bearing towards the center of the wheels like I mentioned above. This will make servicing a lot easier in the future. In fact, if you want, you can usually get away with not removing the one remaining shield for cleaning.
Another type of shield, the easiest to remove and my personal favorite is the rubber type. these shields (seals) usually lightly contact the inner race and sometimes even slip under a ridge designed into the inner race. This contact is not enough to hurt skating performance, but boy what a difference it makes servicing intervals. You can usually even wipe the bearings off with a rag when rotating your wheels and not get any dirt into the bearings. They still manage to get hair into them, I've noticed though when using them indoors. These are very easy to remove, but are also very delicate. They bend easily since they have a very thin metal backing. The best way I found to remove them is either with a very thin pin, or my favorite way, a little "shoe horn" which you can make out of a thin piece of stiff wire. The thinner the better. Bend the wire in half, as to make a little loop. This will add stiffness, and not have any sharp edges to damage the seal (shield). Now insert the wire between the inner race and the seal and pry the seal up against the inner race. This will cause the outer edge of the seal to pop out of the outer race. You can now grab it (get under it) with your finger nail or something (the tool you made) and remove it the rest of the way. Installation is obviously a snap also.
Now it's time to clean your bearings. There are a lot of products on the market where you place the bearings in a jar with a solution, and do the "shake and bake" thing. Forget about this. All they do is get the dirt from one bearing to another. To clean the bearings right, you need to do them one at a time. Here is the best way I found. First you will need a cleaning solution. There are many citrus products out there which people like to use, what ever you use, just make sure it's not water based. I like to use a thin solvent like mineral spirits. What ever you do, DO NOT use gasoline! There is an additive in unleaded gasoline which has been known to cause leukemia in auto mechanics who use it to clean parts. Also, I once new someone who burned his house down because he was using it to clean motorcycle parts in his basement. Anyway, bad idea. Now, back to the cleaning. You will need a cup or container and a writing pen. Fill a cup or container with your cleaning solution. Now take a bearing (after doing what you have to with the shields) and stick it onto the pen (just jam the pen through the inner race so it holds the bearing). Now just spin and dunk the bearing in the solution. Using a quick jerking motion works the best. Do this until the bearing sounds quiet. If both shields are removed, you should turn the bearing over and continue. Once clean, Let the solution dry from the bearing. If you have access to compressed air, this is the best way to dry the bearings, and also it will surely remove any stubborn particles that may be giving you a hard time. Just blow the air straight into the bearing. Also giving the bearing a little spin with the air works well, just be careful, you don't want to spin the bearing to fast or to long, but a quick blast won't hurt the bearing at all.
Now that the bearings are clean, you need to lubricate them. There are many types of lubricants out there. Basically, if you use grease, the bearings will last longer before needing maintenance, but will be slower. If you use oil, the bearings will be faster, but will require earlier maintenance. A good compromise is a speed cream. What ever way you choose, don't overdo it. With grease, just a dab will do. With oil, one or two drops, depending on how big the drops are. Well that should do it, now you just need to reinstall the wheels and go skating. You will probably need to rotate the wheels at this time. You can read how to do this by clicking HERE.