Properly maintaining your motorbike not only keeps it safe, it also means it handles and performs at its best. Doing some - or even all - of the work yourself can save you money and give you more satisfaction with your bike.
If the seals around your bike's axle are in good condition, the bearings should be fairly well protected. Keep your wheels clean, but don't get too close to them with a pressure washer, as that will blow the grease out of the bearings.
Wheel bearings on motorbikes can last 100,000 miles or more if well maintained, but blowing grease out or riding in deep water will shorten their life, as will severe impacts from off-road riding, wheelies, etc.
Bearings with sealed surfaces should not require maintenance, but bearings of the open cage design will wear out after a few years of use if they are not properly maintained.
The technique required to replace the front and rear wheels of a motorbike is generally the same, with the rear wheel usually being slightly more involved and carrying more bearings.
Step 1: Remove the wheel
Once you have the wheel out (remember, it's always much easier if you take the calipers out first), place the wheel on the two pieces of wood supporting the rim, but leave the brake disc off the ground - this will protect the rim and disc when you start hammering away.
Step 2: Remove the dust seal and snap ring
At the rear, there may only be a dust seal on the other side of the sprocket carrier, but remove any dust seal covering the bearing; you can remove it with a flat-bladed screwdriver.
After the seal has been removed, wipe off any grease and double check for snap rings; using snap ring pliers, carefully remove it and place it in a safe place as you will need it again.
Step 3: Float the first bearing out
With a powerful blow, start driving the bearing out, first one side, then the other, then 90 degrees, then the other, and so on until the bearing falls out of the wheel, most likely followed immediately by the spacer.
Step 4: Move the other bearing out
Now turn the wheel over, making sure it is secure on the long piece of wood, and repeat the process on the other bearing.
Once they are both out, check the wheel for any damage and also give the bearing housing a good clean - use a screwdriver or pick to get any dirt out and make sure you clean the grooves in the snap ring too.
Step 5: Fit the first new bearing
Before fitting the new bearing, find a sleeve that is big enough to just press against the outer edge of the bearing, but still fit just inside the wheel (remember, the outer ring may be a different size). If you don't have a suitable sleeve, you can grind off the outer edges of the old bearings so they can go in and out of the wheel.
If the bearing you are fitting does not have a dust seal covering the ball, grease both sides.
Step 6: Fit the new seals
On the front wheel you may have a seal to fit on both sides; apply grease to the back (open side) of the seal and wipe around it, or if the new bearing is an open design, apply more grease if you can.
Step 7: Replace the bearings
That's it. Now it's just a matter of reinstalling the wheel and checking that everything is fully secured and safe before riding. Make sure there is no grease or oil stains on the brake discs or pads and double-check your work.