Wheel bearing replacement is a common job on ATVs. This machine is a Yamaha Grizzly, but most machines are put together the same way.
Once you remove the wheel the first step is to remove the large nut that holds the hub on the axle. On Yamaha machines the nut is locked in place by a small portion bent into a groove on the shaft. I use an old screwdriver that I have ground down to match the groove to pry this spot out.
The easiest way to remove this nut is with an impact wrench. If you do not have an impact wrench you need to find some way to keep the hub from turning. One way to do this is to put a pry bar between the wheel studs. Be sure to protect the threads on the studs with a short piece of rubber hose if you are going to pry on them.
Once the hub is off the spindle must be removed from the vehicle. The ball joints (red arrows) and the steering tie rod (green arrow) need to be disconnected. These are held in place with a nut on the end of a tapered shaft.
Remove the nut and pry or pound the ball joint loose. If you are going to pound on the threaded end use something soft like a lead hammer to avoid wrecking the threads. The other tool pictured is a ball joint fork, it is simple pounded in between the parts and the wedge shape drives them apart.
When you have the spindle on the workbench remove the clip that holds the bearing in place. This one has holes in the ends that make it easier to get out.
If you look close at these clips you will note that one side has sharp edges and the other side has edges that are rounded over. (The top clip is sharp side up, bottom clip is round side up, it is more obvious in person than it is in the photo.) These edges are a result of the way that the clips are stamped out when they are made. When installing clips like this you should always put the sharp edge facing the direction that the clip is being pushed towards. The sharp edge makes it less likely to slip. In the case of these wheel bearings the sharp edge goes up.
To remove the old the old bearing I use a large hammer and a piece of pipe to pound the bearing out from the back side. I do quite a few of these wheel bearings so I have made up a jig to hold the hub when I pound on it. Make sure you have something solid to pound on. I have an old cast iron weight from a tractor (about 75 lbs) that I put on my workbench. In my old shop in Minnesota I had a large anvil to pound on. If you don't have an anvil you may want to put your work on the floor.
Before you in install the new bearing you must make sure that the inside of the hub is clean. Make sure there is no crud at the bottom of the bore or in the groove around the top. Scrape or wire brush it out.
Heating the hub will cause it to expand and allow the bearing to go in much easier. I use an electric heat gun, but a torch will also work.
When installing the new bearing you can only push or pound on the outer race (green arrow). If you apply any force (especially pounding) to the inner race or seal (red arrow) you will damage the bearing. If you heated the hub up enough the bearing will drop in with only a few minor taps.
On this job I used a hammer to pound out the old bearing and tap in the new one. It may seem a little crude, but with care it works fine. A hydraulic press could also be use to remove and install the bearings. It would give a little more control, but the rules about protecting the inner race still hold true. You must only push on the outer race. An old bearing that has had the outside diameter ground down slightly makes a good tool for this job. It can be used to press the new bearing in place and insure that the force is applied evenly.
Once the new bearing is seated all the way into the bore, install the clip to hold it in place. Now the hub is ready to go back on the vehicle.