This how-to is for an aggressive chassis Polaris (98 XCR 700). Most are close to the same, major differences in sleds with mechanical reverse.
1. First, drain your chaincase oil. There's a drain plug on the bottom, accessible outside the belly pan on the bottom. If yours doesn't have one just use a syphon through the dipstick hole and get as much as you can out.
2. If you have liquid cooled brakes, you're going to need to drain about half of your coolant out as well.
3. Loosen your track tension. Makes getting the actual chaincase off much easier.
Next, remove the pipe or pipes:
I prefer vise grips, they keep the springs from flying all over:
I already did, but remove the 4 screws that hold the chaincase cover on. This is what the inside looks like:
Inside you have a top gear, lower gear, chain, and tensioner (seen at right). Now you want to loosen the jam nut on the tensioner. It's a 1/2inch.
Then loosen the actual bolt. It may just be finger tight or might require a socket. After you loosen it all the way your tensioner is just kind of flopping there and you can remove it.
Now you need to remove the gears. The top is held in place with a castelated but and a cotter pin. I bend the cotter pin with a flat-bladed screwdriver until I can grab it with channel locks or pliars:
Then you can remove the bottom bolt and washer. 1/2inch I believe:
Then it's just a matter of pulling the gears off. Since the chain won't let you wiggle them you need to pull them both off at the same time.
Now it's time to get to the brakes so you can get the caliper off. I had to remove the little toolbox thing. Mine was held on by about 400 Torx screws.
Remove the clamps that hold the brake cooling lines on (if applicable).
This bracket is held on by the same bolts that hold the caliper in:
Now it's just a matter of prying the caliper off the rotor and twisting it out of the way.
Now it should look something like this:
Start getting the actual chaincase bolts off. They are all carriage bolts and are accessible with your hand in the tunnel. There are 4 total.
After you have all 4 off, it's a LOT of wiggling, prying, moving, knuckle-busting to get it off. Eventually you will be looking at this:
Congratulations. Your chaincase is out of your sled. Now it's time to do what we dissasembled it for.
This is a very blurry picture of the snap-ring that holds the bearing in.
Use snap-pliers to get it off. No, don't use a pair of needlenose you've ground the tips of. At least get cheapo tools from Harbor Freight!
After you have the snapring out, flip it over. I use a crappy "made in tawain" socket to pound the old bearings out. You want it bigger than the OD of the bearing but smaller than the seal.
Flip the chaincase over, and use either a bigger socket or a punch to get the seal out.
Tap the new bearing in, same for the new seal. Repeat for other side (bottom or top depending on which one you started with).
Make sure the place where the seal rides is clean and not "buggered" up. If it is it will chew up the new seal really quick.
Reassembly is the reverse of dissasembly. Clean and inspect the chain/gears/splines when reinstalling. I use threadlock on the nut/bolt that holds the gears on. Take the cover seal off and clean it. Also use a dab of RTV on the top where the ends meet to help seal it. Clean the dipstick as well before reinserting. CLEAN THE BRAKE ROTOR with brake cleaner!