This is an overview on how to remove the rear sprocket on a wr250r to change the gear ratio. I started with a 12 tooth front and 48 tooth rear which is a great ratio for off road. My bike is my commuter horse so I need a much more street able ratio. Thus this instructable. Also, it is NOT required to change both front and rear sprockets. I recommend replacing both gears and chain as a set
Step 1: Changing Rear Sprockets on WR250R
First step is to lift the bike using a buddy or brute force. Place a sturdy block or bucket under subframe. ( Or use a motorcycle lift if you wish).
Step 2: Changing Rear Sprockets on WR250R
Next remove axle nut and remove axle.
Step 3: Changing Rear Sprockets on WR250R
Now remove the adjuster blocks.
First you loosen the lock nut, which is a twelve millimeter on this particular bike. You loosen this up and the same thing on the other side. Then you'll get the actual adjustment screw or bolt, and if it's too loose then you need to go backwards with the bolt. If it's too tight, then you need to go forward with the bolt.
Remove the drive sprocket. Depending on your bike you may need to open the peened part of the nut to remove.
Install new sprocket on output shaft. Also it is a good idea to use thread lock.
Step 6: Changing Rear Sprockets on WR250R
Place a piece or cardboard or towel on floor, and rest tire on floor. Using a number twelve wrench and allen wrench,remove bolts on sprocket.
Step 7: Changing Rear Sprockets on WR250R
Depending on the size of your sprocket choice & length of chain, you might need to add a link to your chain. In this case I replaced the chain along with the sprockets. There are many references on the web that will direct you to the right combinations.
Step 8: Changing Rear Sprockets on WR250R
Before re-assembly, make sure to compress rear brake caliper pistons to allow the rotor to fit back in the caliper. Using an old brake pad or piece of flat metal, compress with a c clamp or channel lock pliers.
Step 9: Changing Rear Sprockets on WR250R
Once the new sprockets and chain are reinstalled, align rear wheel and reinstall axle.
Step 10: Changing Rear Sprockets on WR250R
Now it is time for chain adjustment. This is a very important step and you must use the revised procedure from Yamaha
Step 11: Changing Rear Sprockets on WR250R
At this step tighten up axle nut and check for tight spotss in your chain. If you don't have any, it is good. If you feel binding re-adjust. Once complete you are finished!