I came across this detailed little write up about how to change the oil on the Yamaha motor in a snow mobile forum and thought I would share it here. Maybe someone might find it useful. I did not write this up just passing it along. 

1.) Drain the Oil Resivor.
2.) Drain the Crank Case (There is socket head cap on the bottom of the motor. You'll have to remove belly pan, and flimsy gaurd covering the bottom of the engine.
3.) Remove and replace the oil filter.The first time it's tight!
4.) Carefully remove the gold color elbow fitting from the bottom of the oil can. There's a screen that should be cleaned. I would do this after break in and then at least once every two years. I do it every time. Carefull not to loose the rubber O-ring in your drain pan. Clean/Reinstall
5.) Clean everything up, install new oil filter (remember to put oil on the O-ring before installing. You can precharge the filter if you like. Up to you.
6.) Replace drain bolts in both engine and oil can. Pour required amount into oil can. At least 3 quarts.
7.) You can pour the recomended amount in the top of the motor, some do, some don't. Again your choice.
8.) Start the sled, make sure you feel the oil can getting warm. Once the oil is warm, check the level, start it up again, wait, check the level. I repeat this until I have reached the desired level, and there is no change for two cycles. FYI, slightly below is better than slightly above.

Also check the oil with a warm motor and don't screw in the dipstick when checking the level.