Originally posted by Yellow YZ400: How often should you change the oil in a yz400. How often should you change the rings in a yz400. I changed the oil and air filter every 3 hours (I do hare scrambles that are that long, so I kind of made that my interval). My 99 ran strong for over two years on this schedule, and I still was not considering changing the rings. I just sold it and it ran great.