2008 Polaris ATV Sportsman 300 400 H.O. Service Manual, Page 67Get this manual
ENGINE (300) If the contact area of the cutter is in the same place, the valve guide is distorted from improper installation and must be replacedBe sure the cylinder head is at the proper temperature and replace the guide If the contact area of the initial cut is greater than 75, continue to cut the seat until all pits are removed and new seat surface is evidentNOTE: Remove only the amount of material necessary to repair the seat surface5To check the contact area of the seat on the valve face, apply thin coating of Prussian BlueTM paste to the valve seatIf using an interference angle (46o)apply black marker to the entire valve face (A) If the seat is too narrow, widen using the 45o cutter and re-check contact point on the valve face and seat width after each cutBottom 60o or 75o Seat45o or 46o Top30o
NOTE: When using an interference angle, the seat contact point on the valve will be very narrow, and is normal conditionLook for an even and continuous contact point on the black marker, all the way around the valve face