Valve Seats

WARNING: This page is about a different car, the 2002 Nissan Pathfinder. However, it is still accessible from the selected car via links, so may be relevant.

Check valve seats for any evidence of pitting at valve contact surface, and reseat or replace if it has worn out excessively.

Before repairing valve seats, check valve and valve guide for wear. If they have worn, replace them. Then correct valve seat.
Use both hands to cut uniformly.

Fig 1: Using Both Hands To Cut Uniformly
Courtesy of NISSAN MOTOR CO., U.S.A.