1999 Volvo Penta "WT" Models Workshop Manual, Page 69Get this manual
Repair Valve Grinding
[] Pitted valves must be refaced to the proper angleValve
stems that show excessive wear, or valves that are warped
excessively must be replacedWhen an excessively warped valve head is refaced, sharp or thin valve margin may result because of the amount of metal that must be removedUndersize valve margins lead to breakage, burning, or preignition due to heat localizing on this edgeRefer to Engine Specifications in the