This valve is one of the exhaust valves of the engine. This would involve removing one (or both) cylinder heads and replacing the damaged valve as well as any additonal parts that were affected, which could include the cylinder head itself.
Best case would be that the repair would involve getting the cylinder head machined and serviced at a specialty shop, and the faulty valve replaced, and the head reinstalled with a new head gasket......but worst case would be that additonal damage was discovered that would warrant the replacement of the cylinder head, or worse a damaged piston with a hole in it which would warrant rebuilding the bottom-end of the engine.
rick
February 2008