Are you sure its the valves? Is it a ticking sound?
I ask because there are two common problems that happen with the Ford Triton engine's:
- They tend to shoot out the spark plugs. Although the newer ones don't do this nearly as much (if at all) compared to the early ones, and
- The exhaust manifold bolts tend to break (usually after many miles though). My F-350 had two go and when the engine was cold you could hear the leak like a tick noise