Fretting indicates repeated movement in a tight joint. Movement should not occur in the retaining area of the valve. Typically fretting is a result of the following items.
Loose valve lash
Engine over speed
Sticking valves in guides
Broken valve spring
Illustration 2 g01183438
Fractures will typically be brittle and/or fractures will be low cyclic fatigue due to an overloading in shock that is caused by excess velocities in seating of loose valve lash.Beach marks are clearly evident in the photo below indicating cyclic overloads.
Illustration 3 g01183441
Wear at the valve stems and/or valve bridges’ interface may also be present.
Illustration 4 g01183442
Wear on valve stem and/or bridge