3116 and 3126 Truck Engines Failures Fretting

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

Fretting

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

Beach Marks

Wear at the valve stems and/or valve bridges’ interface may also be present.


Illustration 4 g01183442

Wear on valve stem and/or bridge

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