Failure Analysis on Diesel-Engine Valve Springs

A diesel engine used in a truck had a trouble when servicing. Inspection indicated that four exhaust and intake valve springs and two exhaust and intake valves were fractured. Fractographic studies indicated that fatigue fracture is the main failure mechanism for all of the four valve springs. Under the action of the maximum normal stress, the fatigue crack initiated in the spring wire of coil 1.3-1.5 from the upper end of the spring. This region is also the most damaged location by contact friction wear. The fracture of the intake and exhaust valve stems also suggests fatigue failure probably as a result of the failure of the associated valve springs.