ELBOW 7S7684 - Caterpillar

Illustration 10 g01183500
Valve TulipingHigh temperatures may also reduce the viscosity of the oil that allows metal to metal contact with the valve guide. Metal-to-metal contact can create adhesive wear.
Illustration 11 g01183506
Metal-to-metal wear (1) Bottom of Guides' Contact (2) Oil coking (3) Adhesive wearOil Quality
Varnished oil can accumulate on the valve stem near the bottom of the valve guides' contact. This accumulation of varnish is similar to the happenings of valves at high temperature. The buildup of varnish can cause the valve to stick in the guide. Valves that stick in the guides are likely to contact the pistons.The following items should be examined when a problem with the quality of oil is suspected.
Quality of oil
Oil change intervals
Application of Machine
Operating conditions
Illustration 12 g01183511
Effects of various qualities of oil (1) Corrosive Pitting (2) Bottom of Guides' ContactThe magnified view shows the surface of the valve stem to be pitted from corrosion. Pitting from corrosion is often confused as adhesive wear. Pitting that occurs in one valve stem usually will display the similar characteristics in all valves.
Illustration 13 g01183516
Surface pitting on valve stemAs the oil condition continues to degrade, consumption will usually increase leaving deposits on the valves' fillet and the valves' face. Corrosion may occur in any areas in contact with oil.
Illustration 14 g01183522
Deposits of oil on a valve (1) Build up of oil coking. (2) Corrosive pittingChordal fractures are the results of cyclic overloading. The chordal fractures usually begin in the area of the valves' fillet. The overloading is localized to one side of the valve head. The following items are causes for chordal fractures.
Valve, seat, and/or misalignment of guides
Bent valve
Foreign debris on valve face
High temperatures of combustion
Illustration 15 g01183525
Chordal fracturesIssues with Parts
Valves seldom fail due to problems with materials. Some failure modes that may occur are listed below.
Faulty inertia welds
Inclusions in the metal
TIR of seat to guide (misalignment of guide to port hole in the fire deck)
Illustration 16 g01183528
Fractured material When the inertia weld is excessively hot, the face of the fracture will have a twisted appearance. The valve stem at the inertia weld may be attracted by a magnet.
Illustration 17 g01183531
Twisted appearance on the face of the fractureIf the inertia weld is excessively cold, the face of fracture will have an appearance of a star and a magnet should not be attracted to the fractured head half of the valve.
Illustration 18 g01183533
Appearance of a star on the face of the fractureThe magnified picture of the face of fracture below started at an inclusion.
Illustration 19 g01183534
(1) InclusionGlossary
Fretting - Fretting causes a worn spot on metals by micro welding.Lash - Lash is the distance between the rocker and the valve.Adhesive wear - Adhesive wear is also known as an adhesive metal transfer.Beach marks - Beach marks are markings on the face of fracture that are associated with the propagation of cracks due to fatigue.ECM - Electronic Control ModulePlastic deformation - Plastic deformation is the permanent change in shape or size of an object without fracture. This is produced by a stress that is sustained beyond the elastic limit of