20367 Mariner SCREW, PLATE TO CARBURETOR (7/16")

Introduction
This Reuse and Salvage Guideline contains the necessary information in order to allow a dealer to establish a parts reusability program. Reuse and salvage information enables Caterpillar Dealers and customers to benefit from cost reductions. Every effort has been made in order to provide the most current information that is known to Caterpillar. Continuing improvement and advancement of product design might have caused changes to your product which are not included in this publication. This Reuse and Salvage Guideline must be used with the latest technical information that is available from Caterpillar.For additional information about this guideline, consult Repair Process Engineering of the Marketing & Product Support Division at 1 (309) 675-5434.Summary
These instructions give failure modes of valves for engines using the basic principles of wear and fracture to determine the most probable root cause of failure. This guide should be used with the additional documents in the reference section to define the reusability of valves. References
ReferenceSee Guideline for Reusable Parts and Salvage Operations, SEBF8002-05, "Valves, Valve Springs, Valve Rotators and Locks".ReferenceSee Guideline for Applied Failure Analysis, SEBV0554, "Principles of Wear".ReferenceSee Guideline for Applied Failure Analysis, SEBV0552, "Principles of Fracture".ReferenceSee Guideline for Applied Failure Analysis, SEBV0551, "Engine Valves".Nomenclature for Valves
Illustration 1 g01184370
(1) Groove for Retaining Valve Spring (2) Stem (3) Fillet (4) Head (5) FaceNote: The valve seat is the sealing surface between the valve face and the seat in the cylinder head.Tools and Equipment
Table 1
Required Tools    
Part Number     Part Description    
9U-7231     Flashlight    
8S-2257     Eye Loupe    
1U-7262     Magnet    
    Digital ProScope Microscope
optional    
    Straight Edge    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
FrettingFractures 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 MarksWear at the valve stems and/or valve bridges' interface may also be present.
Illustration 4 g01183442
Wear on valve stem and/or bridgeTight Lash
Valves may not display oil degradation, adhesive wear, or fretting if valve lash was too tight. Also if valve lash was too tight valve heads may show repeated contact with the piston. Tight lash may affect only one valve in a cylinder or all the valves within the engine.
Illustration 5 g01183449
Piston contact on valveIf the valve lash is too tight, compression and combustion gases may leak past the valve face and the valve seat. This will cause the visual signs of gas to be left behind on the valves' face and valves' fillet. The gas leaks may overheat the valve head and the valve stem which will cause the material of the valve to weaken.Carbon buildup or thick oxide coatings on the valve face or the sealing area of the seat can crack causing gases to leak past the valve face. When the coating cracks, the hot gases have a path to escape.
Illustration 6 g01183459
Traces of gasPiston Contact
Multiple cylinders displayed outlines of the piston crown and the piston crater on the valve heads. This intermittent contact indicated a valve to a piston contact. This contact can be seen in the following picture. Look at the valve stems for the following items.
Oil coking problem on sticky valves
Adhesive wear
Bent valve stem or stems
ECM for logged conditions over speed
Illustration 7 g01183476
Piston contacts on valves