LO 9-5 Identify and describe the purpose, construction, and operation of components used in the valve train

1.5. Valve Seat Inserts

Valve Seat Inserts

All premium diesel engines use replaceable valve seat inserts Figure 33. Typically, these are manufactured from material such as Stellite ® or Iconel ® . Replaceable inserts eliminate the need for complex machining processes to install a new valve seat into a damaged or rebuilt head. Their wear-resistant hardness and heat resistance add considerable durability and prolong an engine’s operating life. Valve seats have a minimum of three angles to ensure good gas flow and proper transfer of heat from the valve face. A narrow 45-degree seat promotes clean valve seats and good sealing. Three angle cuts on the seat provide improved gas flow and a narrow contact between the valve face and the seat to promote heat transfer Figure 34.

FIGURE 09-33: Replaceable valve guides and hardened valve seats are used on almost every heavy-duty diesel engine. They are pressed into the cylinder head.

FIGURE 09-34: Valve seat inserts are made from extremely durable materials to prolong engine life. Valve seats and guides are replaceable during the remanufacturing of cylinder head components.

Typically, valve face-to-seat contact width must be adjusted to within 0.0625–0.125" (1.5875–3.175 mm) for optimal heat transfer. Too wide a seat contact diminishes pressure per square unit of area and will result in less heat transfer from the face to the seat. This may seem counterintuitive, but high- pressure contact transfers heat better than low-pressure contact. To achieve this, a bottoming cutting tool opens the valve seat below the narrow face-to-seat contact line visible on the valve face. A topping cutting tool opens the valve seat above the 45-degree face-to-seat contact line.