Valve seat

The valve seat may be cut in the head or block metal ( if cast iron ) or head steel inserts may be pressed into the head or block , In aluminium heads
seat inserts are essential , though they are
also employed in some cast iron heads ,
especially for diesel and other heavy - duty
or highlyrated engines.

High-quality inserts are produced by compress
a metal powder in a ring shape mould to
produce what is called a Green moulding
,which is then transferred into a sintering
furnace.

most seat inserts ,regardless of material,are
first shrink , by refrigeration ,and then pressed
into the head , Dimensional tolerances are
always tight because the interference fit is
critical for their remaining securely in position
in service.

Potential modes of failure are loosening ,corrosion, wear, and material flow at high temperatures.

The requirements therefore are : a coefficient of thermal expansion compatible with that of the head material,dimensional and metallurgical stability at elevated temperatures,and resistance to loosening , Corrosion , and to abrasive, adhesive, and compressive wear.

Sintered powdered metal seats have the advantages of ease of production in large quantities,and material structures and compositions can be made up that are impossible by the normal alloying processes . For instance, solid lubricants can be incorporated into the powder mix.