Method of manufacturing a hollow poppet valve

A method of manufacturing a hollow poppet valve having an internal cavity that extends from within a valve head into a stem portion of the hollow poppet valve and is filled with a coolant, the method comprising:

• a coolant-rod forming step including extruding a linear clayish coolant from a nozzle of an extruder and cutting the linear coolant into coolant rods of a predetermined length;
• a plurality of coolant-rod inserting steps each including inserting the coolant rod into a hole of an intermediate valve product that corresponds to the internal cavity of the hollow poppet valve, through an open end of the hole, such that more than one coolant rod is inserted into the hole of the intermediate valve product;
• a coolant-rod pressurizing step including pressurizing each of the coolant rods in the hole with a pressing rod, thereby plastically deforming the coolant rods, following insertion of each coolant rod;
• and
• a sealing step for sealing the open end of the hole.