REMOVAL & INSTALLATION
Removal or cutting of the valve seats is a very complex machining process which can only be performed with expensive equipment and specific knowledge and skills not generally available to the common DIY mechanic. Take all heads to a reputable and able automotive machinist to have the seats either recut or replaced with new ones.
Valve seats are removed in various different ways, such as drilling out the old seat and pressing in a new seat or by pressing the old seat out and the new one back in with the head heated to a specific temperature.
On most applications, the seat is installed after the head is heated to 482°F (250°C). The room temperature seat is pressed (not hammered) into the heated head. As the head cools, it grips the seat very tightly.
After the seat is installed, the metal must be allowed to return to normal temperatures slowly. Resist any temptation to hurry the heating or cooling; sudden temperature change can cause the metal to crack. Simply let the head sit, usually on the press or workbench for a few hours.
After the head has returned to normal temperature, the new seat insert must be machined to the correct angles. The valve is then inserted and the valve and seat lapped with compound to assure perfect contact.
The seats in aluminum cylinder heads are integral and so can only be machined to specification, not replaced. If a seat is too worn to be brought to specification, the head must be replaced.