One of the most commonly serviced parts of an engine is the cylinder head. It is often removed either for modifications (such as porting), replaced with a different design, or to facilitate a repair (as when a head gasket fails). Regardless of the work being performed, the cylinder head requires special service to guarantee not only that the deck surface is true, but also proper valve action and sealing.
The cylinder head can be brought to the machine shop either assembled or disassembled. If you decide to disassemble the cylinder head yourself; keep the valves, locks, springs, and retainers together for each port. Do not throw everything into a box, but instead number each group of components with its location. For example, #1 intake, #7 exhaust. This will allow the machinist to diagnose any wear problems and perform accurate corrective procedures. Remember, when it comes to engines, every part tells a story.
Once the machine shop receives the cylinder head, they will do a visual inspection to look for damage, such as cracks and valve recession. When recession occurs the valve will actually pull through the cylinder head at the seat. This is shown on the surface the valve closes against. Next, the head will be taken apart and cleaned. Cast iron heads can be Magnafluxed using the same procedures that were established in Part 1 of this series. Aluminum cylinder heads need to be pressure checked using an application-specific machine to confirm no cracks exist.