There are several factors which affect the amount of material that can be removed from the surface of a cylinder head. These include valve projections, surface flatness and finish. Measure these areas as well as the cylinder head minimum thickness dimensions whenever you recondition the head to block mating surface.
Before cleaning or machining of the cylinder head bottom deck, remove fuel injection nozzles/adapters from the head. On occasion, intake and exhaust valves may also require removal. Machining this surface can be accomplished with a mill, surface broach machine or surface grinder.
NOTE: Remove the minimum amount of material necessary to make the repair. Minimum head thickness following machining is 98.89 mm (3.893 in).
Machined surfaces must be smooth to form a good seal. The surface finish of the cylinder head faces must be as smooth as a new head after machining. Cylinder head flatness must not vary more than 0.10 mm (0.004 in) overall, or 0.05 mm (0.002 in) for any 152 mm (6.0 in) span.
Cylinder head flatness can be measured by using a 610 mm (24 in) straight edge for measuring the total length flatness and a 152 mm (6 in) straight edge for measuring across the sealing surface.
* Place the straight edge on the sealing surface.
* Use the feeler gauge and very carefully slide it under the straight edge.
NOTE: Clean machining debris from internal head passages prior to reassembly.
After the cylinder head has been reconditioned, you must measure the valve projection. The maximum and minimum projection specifications for intake and exhaust valves are listed in the Service Manual for the engine. Excessive projection can cause the valve head to contact the piston during engine operation.