Edelbrock heads - acceptable tolerances

FYI.

On the engine line that I worked on, we had to keep the tolerance for the valve seat out of roundness to 13 microns (.013 mm - about the diameter of a hair or less). That is how much the seat can be off of a perfect circle. Even with dedicated tooling/machines, we still struggled to keep that tolerance.

You also have to keep the concentricity to the valve guide held tightly as that will also affect the valve seating. Concentricity, then roundness. Concentricity is how well the center of the valve guide is aligned to the center of the seat. Roundness is how far off a perfect circle that the seat is. They both have to be kept to a minimum.