Resurfacing cylinder head
 

Is there a max amount of times you can resurface a cylinder head?

Three.

(Assuming that each time takes off 1/3 of the total depth of cut permissible before the head is no longer serviceable. If each pass removes 1/5 of the permissible depth of cut, then five.)

so after 3 the head is basically garbage?? Probably better to buy another head then?? maybe?

Three is a completely arbitrary number which I pulled out of the air in order to illustrate that it's not about the number of operations, it's about the total amount of material removed. Basically, the part in parenthesis. You could junk a head in a single pass if you cut it too much, or you could resurface it ten times if you're just barely breathing upon it with the grinding wheel. (Not that I can think of a valid reason to re-surface a head that lightly.)

The point is that there is not a set number of times that a head can be re-surfaced. It's all about how much material has been removed in total. Specs vary by model. I happen to have the BP manual here in front of me, and it states that the minimum height of the head is 133.8mm. Obviously, factory service manuals tend to be a tad conservative, as they're written from the point of view of a warranty-honoring dealership service department. How much tallness can be deducted from the head before it becomes serviceable is mostly about the relationship between yourself, your machinist, and the resulting static compression ratio.

There is a factory service limit which I do not know off hand. My recommendation for a boosted application is no more then .020". If the head needs more then .008" to clean because it is warped it should be straightened first otherwise the cams will bind.

what would be a result of a head that is resurfaced too much? Pistons hitting valves?

too much compression, altered valve timing, slack timing belt... and yes pistons hitting valves, depending on your piston dome, valve size and cam..