Home position is not at z max on delta

When I home, my z position is 253.3 whereas I set z max in marlin to 257. After homing, I can still move the z up but it just grinds against the endstops.
Cheers for all the help recently

I dont know for sure in marlin, but for repetier there is a option called "Endstop distance after homing" wich controls the distance of the carriages to the endstops after the homing has taken place (so the printer homes at the Z max distance minus that parameter). It's pretty useful for delta printers since when you move the effector horizontally, some carriage go up and the other goes down, so if your printer is touching the endstops, your effector can only move down.