i can't get the center screw off ...i've only tried by hand so far as i don't want to strip the head of the screw ..its on extremely tight ...i have a 310...i think they only did the 310 in canada ....any advice would be appreciated Ty.....it says the cutting system is blocked ....i cleaned it out changed the blades but still keeps saying this and the disk is not spinning very freely ...hence the need to remove that center screw and take a look ...