I'm fixing to change the timing belt on a 3000gt and after looking at several guides and sites on line i am confused about why they count the teeth on the cam sprockets before they install the new belt. Why cant i just line up the marks on the crankshaft and cam sprockets and slide the belt on?

 

Not sure why anyone is "counting teeth" either. The best way is to line up all the timing marks on the cams and use secial tool to lock the cams in place so they won't move when the belt is removed. Then they are all lined up for the new belt. If the cams aren't locked, the cams will spin when you remove the belt and you have to lined them all up again, making sure you rotated them in the correct direction so as not to damage valves. To get the cranskaft timed properly, its easier to rotate the crankshaft one tooth countercloskwise and slide the belt on the crank. It will go on much easier this way, and when you rotate the crank clockwise, evertyhing should line up and the belt be tight on the backside.