it all depends on the year of the U13 motor.
It will either start
-5, 0, 5, 10, 15
or
0, 5, 10, 15
The best thing to do is to put a long screwdriver down in the number one piston hole or a long skinny stick and turn the motor untill it goes all the way to the top the zero mark will line up.
I will make a gues that yours is 0, 5, 10, 15