bring dampener to 15 BTDC. screw in piston stop till it contact the piston. turn crank back CCW till it stops again. you want it to stop on 15 ATDC. go back/forth 1 time to double check. if it stops on 13 then make a new white paint mark (1) degree on the side of the OE slit (I forget which side). repeat the test. You want the same degrees on each side. EDIT (1) degree is 0.0632683" or use the dampener as a ruler.