Yamato HCM 650 Manual Del Usuario página 31

A. Press on the centre of the longest span on the belt with moderate finger
pressure. Then measure the deflection distance, the distance that the
belt moved. The belt should deflect anywhere from 1/2" to 3/4".
B. If the belt deflects too much, tighten belt by loosening the motor
mounting bolts and moving the motor away from the other pulley
slightly. Secure motor mounting bolts and retest tension. If the belt is
too long to be properly tensioned, it must be replaced.
C. If the belt deflects too little, loosen the motor bracket bolts and lift it
upward. Secure motor mounting bracket and retest tension.
5. Before use, replace belt motor cover.