PURPOSE: To counterbalance the secondary unbalanced force of an engine by providing 1st. and 2nd balancer shafts, parallel to a crankshaft, rotated in the same and the opposite direction to the crankshaft with an angular velocity of two times of that of the crankshaft respectively and attaching three eccentric weights of different mass to both balancer shafts respectively.

CONSTITUTION: The 1st. balancer 4 is provided in an oil pan 6 and rotated by a crankshaft 2 in the same direction of which with an angular velocity of two times of that of which, and constructed with a balancer shaft 8 parallel to the shaft 2 and an eccentric weight 8a attached to the shaft 8. Where, the weight 8a is attached to the shaft 8 toward the under side of the central axis of rotation. And a balancer 5 is provided in a head cover 9 of the 1st. cylinder row 3-1 and rotated by the shaft 2 in the opposite direction of which with an angular velocity of two times of that of which, and constructed with a balancer shaft 12 parallel to the shaft 2 and an eccentric weight 12a attached to the shaft 12. Where, the weight 12 is attached to the shaft 12 toward the upper side of the central axis of rotation.