Balance Shaft
| ITEM | DESCRIPTION |
|---|---|
| 1 | Upper housing |
| 2 | Location dowel (5 off) |
| 3 | Oil supply gallery |
| 4 | Intermediate gear - Driven balance shaft |
| 5 | Driven gear - Driven balance shaft |
| 6 | Idle gear - Idle balance shaft |
| 7 | Bolt (6 off) |
| 8 | Lower housing |
| 9 | Dowel (2 off) |
| 10 | Bearing shell - lower (4 off) |
| 11 | Balance shaft - driven |
| 12 | Balance shaft - idle |
| 13 | Bearing shell - upper (4 off) |
The balance shaft assembly comprises two eccentric weighted shafts which oppose vibrations created by the engine's rotating components. The balance shafts are driven off a 96 tooth ring gear located on the crankshaft which rotates a 48 tooth driven gear on the driven balance shaft.
The two balance shafts rotate in opposite directions, driven at twice the speed of the crankshaft. The equally sized eccentric weights are phased so that the inertia reaction to their counter-rotation cancels out vibration caused by the engine in both the horizontal and vertical planes.
Rotation of the driven gear is transferred by a second intermediate gear on the driven balance shaft to an idler gear on the idle balance shaft, which rotates at the same speed, but in the opposite direction.
The balance shafts are located on split shell bearings which are located in the upper and lower housings. An oil feed from the cylinder block supplies drillings in the lower housing to lubricate the shell bearings and the shafts.
The complete balance shaft assembly is attached to four bosses in the cylinder block by four bolts. Shims are positioned between the four bosses and the balance shaft assembly to obtain the correct meshing of the crankshaft ring gear and the balance shaft driven gear. The balance shaft must also be timed to crankshaft by positioning the crankshaft at Top Dead Center (TDC) and aligning a mark on each balance shaft.
Refer to: Engine - DESCRIPTION AND OPERATION .