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From The Saab Tech Wiki
=The Saab balance shaft system=
[[File:Balance_shafts.gif|thumb|none|Saab Balance Shaft System Illustration]]
Saab has used the balance-shaft principle to overcome the second-order inertial forces. Two balance shafts located with lateral symmetry on the sides of the engine block but at different heights above the crankshaft centreline incorporate eccentrically mounted balance weights. The shafts are driven by a chain and rotate in opposite directions to each other at twice the crankshaft speed.
