but the middle two positions on both sides of the center main bearing (the third of 5 mains) did not have any counterweight. Because these positions are located close to the center of engine, they contribute less to countering any rocking motions - hence the use of external balance weights (e.g. in the crank nose pulley), which requires less extra mass for the same balancing effect.

However, the uneven firing in each bank (see below), as well as the 90° piston phases themselves, do contribute to torsion in the crankshaft which can be