Forces, torques and moments applied to the multi-cylinder engine and its crankshaft
4-Cylinder Engine and Multi-Cyclinder Engines Torque Fluctuation

The rotational inertia forces F_i/rot associated with each cylinder rotate with the crankshaft and generate vertical forces of order 1 and horizontal forces of order 1. Depending on the number of cylinders and crankshaft configuration, these forces can generate sifting and ramming movements of order 1, as well as galloping and yawing movements also of order 1.

The alternative inertial forces F_i/alt linked to each of the cylinders are directed along the axis (O, z) and can be broken down into sums of sinusoidal forces of orders 1, 2, 4, 6... They generate rammer movements as well as galloping movements of orders 1, 2, 4, 6...

Finally, the moments of inertia M_i/alt and gas M_g associated with each cylinder compound their effects on the multi-cylinder engine and impose roll motions of orders 0.5, 1, 1.5, 2, 2.5... around the crankshaft axis.