When you consider the crazy monkey motion of reciprocating internal combustion engines it is remarkable they work as well as they do. You have eight pistons and connecting rods doing a "do-si-do" ...
00:00 Intro 00:35 Motorcycle and car applications and firing intervals 05:00 Acceleration, Velocity and Force 07:58 Primary balance and vibrations explained 12:22 180° and 360° twins primary balance ...