I hear this quite often, but I don't quite see how this is true. Each piston is hooked to a crankshaft, which is hooked to a flywheel. Even with a single pisto

I hear this quite often, but I don't quite see how this is true. Each piston is hooked to a crankshaft, which is hooked to a flywheel. Even with a single piston, the energy of it slowing down and reversing is absorbed in the flywheel, which is in turn used to propel it in the opposite direction. Add multiple pistons, and the energy of slowing down is again used to accelerate another piston. Just think of any spot on a wheel representing an arbitrary amount of mass. Spin the wheel, and the only thing slowing it down is friction -- not that spot constantly changing direction.