Usually if the comp sprocket is bad or loose, it will give you a knocking noise like a bad rod bearing. It basically absorbs the power pulses from the crank to smooth out the power transmission through the primary chain using ramps that load and unload when the piston is forced down in the power stroke. There is a spring that forces the two halves together that gets compressed on each power stroke then unloads to give you a smoother ride. In other words it takes the shock out of the drive train.
