Cosigned on the improperly tightened crank bolt.
The bolt presses the crank pulley/ dampener and the timing gear against the shoulder at the end of the crank snout preventing movement. The key is only for alignment. Insufficient torque of the crank bolt will allow movement which over time erodes the crank pulley where it fits around the crank, and the back of the timing gear where it presses against the shoulder at the back of the crank snout. I have a cancerous set that I can take pictures of and show you what I mean.
The rust dust is the result of this erosion of parts. As the parts erode, the resultant metal dust is dispersed around the ancillary drive and timing drive, where it accumulates and oxidizes as a result of being exposed to the atmosphere.
It is important to remember that even though there's a slight interference fit between the two pulleys and the crank snout, that interference is not what keeps the parts from spinning. The pressure a properly torqued crank bolt exerts against the parts into that shoulder on the crank is what keeps things in place. You don't hit the mark when you're torquing down that bolt, and you can kiss your crankshaft, pulley, key and sprocket goodbye.
