Originally Posted by
merdith6
It looks like normal carbon oil stuff on the piston, a little bit dark though. I would clean it off. as for rust hell yeah cranks can rust. I see it all the time on all kinds of engines with different fuels too. Usually it's the rear bearing races and the crank that rust, not much else. I always use plenty of oil when not running them.
+1, if people havent seen a rusty crank, not sure what they have been looking at or perhaps live in a dry climate, if in London, you'll have rust!