So I wrecked my bike a couple of months ago and it sat with no oil or gas in it. I've noticed surface rust in a few "sensitive" places such as the starter clutch assembly. I'm wondering if there is anything I should do before completing final reassembly of the alternator/cover assembly to address the rust. What I can see doesn't concern me (what I can see is in a non-wear area.) I am more concerned with rust in places like the cylinder/valve area(s) Any thoughts? Temperatures have ranged from just below freezing to near 80f. Humidity has ranged from bone-dry to near sweaty armpit conditions. None of the rust I see has yet to flake or scale, its just on the surface.
My thought would be unless the engine has been sitting open and exposed you don't have much to worry about internally. If it were mine, I would clean off everything that's exposed and showing corrosion, fill it with oil and run briefly for a few minutes, drain that oil and fill with a fresh batch, then maybe do another oil and filter change after putting a 100 miles on it or so.
You might look inside the gas tank though, possible for rust to grow in an empty tank over time and that would probably involve having the tank professionally cleaned. I've seen that in older bikes anyway, probably not in a couple month's time though.
There are certainly guys on here that know far more about the inner workings of the 919 engine, so hopefully you'll hear from them as well. I assume this is your 919 we're talking about, right?
One question I just thought of for one of our mechanic members, is there a danger in firing up an engine that's been sitting awhile without any oil? Should some type of pre-lube be attempted? Can you squirt oil in the plug holes like an old car and turn the engine over by hand somehow?