200x liquid rust in cylinder head???

[200xkwit]

I pulled apart my 200x motor to change the bottom end gaskets b/c they were leaking and upon taking the piston out of the cylinder I noticed that the top of the piston was black... but not like a carbon black (i couldnt wipe it off) whats that mean? but mainly im concernd that ther was like a liquid rust on the cylinder wall that wiped off but the cross hatch marks are gone too. I only have like 20 hours max on this top end. also to make matters worse one of my piston rings was frozen in its ring slot (wouldnt spring in and out) ended up brakeing that ring out and im ordering new rings soon but whats the deal witht his rust do I have to get my cylinder rebored? is rust abrasive?

[Mr. Sandman]

The last time I checked, the 200X wasn't water cooled so the question is how did the water get in there? If you pressure wash your bike with a hose, don't blast it with a solid jet of water as this is the most likly culprit. Even with good sealing gaskets, a blast of water can and will find it's way in. You also mentioned that the bottom end gaskets were leaking so this is also a way for water to find it's way in as water is thinner than oil.

As for your questions, black carbon that will not rub off the top of the piston is normal. The rust should not be abrasive to the point that you need to rebore, but check for scars, lines, grooves, etc. If it's just a light coat of rust that wipes out, a quick going over with 800 grit or finer wet/dry sand paper will do the trick.