piston discoloration

[Mike Horton]

I hope everyone is ok with me asking a question about a modern bike (KTM 200xc 2 stroke)? I have tried on ktmtalk but no success. I know if I can get a answer it will be here - lots and lots of experience. I had the header pipe and reeds out of my bike today and looking into the cylinder I noticed the skirt on the exhaust side and inside the piston on the intake side that the aluminum is discolored to a blue-green tint. I have never since this before. Any ideas what has caused this ? Premix is red and coolant blue ...?? Any thoughts would be appreciated. Bike is running great. Thanks

[Kip Kern]

Do a compression test and compair it to manufacture specifications, that should get you started!  Throttle wide open and kill switch on then kick the hell out of it!

[Mike Lenz]

Is your filter oil blue/green?  Maybe too much on filter??

[joe novak]

How long, or how many riding/racing hours has it been since you have checked the top end of the engine?  If the piston rings are worn, the combusted fuel/oil mix will blow-by the rings.  This will eventually stain the intake and exhaust skirt of the piston.   Check for liquid in the carb boot between the carb and air box.  This is a good indicator of blow-by.   Also, great ideas of Mike and Kip.

[Mike Horton]

Thanks for the ideas. The bike only has about 20 hours on a new top end including replate of cylinder. Also had port work and the head cut. Its is running terrific. Only thing different on this top end (#3) is a Athena forged piston instead of KTM OEM which is cast. Oh by the way. filter oil is no-toil which is red. Thanks

[joe novak]

How many thousands of an inch was removed from the head?  I am not familiar with how the head attaches to the cylinder.  Are there studs mounted in the top of the cylinder with washers and nuts to secure the head?  It may be possible that there is some obstruction which does not allow the head to be sealed correctly.  Sometimes the head gasket only leaks when it gets hot.   Are you losing coolant from your system?