RE: New Supertigre G90 with scratches on the piston.
I would pull the head and backplate off and give it a good visual inspection for swarf (machining debris ) and flush it out with "jet spray" type carb cleaner. Use Q-tips to clean all the little nooks and crannies too...You'd probably be surprised at how many new engines have some sort of swarf in them.</p>
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If the scratches are not in the sleeve and ring, it should be OK.</p>