yea mahle pistons are coated. The reason FRM sleeves are hard to hone is because on top of the fiber material there is a coat of chromoly steel. Thats what the piston rings contact. The FRM itself is too soft. If you hone the chromoly too thin it will wear though to the FRM material and your engine will have massive amounts of blow-by and will lose compression very quickly.Originally Posted by HatchHero