The Microlon engine treatment works in two stages. First, the Microlon cleaning complex clears the engine of the carbon, varnish, and sludge that can accumulate through normal use. After the engine is clean, the Microlon film forms on the bearing surfaces. None of that process is inherently harmful to any engine. There have been a couple of cases where we have recommended that an engine not be treated, and those cases dealt with very old engines that were essentially held together by the gunk that Microlon will remove. Microlon Incorporated has full faith in its products and is proud to offer their customers a three-year unconditional money back guarantee.