The piston cleaned up pretty good inside the Chem-Dip, but did have a few areas of very stubborn carbon that needed to be scraped off with patience. 2 down and 4 to go. Should have a couple more removed tomorrow and soaking overnight. I am a little surprised that the quality of machining on the pistons seems rough, but I also think these are stock pistons and NOT a proprietary UL Power part. Makes me tempted to see if there is a higher quality piston out there that could be used instead :)