i know this an old post but some stuff here scared me in a bad way,,, i work in an engine rebuild shop,,,the block guys get scared when theysee us with those schtchbrite discs, they are ok for some things,like valve covers or somethinlike that,very easy to mess somethin up,,i found like 400on up to 1000 grit on a palmsander,with some brakecleen is nice on aluminum,depending on how qwickyou want it cleanwhen i did this on my head,it almost retained the "rainbow" of a freshly milled head,,and use a wire wheel on cast iron,,,,thats what the rebuilders recommend,,stains dont hurt cast,,,,,,,,NEVER never glassbead ring areas of piston,,just dont bead them at all,,,,use either that cold carb dip,or zip strip/"gasket remover" ,,,,cold dip i have had that discolor pistons,,,,but for my tdi build,,i used zipstrip and wood slivers to clean ring lands,,tootthpicks work ok,,DONT use any metal utensial on pistons,,,plastic and wood is ok,,,my pistons cleaned up like new,,but it took 4 --5 applications,tooklike 3-4 hours ,,you mcanuse some toothbrushes,but they melt in the zipstrip after a while,,use it to get the heavy stuff off,,,you do not want to remove any metal from the lands by scraping,,happy building,,70% of engine building is cleaning and prepping,,,a fine wire wheel can be used on aluminum covers and stuff,like seal carriers,,if you are careful and easy on it,,dont stay in one spot for long,,itll dig a little,,carefulwith the rebuild,and itll runa long time with good power potential