after ur piston blew up did u take apart the bottom end and flush it out, sounds like you maybe have gotten a hunk of it back upt o the top end and bounce around for awhile, or a fuckin bearing, def split the cases, check all bearings, clean it out, new crank maybe if needed, true and weld it, new topend on ebay, they are goin cheap, and like dlnoss like reas said,