i have a 2004 yz250f and about 5 weeks ago while i was riding all the sudden the bike starts making this knocking sound (kinda sounded like piston slap). I shut it off right away and kicked it slowly and felt something scraping when i kicked it. well i decided to put in a new top end (piston, cam chain) while i had the top end off i inspected the rod and crank bearings all seamed perfect. no play and very loose. well i put it all back togeather tonight and after filling it with oil and coolent i kicked it slowly a few times and the scraping was still there:banghead: . I havn't started it yet im too scared to. Have any of you had this happen? what do you guys think it could be. thanks for any help!