my nephew brought his 03 yz450f over for me to work on? had a high pitch rattle in the top end (at any rpm) and stated rachet type noise (liking chatter/popping out of forth gear). i tore it down first thing i found was the piston was broke off on one side where the clip holds the wrist pin in?? after further inspection i found the cranshaft black and blue around the rod bearing, showing signs that it was about to sieze at anytime ( although it ran and idled perferect) i split the cases, inspected all of the trans gears and shift forks (found the broken peice from the piston in the lower end) but all the gears and shift forks appear to be in good condition! i know where the noise was coming from (piston broken), i have never seen a piston break in this way any ideas as what could of caused this?? i am concerned about the trans popping in and out of 4th gear. is this common, have you heard of this or am i missing something in the trans. maybe the broken peice was going through the trans causing it to pop out, but i cannot see any witness marks in the gears indicating that is what happened?? any info or from you experience would be appreciated.