Hi all.    A month ago I asked what possible causes there was for a younger (5600 hour)  JD 8420 motor to fail.   Got into it today and a  portion of the no. 5 piston flaked off the top, by the rings, allowing blowby.  Thankfully I was not working it hard at the time, and heard a little raspiness, and saw some blowby on a front tire.  .  Mechanic said injectors were good, piston just decided to no longer stay intact.  Particles did float around for the 3 minute trip home, but hopefully there will be no further damage.  She will get new sleeves, pistons, and a complete head job.  Could be lots worse.