My 400 has a bad knock at starting, and at higher rpm's when reving in park. I have had lifter knocks before, and that isn't it. It sounds like a piston or rod its falling apart or something. Any suggestions? Thanks.

 

How's your oil pressure... Probley going to need a rebuild.
Pull it out send it to a machine shop if the crank isn't to beat up they may just get away with polishing it up and new bearing. rework the rods, clean up the bore's some and install new rings.