I have a 2007 kx250f that recently was rebuilt. The motor blew up a while back and we just replaced the cylinder piston crank bearings gaskets etc. Complete bottom end. But we started it up and it knocks about everytime the piston turns it sounds like. I have put different heads different cams messed with piston and pulled everything apart. Still knocks. I was wondering if anybody had an answer for me as too why this happens?