So we just recently put new timing chains, tensioners, oil pump, etc on a 5.4 from a 2005 f150. Now it rattles especially when in reverse. My mechanic noticed that the flywheel moves about a 1/4 of an inch front to back and recommended I have it checked. After further inspection he noticed the crankshaft moves with it so its not the flywheel. Is there a spacer we neglected to put back on or is the gear for the timing chains on the crankshaft only go one way and we assembled it backwards? Where could this slack come from? I sure don't want to pull it all apart again just to look around.

 

The crankshaft thrust bearing is wiped out. Most likely that was the cause of your low oil pressure to the phasers and tensioners. The engine needs to be completely torn down and inspected. You might have damaged cam journals too which requires head replacement. Sorry but this isnt a patch job if you want it to last.