I had the awful experience of firing up my recently installed 5.7 tpi yesterday to hear a deep knock low on the engine.I could press against the oil pan on the pass side lightly and it would change pitch ,like the crank is "right there" .I don't know what I could have done to this powerplant to bring this on with only 1,400 miles on the remanufactured engine ,so I would feel better in a way if I knew some of the possible ways that bearings are "taken out" BTW the oil pressure was solid ever since I first spun it up before firing the engine for the first time.I realize It is best if I just pull it out and get the damage accesed by a knowledgable person,but as exciting as it was to install fire and enjoy for three months it is a huge downer to be pulling it back out.Any thoughts would be appreciated.

 

who did the rebuild?
Sounds like a spun bearing. Chances are it's a screwed up build or something.
you can remove the motor mount bolts, jack up the motor high high high, and remove the oil pan. Then check your main bearings and rod bearings. You'll probably find the source of your problem there. Then you can justify pulling the motor for the rebuild. Then again, you might find it's something else, and since you haven't totally pulled the motor yet, you didn't waste a schwack of time.

 

NO, NO, NO!!! I've done this !!!
If you dent the bottom of the oil pan during installation the crank will hit on it sounding just like a knock. (front part of the pan)
The secret is you pressing on the oil pan and it changing pitch.
Don't pull that engine needlessly.
Pull the pan instead.

 

These guys have a good idea. unbolt your exhaust y-pipe and pull the distributor and jack the motor up. Then drop the pan and see what you have.