Hello everyone,
My 2004 350z had been running rough with the same symptoms that it had before the valve cover gasket was changed on the right (driver's side), so I decided to changed the valve cover gasket on the left side. There was a small amount of oil in the middle spark plug well, so i replaced the spark plug boot too. The car was put back together and when it started, the most horrible screeching noise that sounded like metal on metal began just after start-up. I couldn't bear to let the car run for more than a couple seconds. I took everything apart again and found some gashes in the crankshaft area. (Sorry I don't know the specific names of the crankshaft parts) I followed the DIY valve cover gasket replacement thread from here step by step. I also covered the area with a towel, to make sure nothing fell in it. My question is what could have possibly caused that noise? Or the damage? Any help would be greatly appreciated!!

 

Marks on the cam look normal, there are usually grinding marks between some of the lobes. Not sure what to say about the gouge on the inside of the head.

 

Wrench, socket, screw driver, ???????????

 

Ok, so besides something falling into the crankshaft area, there is no other reason for the engine to make a metal on metal screeching sound?

 

Those are camshafts not a crankshaft. Cam looks normal, but ya that gouge looks wtf. What did you drop in there?

 

I have no idea! I tried to be careful with all the bolts I took off. I don't even know how to search for whatever could have fallen in there. Anyways, thanks for the help everyone.