Did an engine swap from a 305 to 400sb. I fired it up and I'm hearin a fast and loud knock. I thought a rod cause the noise comes from the oil pan but I have great oil pressure. I've pulled the valve covers and the lifters aren't makin the noise and they're gettin good oil. In order to keep the tranny the 305 used I had to put a balancing plate and I was wondering if somehow the flywheel was too far back and a bolt could be knockin or something.

 

Get a stethoscope and inspect the area while it's running. It's possible you have a loose flex plate bolt.

 

I listened with a screw driver to the bell-housing and the oil pan. the sounds coming from the oil pan. but if it is a flywheel bolt then the noise wouldn't com from the bell-housing anyway cause it's connected to the crank right?

 

Flywheel = manual trans.
Flexplate = automatic trans.
Just to be sure first, which one do you have?

 

Any noise generated from the torque converter or flex plate would be heard from the bell housing, and possibly slightly from the oil pan. If it's coming primarily from the oil pan, it's a rod or a main bearing. Most likely a rod.

 

http://www.kmjent.com/cart/product.php?productid=612
This one says it will not work will all flywheels......

 

It's a manual and I made sure to put the balancing plate on the back of the flywheel. If it's most likely a rod then why 60 psi oil pressure at idle??

 

It could be piston slap, which is caused by too much piston to cylinder wall clearance allowing the piston to rock more than usual.
And that would have no direct bearing on your oil pressure (no pun intended...ok, maybe a little).
Is the noise worse when the engine is cold as compared to when it's hot? If it is, piston slap could be your problem because the pistons expand when they get hot, which closes the clearances somewhat.

 

Lol that was clever...

I've never heard what piston slap sounds like. The knock is really fast though and I haven't heard an audible change as the engine warms up.

In order for me to pull the engine and investigate I need to take the f-er to my friends house cause every time I pop the hood on a car here i get an eviction notice. So I'm getting insurance on it. Would it be okay to drive her a little ways with it knocking??

 

it probably is piston slap. my grandfather put a 400 sb in his 55 chevy and had the same problem. it turned out to be piston slap from 4 different piston that caused it to sound different and throw him of what it really was. depending on the clearance it should be fine but he had like .08 clearance in 2 or 3 cylinders which is only good for race motors not street cars so now that block is on the stand for sale.