what could it be this time? 3100 miles after bottom end rebuild due to spun bearing and 2800 miles after a busted valve spring

http://www.youtube.com/watch?v=Rx7W8dRwkrw

 

sounds like a spun rod bearing and that knock sounds like piston hitting head. I am all to familar with that sound it happen to my lt1 car.

 

spun bearing number 2 is thats true... i never spun my car past 5k rpm...

 

That doesn't necessarily matter.

What has the oil pressure been like?

 

when you rebuilt it did you get all the rods reground and the crank reground and did you replace all bearings.

 

replaced the crank and rod and bearings

 

40 at running temp

 

you said replaced a rod or did you replace them all. If not some could be out of round. If you reused the other rods did you have them checked out by a machine shop. Also did you have your block and main caps checked .

 

But was it done right? When you have a bearing go out the proper way to rebuild is to totally tear the motor down to the bare block, pull all the oil gallery plugs, and have it hot tank washed at a machine shop. When you get it back you then need to get out your rifle cleaning kit and brush out all of the oil passages, rinse with water, then blow out with air. Only then will you be sure that all of the debris from the ruined bearing is out of the motor.
If you don't do this then there is a chance of debris blocking oil to a bearing and having a repeat of the bearing failure.

 

Amen to what Al says. I have seen many a rebuild end up the same way.

How much of the work was done by the shop on this motor and how much was done by yourself? What did you have done to the block in the rebuild?

 

Sounds like it's dead to me.