Recently rebuilt my motor, tried starting it up for the first time and it's turning really slow, dash lights are flickering on and off like crazy. It's just turning slow. Here's a video

 

Most likely 1 of 3 things
1- dead battery
2- valve train issue (cam out of time, or something missing so the valves are not opening closing correctly)
3- Crank bearings improperly sized (most likely)
-Was the crank turned or polished? If polished and you had originally sent it to be turned that the oversizing of the bearings the set aside is most likely incorrect.
I had a similar problem when I rebuilt and engine years ago.

 

I didn't do anything with the crank, I took it out, and out factory clearance bearings in, then put the crank back in.

 

If the battery has full power I would check your grounds. The flashing lights on the dash indicate "low" power in the electrical system and the computer is hunting for signals.

 

I found the ground I was missing. It was the engine ground. Comes from the back of the motor onto the body, a little high than the heat sheild. I hooked that up, the starter turned a little faster for about 3 revolutions, then stopped turning completely. Any ideas?

 

When I hooked the ground up the lights stopped flashing.