does a 400 crank with a 2.50 pilot for flex plate need a external balanced flex plate
 

When I bought my engine it was a 72 block and a crank out of a newer 400 with the small hub on the back. I am chasing a noise and the question came up does this need a weighted flex plate or not.

Can someone shed some light on that. I put a standard harmonic balancer on it.

Thanks
Greg

As far as I know the answer is no, the only externally balanced Pontiac V8's we the 301 & 265's of 1977-1981 vintage.

The factory flex plates are external balance -missing one hole. I would assume the factory cast iron flywheels also are. Depends on if the machine shop who built it balanced it for a neutral balance flywheel.