Did you put the 340 crank into your 318 or are you just going off the casting numbers on the crankshaft. A 340 has heavier rods and pistons than a 318 so it is balanced different even though it is neutral balanced.
It is a 340 crank shaft in a 318 with all 318 rods and pistons.
However they all spent time in an engine builder's shop together and he did his magic to make sure they would all work together.
I thought the harmonic balancer off the 318 was fine (thanks for verifying what I was hoping) but at some point with checking the timing I realized it spun on the rubber. And driving it i feel a vibration, its hard to describe, but it starts small then vibrates up harder, then drops small and vibrates up harder, over and over and over and the instances increase with RPMs.
