1970 340 Balance Problem...Bottom Line

340's were all internally balanced through '71 and a few '72's made it through. Balancer should be flat with no counterweight and converter should be neutral with a neutral flexplate. Balancer should look like any 318 balancer. '72-'73 had the counterweight cast into the balancer that said something like "For 340 cast crank only". This counterweight is smaller than what was found on the earlier 360's. Later 360's had weight removed from the opposite side and the '93 & newer 360 Magnums are different are different too. B&M makes flexplates that have the correct balance built into them for each different externally balanced application so the readily available neutral balanced aftermarket converters can be installed without the hassle of positioning and welding the correct weight on them.

A cast crank will have a small, sharp cast flash line running up and down the crank. Forged cranks have a 1/4" or so machined-like line running the length of it.