This is for 340 builders

66silverfish said

Pistons are going to be replaced. Was going to balance the entire rotating assembly, dampener, flex plate and conveter. Sounds like I will be replacing everything. If I do keep the crank, heavy metal will have to be added during the balance. Do they still use lead or is there something else they use these days?

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I've had over a dozen 340's and the cranks are the same, you will have to have the rotating assembly balanced anyway so the weight difference won't matter but most new pistons are lighter than the stock ones so the weight difference won't be much if any. To add weight they just drill a hole and insert a tungsten weight and weld it in. Adding weight is common when balancing an engine, especially if you go with pop up pistons or the engine was bored because the pistons are heavier than the originals.

As far as the rods, the rods that come in most 318's are a lighter rod, Most steel crank 318's came out of trucks and the rods in the 318's with steel cranks are usually the same as the 340, there is a part number on the side of the rod that tells you what they are. Also most pre 72 truck engines had full floating pins and they are most of the time the same 340 rod.

I have a set of 69 340 rods I had redone for another engine, I will see if I can get the number off of them but the part numbers did change frequently over the 6 year run of the 340 so that might not help much, I know I've seen several different part numbers myself. There is a Direct Connection book that was published back in the late 70's that has most the small block engine part numbers and tells you which ones are which and which ones to use.