I have bought some 3.905 pistons for a rebuild using the stock crank and rods, and I wondering do I have to re-balance everything or just the pistons?

 

you will rebalance everything. the pistons should be close to each other, but depends on what brand they are and how close tolerances the manufacturer says is allowable. my wiseco pistons were within 2 grams from the lightest to the heaviest.


the crank was originally designed for stock pistons and rods. sure, you can just put it all together. you may, or may not have a vibration.

i had my eagle crank balanced only. no vibrations here.

 

If its apart, I would get everything balanced. If you button it back up and its shaking then your not gona be happy.