if i already have a factory GM 5.7 crank and say i ordered a rotating assembly from someone like Texas-speed and they throw the whole kit together and balance everything with a stock crank, and then they send me everything but the crank they used to balance it would i be able to just use the used crank i already have or is it more complicated then that? hope this question makes sense. thanks.

 

Well the issue is there are counterweights on the crank. And those are adjusted to balance the assembly. So if you don't use the crank they provide, then you don't have the right counterweights installed and in the right areas. So that defeats the purpose.

 

ok. i figured it was something like that. just thought i might be able to get lucky and save myself the money on the crank. thanks for the response

 

What you're balancing is the crank, using the weights of the rods and pistons. If they balance a crank and then keep it, that doesn't help you.

If the rods and pistons are balanced, then what they've done (you hope) is measure the weight of the pistons, rod big end, and rod small end. Then make sure they all match. If they do that, be sure and get those three sets of numbers; you'll need that info to balance your crank.