Dumb question? IDK

if i have a crank that has already been balanced and i buy new pistons and connecting rods do i have to get the crank i have rebalanced or am i a dummy could someone explain what a machine shop does when you pay them to balance something? thanks-

To balance and engine the entire rotating assembly (pistons, crank, rods) need to balanced together as a set. The rods are weight matched as are the pistons. There are places on the rods and pistons where they can remove metal to get them all to weigh the same.

And no, it wasn't a dumb question.

To balance and engine the entire rotating assembly (pistons, crank, rods) need to balanced together as a set. The rods are weight matched as are the pistons. There are places on the rods and pistons where they can remove metal to get them all to weigh the same.

And no, it wasn't a dumb question.

hey man thanks for the reply so does this mean if the crank is already balanced then i need to have it rebalanced with the new set up or that all i need to have balanced are the pistons and rods?

You will have to have all of the parts together balanced.
I love wikipedia, here is a link, click me (http://en.wikipedia.org/wiki/Engine_balance)

personally id have it rebalanced,anytime you add anythign to the rotating assembly i think it should be rebalanced even if the pistons and rods are weight matched

anytime you add anythign to the rotating assembly i think it should be rebalanced even if the pistons and rods are weight matched

To include replacing a bad piston??? ANYTHING? Or are you talking on a rebuild and replacing entire sets of stuff... rods, pistons, etc? Doesn't include a new cam does it?

personally if your replacing one piston it probaly wouldnt be a bad idea to replace em all and do rings, and yes i think it should be balanced, usually around 150$ for the machine shop to do it too

To include replacing a bad piston??? ANYTHING? Or are you talking on a rebuild and replacing entire sets of stuff... rods, pistons, etc? Doesn't include a new cam does it?
Replacing a bad piston shouldn't be a problem as long as you had written down the weights of all of the pistons and their locations so you can be sure of getting the right weight in the right place (this is a non race engine, for a race engine then rebalance it all). If you were replacing even a single rod, then yes, rebalance the entire rotating assembly.
No, the cam isn't included, just the rotating assembly, which consists of: crank, rods, pistons, flexplate/flywheel and harmonic balancer. The higher performance the engine the more critical it is to have all parts balanced together. On a "hot" street engine you could get away with replacing a harmonic balancer or a flexplate/fly wheel or a single piston without rebalancing. But if I were pushing over 500 HP from the engine, I would rebalance for any single part replacement of the rotating assembly.