Technical Crank balancing question

The engine is in the shop and the crank has to be replaced. The rotating assembly has been balanced previously so I figured they could balance the new crank and that should be it but they tell me they have to do it all, take the rods off the pistons, the pins are pressed in, and go from there. This seems like overkill to me, but what do you more knowledgeable guys think. It's an Olds 455 that doesn't rev past 5500

 

The first step in understanding balancing is to understand how a crankshaft is balanced and what the purpose of the counterweights are. The counterweights are designed to offset the weight of the rod and pistons. Since different rods and different pistons are different weights, it is impossible to make a crankshaft that is balanced "right out of the box" for any rod and piston combination. All crankshafts must be balanced to your specific rod and piston combination.

 

If you have the previous balance "bob weight", give it to them and hopefully they should be able to balance it fine.

I know when I messed up and didn't buy 1/4" longer rods and had to have Lunati cam-cut my 496 crank, they asked for the "bob-weight" when they rebalanced it using heavy-metal.

pdq67

 

He could weigh the piston rod assemblies to get the bob weight [ maybe only dismantle one]
BUT................

If the engine shop has any integrity they would be asking you what they already asked you.
They would be relying on whether the previous job was any good [unless they did the previous balance job themselves]

I've seen a balance job done with a drill-press and grinder at home as a "swap-meet special" selling second hand balanced assemblies
Anybody can drill holes in a crank.... but drilling them to the correct depth in the right place takes a bit more skill

 

I'm pretty sure I have the balance card from the previous job buried away somewhere. I'll find that and then see what they say.
Olds cranks are external balance

 

Just because an engine is low RPM doesn't mean you don't need to balance it. A heavy rod assembly swinging a big arc will shake like a washing machine full of beach towels and tear itself apart.

 

[QUOTE
If the engine shop has any integrity they would be asking you what they already asked you.
They would be relying on whether the previous job was any good [unless they did the previous balance job QUOTE]

Exactly...... We never take for granted the work done at a previous shop

 

That's ALL you need is your old balance card; it will have all the info they need, unless all they're trying to do is up-sell you. I am Butch/56sedandelivery.