Used crankshaft. Balance it or not?

[Misaeus]

A friend of mine needs to replace the crankshaft of his 440.
He found a used stock steel one at a reasonable price.
Can the crank be instaled without rebalancing it? or a balance job is mandatory?

Thanks in advance

 

[19mopar65]

I believe all the big blocks with steel cranks were internally balanced so I guess I would probably get it balanced IMO

 

[daredevil]

if its ever been rebuilt the bob weight may have changed. balance it. especially if changing from cast

 

[Meep-Meep]

A friend of mine needs to replace the crankshaft of his 440.
He found a used stock steel one at a reasonable price.
Can the crank be instaled without rebalancing it? or a balance job is mandatory?

Thanks in advance

If you are referring to "just balancing the crank and all should be well" then that's not the whole story. The entire rotating assembly is balanced and the bob weights are calculated as half the weight of the piston and rod assy because the piston mass is not considered part of the rotating assembly 50% of the time while the crank is turning. Make sense? Therefore, you will need to know the weight of one piston and rod assy for a V8 to calculate the bob weight. For normal rebuilds you can get standard replacement pistons and be fine because they should be within the factory piston weight tolerance, and swapping in a crank could work too assuming all factory parts are used and all engines were balanced within said tolerance from the factory, but it's now many years later and nearly everything we touch has been messed with to some degree, sooooooo.......

If the engine you are working on has forged pistons, or any other than exact stock replacement, then balancing is mandatory and you should pull at least one piston assy so the shop can get a new bob weight number.

I didn't mean to get all geeked out but I rebuild and balance precision rotating machinery for a living so I have to be up on the subject.

 

[MarPar]

Hey Meep, u almost sound like you know what you're talking bout! LOL:rolling:

 

[Meep-Meep]

And I want my customers to think that too :rolling::rolling::rolling:

 

[69 Runner]

What they said. COULD you do it....yes. Is it a good idea? Only if I had a fresh motor ready to go in already