How to balance a split pin crank?

[bigdwg03]

I'm trying to get into the automotive machining field, I've only taken a few basic machine courses but I've been wondering how you balance a split pin crank I know its different because each rod has it's own journal. Can anyone explain how it's done? I've asked a few people and got all different answers. Any info would help.
Thanks

 

[bison]

The simple answer is you can't balance it in both planes. The factory underbalanced them and used the stock engine mounts to absorb the imbalance. With solid mounts builders typically use 50% weights. Some builders go slightly over 50%.

 

[bigdwg03]

Thanks for the info! I like the manwhore line haha

 

[David Husek]

I'm trying to get into the automotive machining field, I've only taken a few basic machine courses but I've been wondering how you balance a split pin crank I know its different because each rod has it's own journal. Can anyone explain how it's done? I've asked a few people and got all different answers. Any info would help.
Thanks

I am assuming you are referring to a Buick V6 even fire crank.
.
When a crankshaft is balanced, the actual rods and pistons cannot be used in the balancing machine, so they must be simulated. This simulated weight is called the bobweight The Buick v6 will use a 36.6% reciprocating factor to calculate the bobweight. Once the bobweight is calculated, weights are bolted onto each rod journals to simulate the weight of the rods and pistons during the balancing process. The balancer and flywheel will also need to be installed if being externally balanced. At this point, the balancing procedure is no different than any other balance operation in short, adding or removing weight. There is much more to this art than a quick summary though. Hope this helps.

 

[bigdwg03]

Are you saying use 36% of the bob weight? Why not 50% as bison stated?

 

[David Husek]

Are you saying use 36% of the bob weight? Why not 50% as bison stated?

Yes, you will use 36.6%. Bison states “The factory underbalanced them (36.6%) and used the stock engine mounts to absorb the imbalance. With solid mounts builders typically use 50% weights.”

 

[bigdwg03]

Oooh gotcha makes sense
Thanks!