Looking For High End Crank Balancing In States Surrounding Iowa

[Hemi Joel]

As a guy who has never balanced a crank, I have a question: If the counterweight counterbalances the reciprocating motion of the pistons and rods, and the pistons and rods in a performance motor are lighter than stock, why do you add weight to the counterweights to balance the crank in a performance build? it would seem that weight would need to be removed  to compensate for the lighter reciprocating parts.

[pbf777]

      Yes, if the crankshaft in question had been balanced of the same adopted learned procedural calculations process, properly, then if the sum of the revolving and reciprocating weight mass were to be reduced, then the "bob-weight" calculation would be less and yes the counter-weight value in the crankshaft would need to reduced commensurately.   

      Now note, that in some instances of peculiarity, individuals will stray from the generally recommended and practiced mathematical calculating process to create values other than that considered the norm, but these generally are to address unique scenarios.   

      Scott.

[blykins]

As a guy who has never balanced a crank, I have a question: If the counterweight counterbalances the reciprocating motion of the pistons and rods, and the pistons and rods in a performance motor are lighter than stock, why do you add weight to the counterweights to balance the crank in a performance build? it would seem that weight would need to be removed  to compensate for the lighter reciprocating parts.

Manufacturers design a crank for a specific bobweight.  Sometimes the bobweight doesn't match the parts that are available.  Also, some cranks are designed for external balance and then guys go and internally balance them. 

[My427stang]

As a guy who has never balanced a crank, I have a question: If the counterweight counterbalances the reciprocating motion of the pistons and rods, and the pistons and rods in a performance motor are lighter than stock, why do you add weight to the counterweights to balance the crank in a performance build? it would seem that weight would need to be removed  to compensate for the lighter reciprocating parts.

Often the H-beam rod and bigger bolts, etc weigh more than factory parts, or the crank isn't designed to be balanced the way you try to balance it (like internally balancing a 428)

I have a 390 crank I ran in my Mustang years ago that we added some weld back in the 90s on one throw.  Designed for a 390, we had some big TRW slugs and had to make it up. Yesterday, a factory balanced 427 crank took a little  Mallory, with Diamond 4.25 with a slight dish, and SCAT H-beam, wasn't much but the rods are pretty heavy, which drove a small add.  Both of those were heavier components.  Hate to do it, but for the combo and budget was right.

Assuming your scenario of lower reciprocating and rotating weight dropped with new parts, I'd expect that any properly balanced crank would need drilling, not added weight as you describe. 

Haven't done a before and after with lighter parts on one that was already balanced though, but you have it right

ON EDIT: Brent is spot on with the target bob weight, I just did a 6-71 blown SBC with a lightweight internally balanced crank,  That crank came with documentation for the intended bobweight.  We couldn't get there with the combo we were using, although it was close, so it also took a little Mallory.  If I would have used a rod and piston combo that met the numbers, it likely would have balanced without weight.  Our "less expensive" FE cranks don't advertise a desired bobweight, but I did one with Molnar rods and a 17cc dish and it took very little Mallory, less than any I have seen before