[Mad Maggot]

I'm wondering if I purchase a Scat crank that is balanced and ready to go out of the box, and matched it up with close tolerance (+/- 1 gram) rods and equal weight pistons, if I need to get this assembly balanced. I know this is a costly procedure, and logic dictates that if all the pieces are already balanced, then there is no weight discrepancy from one part to another, so if this is the case, would it be prudent to skip the balancing? I plan on building another SBC 400 and I'm going to rev it around 6000-6200 RPM. I will get good quality forged parts, in case this is a concern.

[machine shop tom]

There is no such thing as a crank that is balanced and ready to go out of the box. The crank has to be balanced to YOUR particular parts combination. And rod sets and piston sets are rarely within a gram or so. I have checked more that a few "balanced assemblies" that were in need of a good balance job.

If you think that you can gather a bunch of parts that are close enough to not need balancing, think again.

tom

[coldknock]

Yep, in spite of the rods and pistons being matched sets, the crankshaft isn't balanced until the machine shop dude weighs them and actually does the job according to the bob-weight established with the pistons and rods you have.

No rough balancing job can account for all the different rod and piston weights. They have a "target" bob-weight that you can work toward when you purchase the rods and pistons but it still needs to be balanced.

Larry

[crazy larry]

if you've spent the money on a new crank, it would be most prudent to have it balanced. money well spent.

[Mad Maggot]

D'OH!!!!!!!!!!

That adds like $700 to the cost of my engine... CH-CHING!!!

I guess if it is necessary I won't cheap out.

[baddbob]

Most shop's I've delt with charge about $200 to balance an assembly, I usually weight match the pistons and rods before taking them to the machine shop-saves them a little time.

[cliff tate]

ballance job hear in surrey bc is 250 that is canadian if you want a phone no mad magot send me a email. frt to and from cant be much. cliff ct1940@telus.net. to not ballance with your investment insane.

[k-star]

I am not sure if you are getting confused about what a target bob weight is???

Many crank makers will list a target bob weight for the crank. But as Tom and other have stated even if you get your assembly to this target weight it is not even close when you spin the crank.....

So for your answer Yes you need to balance it,,,, no you don't need to pay $700 to get the job done!!!!