Explain this GM 602/604 Crank Balancing numbers

[Bos's5.0]

I'm curious if anyone could explain to me what is going on here with these balancing numbers as instructed by GM on their sealed race 602/604 engines. I'm not an engine builder or professional, but these are weird.

IMG_20211103_115632302.jpg

[mag2555]

Real good question!

Since 3 out of the 4 pin ends listed veri a lot in weight then one would have to assume that 3 different types of pins and or rod type ends could have possibly been used in those two motors in your question.

I don't know if these motors when done in normal GM production line fashion, by if so then the final balance was done by spinning the assembled short block up with the heads still off.

If they did it that way then they could at that point make up for the weight difference.

If you look in a GM parts book and find different part number listings for Rods and or pins for these two motors then that might explain it.

[Dave Koehler]

While the end result works out something is going on there relative to position.
Center 2 are identical.
Front is heavier than the rear
Averaging the weights out ,the first one is the lightest assembly and the last 2 are the heaviest assemblies FWIW.

It might help to see the cranks side by side. Also wondering what is hanging off the front and rear of the engine. Does that play a part?

It will be nice to figure this out.
The last thing I need is another trick balance job being requested by internet crew chiefs.

[dannobee]

One crank (12556307) is forged steel crank with 2.1 rod and 2.45 mains
One crank (10243068) is cast iron with 2.0 rods and 2.65 mains
One crank (14088526) is cast iron with 2.1 rods and 2.45 mains.

[strokersix]

Bobweights to balance an external balance crank without damper and flywheel perhaps?

[miniv8]

I think this is the best crank balancing, piston/rod weight thread there is.

Everyone is ReBalancing for three grams...
General Motors... Hold my beer!

[Dave Koehler]

Bobweights to balance an external balance crank without damper and flywheel perhaps?

1: If that were the case the end journal numbers would be greater than the middle two....in a normal scenario.
2: Since it appears to be deliberate I wonder if they are trying to counter some crank flex. How is that for far out?
3: I am upset that they would publish that without some explanation.
4: It's pretty much impossible to acquire a replacement rod or piston 3 yrs later that comes close to the original part weight.
This will be a nightmare.
5: I really hate engineers raised on common core math.

[Bos's5.0]

One thing I forgot is on these vortec motors, the flexplate has a small weight on it. This is standard issue.

I've never seen personally or heard of balancing where you have 3 different weights hanging off your crankshaft and I can't imagine this is the mathematics for balancing the assembly without the balancer and vortec flexplate.. that would be insane

[Dave Koehler]

One thing I forgot is on these vortec motors, the flexplate has a small weight on it. This is standard issue.

I've never seen personally or heard of balancing where you have 3 different weights hanging off your crankshaft and I can't imagine this is the mathematics for balancing the assembly without the balancer and vortec flexplate.. that would be insane

Do you know if these are internal or external assemblies?

[Bos's5.0]

One thing I forgot is on these vortec motors, the flexplate has a small weight on it. This is standard issue.

I've never seen personally or heard of balancing where you have 3 different weights hanging off your crankshaft and I can't imagine this is the mathematics for balancing the assembly without the balancer and vortec flexplate.. that would be insane

Do you know if these are internal or external assemblies?

I know the vortec flexplate looks like this.
https://www.jegs.com/i/Chevrolet-Perfor ... 1/10002/-1
8" balancer but I'm still searching for the part no.

[Elroy]

10243068 is also 2.45 main 2.10 rod. Production L31 crankshaft.

[strokersix]

1: If that were the case the end journal numbers would be greater than the middle two....in a normal scenario.

I'm not sure about that.

My understanding. The point of external balance is because there wasn't room to make the crank counterweights big enough. I have never balanced a crankshaft so below may be all wrong:

Bobweight is opposite the crank counterweight. External balance is aligned with counterweight. Missing external balance weight effectively means a smaller counterweight. Then you need less bobweight opposite the smaller counterweight to balance the crank without damper and flywheel.

Logical explanation but like I said, could be all wrong. Correction welcome.

[BillK]

That is totally odd The specs say it needs an external balance flywheel. I would love to see the rest of the tech documents. Or as Paul Harvey used to say "The rest of the story"

https://static.speedwaymotors.com/pdf/19258602.pdf

https://www.speedwaymotors.com/Chevrole ... 67820.html

[Dave Koehler]

More alien common core math mysteries.
Why is a 350 called a 602?

[Bos's5.0]

1: If that were the case the end journal numbers would be greater than the middle two....in a normal scenario.

I'm not sure about that.

My understanding. The point of external balance is because there wasn't room to make the crank counterweights big enough. I have never balanced a crankshaft so below may be all wrong:

Bobweight is opposite the crank counterweight. External balance is aligned with counterweight. Missing external balance weight effectively means a smaller counterweight. Then you need less bobweight opposite the smaller counterweight to balance the crank without damper and flywheel.

Logical explanation but like I said, could be all wrong. Correction welcome.

Nobody balances a crank like that. You get your ONE bobweight from the parts you have, install the flywheel/flexplate and the dampner on the front and see how far off the balance is, and go from there. YOu either add weight to the crank, or take it off. There is NO 3 bobweight system.