A few weeks back, we picked up a 427 shortblock for a build up to go into a 69 Chevelle SS. It consists of a 454 4 bolt block, 396 forged crank, stock rods with Milodon rod bolts, and TRW dome'd 427 pistons.

From looking at the rods, they were balanced, and the crank has 3 or 4 holes drilled in each counterweight. There is no metal added.

I know the 396/427 is internally balanced while the 454 is externally balanced. Is it possible to remove weight from the stock 396 crank and make it externally balanced? I'm trying to find out if I need to pick up a 396/427 or 454 flywheel and damper.

Thanks guys
Nick

you shouldn't need externally balanced stuff for a 396/427 unless some previous owner did something really dumb. However, a mix-n-match combo like that should be balanced. No question about that.

Well I believe this rotating assembly was balanced, I just don't know if it was internally balanced or externally balanced.

Normally, how many holes are drilled in each counterweight on a stock forged 396 crank? With the amount that are there now and the heavier than stock pistons, I'm thinking instead of adding weight to keep it internally balanced, they removed weight and used externally balanced flywheel/balancer.

I know to check the balance, the pistons will need to be R&R'd from the rods, everything weighed, and than any changes done from there. I'm trying to keep this build simple and on budget.

Thanks for your input.

Nick

what i've seen done typically on this type of assembly was that they added some weld into the balance holes on the 396/402 crank. the pistons are not too much heavier depending on the manufacturer and model of piston. your new pistons could have been close to the 396-piston weight and no changes were needed.

you can also use the flywheel for a 350sb on this engine, internal balance also...... :)

This engine will be replacing a 396...I'm hoping we can use that flywheel if it is indeed internally balanced, and then we can just pick up a standard internally balanced damper. Since we will be breaking this motor in on a run stand, I guess we could try running the 396 flyhweel/damper. If doesn't rattle itself, we are good to go.

The 'right' way to do it would be to have everything weighed and balanced (if necessary). If that's not in the budget, I'd use a neutral balance damper and flexplate.

I bought a forged crank to build a 402 for my car. I took it and all the rotating parts to the machine shop to be balanced. When I picked up the parts he told me he had to take 94 grams out of the front counter balance and a little over 100 out of the other side. He said his guess was it was set up as a truck crank, there pistons have one more ring and are heavier. I don't know if it's true or not but he said, your good to go. It was a 6223 crank. here is a pic of one side.



http://i173.photobucket.com/albums/w56/flattop56/machiningpistons013.jpg

Hmm that looks similar. Maybe it was a truck crank, I believe this motor does have a 6223 crank also. I gotta look at it closer.

Thanks guys.

Nick,
Take a good look at the counterweights and see if there are any numbers stamped into them. Just about everyone that I knows that does balancing stamps or engraves a job number somwhere on the crank for future reference. If you find a number, maybe someone local to you that does balancing will "recognize" it. I always stamp mine with "AA" and the balance card number.

Definitely something I'll look for. Thanks for the heads up.

there's no reason to assume the thing is externally balanced. Can't think of any reason anybody would do that.

MANY home brew 427s are made from 454 blocks and 396/402/427 cranks.....
they will be internally balanced because the small stroke 3.76 crank is internal balance.
External balance of this would be a tail-chasing expedition of stupendous magnitude.
End of story.
Use the 396 balancer and flywheel if they are in good shape....

My 427 in the gallery is forged 427 guts in a 454 4-bolt block:cool: