Crankshaft balancing ?????

[parisherj]

Hey guys. I have a 82 chevy 350 4x4. Pretty much just a work truck. Haul wood, trash and my boat a few times a year. I'm rebuilding the motor and the crank was trashed. My question is with a new eagle stock crank do i need to have it balanced if i am using the stock rods and stock style pistons just .040 over. My old crank was already .010/.010 and the machine shop said it would be cheaper to get a new one vs fixing the old one. Thanks for any help on this.

[Engineer]

I would call Eagle and get their professional help.

They should have a tech line just for that purpose.

[Mario]

I had rebuilt 3 engines without balancing, and I thought they ran good until I built my last engine that was balanced.  It's like day and night.  A good engine machine shop will cut material off the heavy pistons and rods to get them weighing the same.  Then they'll spin the crankshaft with that much weight hanging on it, and take weight off the heavy side.  That may not be EXACTLY how it's done, but just in case you didn't know.  IMO, a balanced rotating assembly will run smoother, and smooth will last longer.  It may cost more, but I think you'll be happy with the result.

[SomeTexan]

I agree with you Mario. I balance my engines to within one grain. Takes forever to do, but pays off in the long run. Another thing to note, when I have ordered balanced eagle rotating assy, I had to balance it. Over an ounce out of balance. In other words, don't waste the money, just have a good local shop do it.

Something that will make your engine run smoother and last longer is a 4-7 swap cam. Swap the firing order and it takes care of most of the bad crank harmonics in an sbc. Although they are only advertised in higher end race cams, I know comp will make any cam you want in a 4-7 swap. I swapped out a extreme 4x4 cam for the same cam with a 4-7 swap and it was night and day difference. Ran smoother, and seemed a lot snappier.

[CipherLogic]

If you google "crankshaft balancing" the 3rd or 4th link down is Eagle's own website explaining this in great detail. Also make sure your machine shop has experience in this and is reputable. Eagle claims "cranks are made with enough bobweight that weight generally never needs to be added, only removed."

[Captkaos]

You need to have the rotating assembly balanced if you are replacing parts.  Even if you replaced pistons and reused the crank I would balance it.

[parisherj]

Thanks for all the replies guys. I talked to the shop doing the work on the block and he agreed it was cheap insurance. He's balancing it now. Thanks again guys.

[LeftysRodandCustom]

You dont have to balance it as most sbc's are externally balanced, but as has been said, its highly recommended. It's money well spent for durability and of course everybodys favorite, more power and quicker revs.

[SomeTexan]

Lets see, the 400sbc was external balance, but that is about it. Maybe some of the later model 350's, but I don't mess with them much. As I see it, most small blocks are internal balance. Even then, you should balance it. Part of balancing it is making sure everything weighs the same. One heavy piston/rod and your harmonics go to heck. Balancing is very important to a good engine build, without balancing, it's just a freshened up junkyard engine.

External balance just means some balancing is done outside of the block, ie weighted balancer and flywheel/flexplate. This in no way means an engine does not need to be balanced. It just means a shop will need your balancer and flywheel to balance it correctly. When I build 383's, I internally balance the crank and run neutral (internal balance) flywheel and balancer. 

Sorry there lefty, but external balance vs internal balance has nothing to do with if an engine needs to be balanced, just where the factory balancing was done. Not the kind of stuff I expect to hear from a rod and custom shop...

[HAULIN IT]

You dont have to balance it as most sbc's are externally balanced

Lefty, This is INCORRECT! The only sbc's that were externally balanced originally were the 400's. Since the 400 (3.75 stroke) cranks are often used in making a 383...many people leave them external as well. The O.P. stated he was working on a 350...none of those were externally balanced. Even externally balanced engines need the internal components weight matched & balancing done if parts are changed as the weighting externally was factored as a partial balance for the original items. "Externally balanced" engines are made because the engine block doesn't have enough room to house the crankshaft with counterweights large enough to offset the weight farther out from center from the long stroke...the crankshaft still has weight factored into the equation, but they needed more on the counterweight side so it's added externally to the damper & flexplate/flywheel instead of using expensive "heavy metal" like Mallory.    Hope this helps you understand, Lorne

[LeftysRodandCustom]

Yeah you guys are right here and I stand corrected. Texan, the name is merely a reference to my garage as my buddies will "check in" on facebook there lol, I do not run a shop at all. Home built hot rods only.

[SomeTexan]

Ok, I understand. Maybe I jumped a little, there was a bob's rod and customs down here for a while, took people's money then shut down and claimed bankruptcy. They re-opened and did it again, so a certain 260lb amateur mma fighter went and set the owner straight. Since then, I tend to avoid places with "rod and custom" in their title. The whole "one bad apple" thing...

[LeftysRodandCustom]

Yeah I completely understand ya there man. It all got started when i was building a rat and needed something for the door and just spiralled out of control from there. Good times with too many beers in the garage i suppose.

[thefarmboy21]

Just out of curiosity...for those of you that have balanced your engines, how much was the shop cost? Just trying to get an idea.

And do you weigh each piston/ring combo or just one out of the 8 going in? Thanks

[thirsty]

The last one that I had done was from PAW over 10 years ago. When I ordered parts it was an option to have the rotating assembly balanced and micro polished for about $125. Money well spent in my opinion.