440 balancing... how accurate does it need to be

[drobertson]

So I'm gonna build a 440 soon. It's a 74' block bored .40 over. The bores are actually pretty good, so I'll probably just hone the block. I'm gonna get a new crankshaft from napa, and get a harmonic balancer and flexplate from them as well, depending on whether the crank I get happens to be a cast or forged one. I will be using the stock LY rods, with ARP bolts. Here is the real question... When choosing pistons, how important is it that I have the rotating assembly professionally balanced? I'm using a factory crank and rods, so can I just throw in some kb pistons and call it good https://www.summitracing.com/parts/uem-kb237-040/overview/make/dodge? I will be using the proper flexplate and balancer for the crankshaft. This engine will be in a 73 Charger, driven mostly on the streets, and occasionally at the local airport drag races. Thanks. -David.

 

[miller]

Not really, unless a full blown race motor. Balancing is nice to have, but as on pistons, as long as they are out of the same box, as a set, pretty well matched for running specs.

 

[PurpleBeeper]

I would disagree. If you don't have at least a factory balance on the engine, you will beat the bearings right out of the motor. Balancing is +/- 1gram or +/- 2grams on piston/rod weight I believe (on both ends). Anyway.....In my opinion, the only way to feel comfortable without balancing the engine is to use 100% stock/matched parts OR if the pistons are not stock, make sure they're +/- 2 grams of the OEM piston weight. The engine balance is not only between pistons/rods, it also involves the crankshaft counterweights. If I were you, I "might" consider ignoring the weight difference of the ARP rod bolts, but I would never ignor the piston weight. IMO opinion, find pistons that are stock weight or balance the engine.

 

[66Satellite47]

My opinion, if you build a new motor, do the balance. Pistons, pins & crank are not all the same.

 

[IQ52]

Here is the plan. Put it together unbalanced with what ever parts you want. When it vibrates, start another thread asking why your unbalanced engine vibrates. We can tell you it is because you didn't balance your engine. Then you can tear it down and have it balanced.

 

[PurpleBeeper]

Here is the plan. Put it together unbalanced with what ever parts you want. When it vibrates, start another thread asking why your unbalanced engine vibrates. We can tell you it is because you didn't balance your engine. Then you can tear it down and have it balanced.

Ouch!..... but to the point. I ran one un-balanced 383 way-back-when, but I had 100% stock parts... pistons, rods, rod bolts, crank, balancer, flywheel.....100% stock parts.

 

[727]

KB pistons are much lighter than stock pistons. Your engine will shake. Whichever crank you get, make sure to use the correct hermonic balancer and if it's a cast crank, use a balance wieghted torque converter. Bring every part of the rotating assembly including balancer, flex plate, and converter to the the machine shop when getting it done

 

[miller]

Ouch!..... but to the point.

Ha! Yeah, me too!
Done a handful of 383s, never a 'vibration problem', even using lighter weight after market piston/pin sets. But, that's the key word...set...all weighing the same. Fully agree if they don't weigh the same, or you mix and match rods, needs to be balanced. Though, if your using the original 'set' of matched rods out of the motor, should be within reason. Mixing and matching parts of your rotating stock is where problems can jump up. I've even balanced/blueprinted one motor...couldn't tell any dif.
Balance away...your the one picking your parts! Book specs tell the stock piston weight. Bottom line is the parts used need to match, even if lighter, as in aluminum rods!

 

[mentor70]

Just do it!...whats another 150$ when your building a Mopar?

 

[snakeoil24]

Please balance it so you don't have to cry too us later. also bring your crank pulley and make sure you index everything even the crank sprocket. if you by a kit from Eagle or the other crank companies they will do entire assembly for a few bucks more.