Can You Put Slightly Lighter Pistons in a 440 Mopar and Not Balance It

1. 

   drobertson Well-Known Member

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   And then I'm gonna build a 440 soon. It's a 74' cake bored .forty 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 become a harmonic balancer and flexplate from them as well, depending on whether the crank I become happens to be a cast or forged one. I will be using the stock LY rods, with ARP bolts. Hither is the real question... When choosing pistons, how important is information technology that I take the rotating assembly professionally balanced? I'm using a factory crank and rods, and then tin can I just throw in some kb pistons and phone call information technology good https://www.summitracing.com/parts/uem-kb237-040/overview/make/dodge? I will exist using the proper flexplate and balancer for the crankshaft. This engine volition be in a 73 Charger, driven mostly on the streets, and occasionally at the local airport drag races. Thanks. -David.

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

   • Thanks! x i

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

4. My opinion, if you build a new motor, do the balance. Pistons, pins & crank are non however.

5. 

   IQ52 Well-Known Member

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   Here is the plan. Put it together unbalanced with what ever parts yous want. When information technology vibrates, start another thread asking why your unbalanced engine vibrates. Nosotros tin can tell you it is considering you didn't balance your engine. And so yous can tear information technology downwards and have it balanced.

6. Ouch!..... but to the point. I ran one un-balanced 383 fashion-dorsum-when, simply I had 100% stock parts... pistons, rods, rod bolts, creepo, balancer, flywheel.....100% stock parts.

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   727 Well-Known Member

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   KB pistons are much lighter than stock pistons. Your engine volition shake. Whichever crank yous get, make certain to use the correct hermonic balancer and if it's a cast crank, utilize a residuum wieghted torque converter. Bring every part of the rotating associates including balancer, flex plate, and converter to the the automobile shop when getting information technology done

8. Ha! Yeah, me too!
   Done a handful of 383s, never a 'vibration problem', even using lighter weight after market piston/pin sets. Only, that's the key word...set...all weighing the same. Fully concur if they don't weigh the same, or yous mix and match rods, needs to be counterbalanced. 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 bound up. I've fifty-fifty balanced/blueprinted i motor...couldn't tell whatsoever dif.
   Balance away...your the one picking your parts! Book specs tell the stock piston weight. Bottom line is the parts used need to friction match, even if lighter, as in aluminum rods!

9. But do information technology!...whats another 150$ when your building a Mopar?

10. Please balance information technology then you don't have to cry too us subsequently. also bring your crank caster and brand sure y'all index everything even the creepo sprocket. if you past a kit from Hawkeye or the other crank companies they will do entire assembly for a few bucks more.

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Source: https://www.forbbodiesonly.com/moparforum/threads/440-balancing-how-accurate-does-it-need-to-be.116176/

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