Do I need to balance the crank?

Engine, Trans & Driveline

  1. BeepBeepRR

    BeepBeepRR FBBO Gold Member FBBO Gold Member

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    Couple ounces here, couple there.. whats the difference? Tell ya what go to a ceiling fan and tape a 1/2 inch nut to one blade and fire it up.. See what happens.
     
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    • 66 Sat

      66 Sat Well-Known Member

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      If your budget is tight wait a few more weeks and save the money up to get it done. It's cheap insurance. If it all goes back together and it has an imbalance you are stuffed, without a leg to stand on, as the machine shop has advised to have it done. The cost to pull the motor and then strip it all, and then pay to have it balanced will be considerably more (and way more hassle and stress). Do it once, do it right.
       
    • BSB67

      BSB67 FBBO Gold Member FBBO Gold Member

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      The wrist pins will weigh the same. The factory piston is 770 grams. If you're worried about it, put the TRWs on a scale. Unless something has changed in the world of replacement piston, they'll be close enough is my guess.
       
      Last edited: Dec 14, 2019
    • BSB67

      BSB67 FBBO Gold Member FBBO Gold Member

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      Cut the nut in half, and mount it 1 11/16" from the fan centerline.
       
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      • HT413

        HT413 Semi Pro Bowler

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        Here’s the advice my friend gave me: at 6000 rpm, each piston is changing direction 120 times a second...

        spend the hundred bucks
         
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        • BSB67

          BSB67 FBBO Gold Member FBBO Gold Member

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          Have your friend check his math. What else did he tell you?

          The changing direction of the piston has nothing to do with the need for balancing. Balanced or not the the 1000 gram piston/pin will be changing direction.
           
          Last edited: Dec 14, 2019
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          • 65-440

            65-440 Well-Known Member

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            Why risk it, it's not worth it to me. The engines already apart. Seems like a no brainier. How much are they charging you to balance?
             
          • 67charger383

            67charger383 Well-Known Member

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            Thanks to everyone who commented on this thread.

            I will have it balanced.
             
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            • BSB67

              BSB67 FBBO Gold Member FBBO Gold Member

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              Sure. Today, I would do it too considering my current situation.
              When I didn't do it, it was because there were a lot of other things competing for the $200, or what ever it cost back then.

              There were probably tens of thousands, if not a hundred thousand motors rebuilt without balancing through the 60's, 70's, 80's and early 90's before we got too smart to do such a thing. Just one more thing in the "you cant do that" bucket despite the fact that it used to be done all the time.
               
              Last edited: Dec 14, 2019
            • Curiousyellow71

              Curiousyellow71 Well-Known Member

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              Built many we did not balance. It would probably be fine. But it is cutting a corner...and I am glad to here you are balancing it. When they do the calculations for the bobweights for balancing the crank they use 100% of the rotating weight and 50% recipricating. The piston end accounts for 50% of the bobweight. So let's say your pistons are 50 grams heavier...it amounts to 25 grams on your bobweight. For most street builds it would be hard to tell the difference when your sitting behind the steering wheel. Some of the cheaper forged pistons are pretty heavy compared to the original cast piston...the only way to know is find the weights of both pistons and compare.
              I just wrote out a check to balance 2 mopars yesterday. 150 bucks per engine. Imo really reasonable. But I've paid $400 to have one balanced where Mallory metal had to be added...the new assembly had heavier rods and pistons then stock. Imo...its a common mistake buying rods and pistons. If you purchase lighter rods and pistons...they will have to lighten the crank which involves drilling holes in the counterbalances and is inexpensive. If you skimp and add heavier pistons or rods it's more expensive to balance if they have to add weight instead of drill. Some of the heavy metals are expensive. But...it all depends on how heavy or how light.
               
              Last edited: Dec 14, 2019
            • BSB67

              BSB67 FBBO Gold Member FBBO Gold Member

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              And I'd be surprised if a TRW/Speed Pro/Sealed Power replacement type piston would be 50 grams different than the factory piston.
               
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              • BSB67

                BSB67 FBBO Gold Member FBBO Gold Member

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                Actually, It's starting to come back to me. Those weights for the TRW/Sealed Power/Speed Pro pistons used to be published. I think the domed pistons were actually a little heavier, but they took weight out of the pin so that the balance would match the factory piston as well.
                 
              • Curiousyellow71

                Curiousyellow71 Well-Known Member

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                Yes... they tapered the inside ends of the wrist pin...and went from like 220g to 180g. Pretty trick set of pins back in the day.
                 
              • dvw

                dvw Well-Known Member

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                Tell ya what go to a ceiling fan and tape a 1/2 inch nut to one blade and fire it up.. See what happens.
                 
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                • Curiousyellow71

                  Curiousyellow71 Well-Known Member

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                  I would bet that there are more motors out there with trw/sealed power forged slugs that were not rebalanced then ones that were. That brand has been around forever and balancing used to be relatively uncommon...most machine shops would have to send it off to get the balancing done so balancing became a bragging point if you had it done..Lol. Like it was going to make it have another 100hp or something . Which I always thought was humorous and a sign someone didnt know anything....and they usually had a chevy. Lol.
                  Balancing has gotten more common in the last 20 years...a lot of shops can balance now and there doesn't seem to be as many machine shop around either. At least around here that is what I've seen.
                   
                  Last edited: Dec 14, 2019
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                  • 33 IMP

                    33 IMP Well-Known Member

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                    In theory, if the new piston weight is close enough to the old pistons, a rebalance shouldn't be necessary , BUT, why take a chance on losing fillings in your teeth if it did need a balance job? In the old days, when a rebuild was under a grand, I could see skipping a step here and there. Now that a fresh 440 is around five grand, what's another couple hundred bucks?
                    When I pulled my max apart, it had some unknown brand of domed forged piston in it, with a hard chromed crank. The piston weighed over a thousand grams,WITHOUT the pins and rings. The crank had four slabs of 1/4" steel welded to the crank cheeks. My new pistons weigh 750 grams with pins.
                    I think I'll rebalance.
                     
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                    • yella71

                      yella71 Well-Known Member

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                      Really? Comparing a ceiling fan to an engine? Good luck with your engine
                       
                    • threewood

                      threewood FBBO Gold Member FBBO Gold Member

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                      I'd say that while it's apart it is cheap insurance to have it done so it doesn't cost any sleepless nights. My engine balance cost $220 a few years ago.
                       
                    • dvw

                      dvw Well-Known Member

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                      Back in the day I was a dumb kid. My 1st car 68 Road Runner 4 speed. It had a transplanted 440, Cast iron 6 pac. Racing it at Milan Dragway, it lost about 15psi oil pressure. I could hear a ticking. Drove it home 45 miles. Puled the pan in my dads garage and found #5 rod spun. Crank looked fine. I pulled the head and piston/rod. Polished the crank with 400 grit. Then went to the dealer and ordered one new rod, $45 in 74. Who knew you could get used rods or have them resized? I didn't. When it showed up (10 days) it was much larger than the rest. In it went. Ran that motor for years after. Eventually I "rebuilt" it and put it in a Dart. By now I knew that it had one 6 pac rod and 7 LY rods. Swapped the one rod turned the crank, new rings, bearings, valve job.
                      Doug
                       
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                      • BSB67

                        BSB67 FBBO Gold Member FBBO Gold Member

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                        That's a funny story.
                         
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