# Crankshaft balancing



## 68_Tempest (10 mo ago)

Hi,I have been collecting parts over the winter to rebuild a 400,I bought new eagle rods &Speed pro pistons since the pistons are supposed to be near the same weight but the rods are 870 vs factory 900 grams I'm wondering which way is the easiest to balance it,stock external or internal balance?


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## PontiacJim (Dec 29, 2012)

68_Tempest said:


> Hi,I have been collecting parts over the winter to rebuild a 400,I bought new eagle rods &Speed pro pistons since the pistons are supposed to be near the same weight but the rods are 870 vs factory 900 grams I'm wondering which way is the easiest to balance it,stock external or internal balance?


Internal is best (neutral balance), but can cost more if the crank needs to have "heavy metal" (mallory) added to it or the crank journals drilled.

External can be more affordable. Pistons/pins/ring set, rods/bearings, harmonic balancer, and flywheel/flex plate. Typically about $250.00, but with the price of a barrel of oil going up, don't be surprised if your machine shop uses this to jack up the price on you like everyone else in the country.


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## 68_Tempest (10 mo ago)

Im wondering how it will balanced as a external setup? Do they simply drill it? I'd prefer to stay away from the Mallory metal if at possible, thanks


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## geeteeohguy (Feb 2, 2008)

Have had many engines balanced and none of them needed added metal. All had some drilling/grinding/polishing. Have seen engines that metal had been added to, but none were personally mine. The likelihood of additional metal being needed on a factory Pontiac crank is not high, IMO.


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## 68_Tempest (10 mo ago)

geeteeohguy said:


> Have had many engines balanced and none of them needed added metal. All had some drilling/grinding/polishing. Have seen engines that metal had been added to, but none were personally mine. The likelihood of additional metal being needed on a factory Pontiac crank is not high, IMO.


So in your opinion it's best to stay with the factory external balance flex plate? Thanks,


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## PontiacJim (Dec 29, 2012)

68_Tempest said:


> So in your opinion it's best to stay with the factory external balance flex plate? Thanks,


Yes, you can use it, BUT, it needs to be included when you bring all your parts to the machine shop/engine builder for balancing as I posted earlier. If you assemble the rotating assembly with the new rods/pistons, don't assume you will have a balanced assembly. Any time you make changes to the rotating assembly, such as new rods/pistons, you want to have it balanced.

The shop who balances the parts will make adjustments as needed which can include balancing all the pistons to match the lightest one, balancing the rods to match the lightest one, and then balance the assembly as a unit. He may or may not have to drill a few holes here and there to remove metal for balancing when externally balancing the assembly. They can even add weights to the flex plate as a means to balance the assembly. So cheaper to go external than internal on the balance.

Now TRW pistons were said to be factory replacements so no balancing was needed, but they had lighter forged pistons and heavier pins to weigh the same as the factory cast piston/pin so it did not upset balance.

So it is your call if you want to chance it and assemble the engine and hope you don't get any vibrations or not. Vibrations will damage bearings and eventually the engine. Talk to the machine shop you are considering doing the job and see what he requires of you and quote a price.


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## 68_Tempest (10 mo ago)

PontiacJim said:


> Yes, you can use it, BUT, it needs to be included when you bring all your parts to the machine shop/engine builder for balancing as I posted earlier. If you assemble the rotating assembly with the new rods/pistons, don't assume you will have a balanced assembly. Any time you make changes to the rotating assembly, such as new rods/pistons, you want to have it balanced.
> 
> The shop who balances the parts will make adjustments as needed which can include balancing all the pistons to match the lightest one, balancing the rods to match the lightest one, and then balance the assembly as a unit. He may or may not have to drill a few holes here and there to remove metal for balancing when externally balancing the assembly. They can even add weights to the flex plate as a means to balance the assembly. So cheaper to go external than internal on the balance.
> 
> ...


Thanks Jim, i had planned on bringing in the harmonic balancer and flex plate in with my rods&crank,pistons, pins etc,I chose speed pro pistons rather than icons in hopes in having a 90k mile motor and balancing it correctly will help achieve that goal


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## PontiacJim (Dec 29, 2012)

68_Tempest said:


> Thanks Jim, i had planned on bringing in the harmonic balancer and flex plate in with my rods&crank,pistons, pins etc,I chose speed pro pistons rather than icons in hopes in having a 90k mile motor and balancing it correctly will help achieve that goal



OK, great. Just would have hated to see you "wing it" and then fire the engine up and feel a bad vibration.

When I rebuilt my '72 junk yard engine, someone had installed the late model small balancing hub. I did not think too much about it and I used all stock parts to include replacement cast pistons so I did not have to balance the rotating assembly. The engine always has a slight vibration, but not annoying or really bad, but I could feel it so I just figured it was that "hot" Comp Cams XE274 cam that gave it that vibration, right? But I learned later through one of the Pontiac engine assembly books that Pontiac used a hub, not a balancer, on the later engine because they were low HP and to save money. So when I pulled the engine and began to disassemble it, I knew where my vibration was coming from. LOL

Here is what a solid hub looks like.


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## 68_Tempest (10 mo ago)

Thanks for the info,your name popped quite a bit while googling info on Pontiacs,so I know your a been there done that Pontiac mechanic 👍


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## lust4speed (Jul 5, 2019)

Every shop I've used charges the same for external/internal balancing processes. Agree with Geeteeohguy that the stock cranks come back with additional metal removed from the counterweights, and never had the need to add any heavy metal. Those original parts were heavy. Final product ends up just as smooth either balance as long as the guy doing the balancing is doing his job.


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## Old Man Taylor (May 9, 2011)

The advantage of the internal balance is that you can interchange flywheels/torque convertors with no problem - just make sure they are "zero" balanced.


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