Balancing a Scat cast crank

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The Eagle forged 434040006123 forged crank has a bobweight of 2050g, The SCAT being 1700g (!) is begging for tungsten!! I'd rather take weight off than add when it comes to a crankshaft and the price of heavy tungsten slugs. Cast cranks are lighter than Forged....sort of apples to oranges there.
 
I'm about to build the strategy to correct the unbalance WITHOUT removing the engine and start the engine build from the start :). One option is to move to external balance solution and add weight to the balancer and to the flywheel/converter, still to be decided and still to be executed :)
 
mini said:
Yeup CNC motorsports balanced my assembly with Mallory.
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:) I'm looking for some experiene when it comes to moving from a badly internal balanced 408 stroker to a corrected good balance external balanced engine with just added wights to the balanser and the flywheel. /Morten - Norway
 
My scat cast crank, with the scat I beam rods and Icon FHR pistons needed two slugs up front, and one out back. That's with a bobweight of 1770. If you're running stock rods and/or heavy pistons it can be a good bit higher.
 
Morten Stroem said:
:) I'm looking for some experiene when it comes to moving from a badly internal balanced 408 stroker to a corrected good balance external balanced engine with just added wights to the balanser and the flywheel. /Morten - Norway
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You can't do what you're asking. If the rotating assembly is out of balance, just adding weight on the front and rear by using an external balance damper and tq converter won't work.

You have some residual unbalance, obviously enough that you're feeling it in the car. The issue is you don't know how much, or the exact angle, of that unbalance. When you put the external balance parts on, you're adding weight of a specific amount, and at a specific angle, which aren't necessarily where you need the extra weight.

Engine needs to come out, crank needs to go back, and be rebalanced with the external damper/converter.
 
I can't see doing internal balancing with a cast crank...just doesn't seem cost effective.

For what its worth, my Scat forged crank, forged Icon flat tops & Scat I-beams did not need any heavy metal for balancing.
 
20141215_132248.jpg

Mine...
 
I'm about to build the strategy to correct the unbalance
I have an internal balanced 408 stroker setup


Balanced ................................................Internal balanced, balanced assembly
Connection Rods ....................................Chrysler Rod 6.123[/QUOTE]
I'm not so clear as to how or what you have going on! If you had a shop balance it, and even ran it on a dyno, Why does the balance job need to be fixed? Do you have something else out of weight? As in the flex plate or torque convertor? OR, was it never actually balanced. Who assembled it? Was there malaroy metal added to the cast crank, it would have been obvious.
 
TurboGLH said:
You can't do what you're asking. If the rotating assembly is out of balance, just adding weight on the front and rear by using an external balance damper and tq converter won't work.

You have some residual unbalance, obviously enough that you're feeling it in the car. The issue is you don't know how much, or the exact angle, of that unbalance. When you put the external balance parts on, you're adding weight of a specific amount, and at a specific angle, which aren't necessarily where you need the extra weight.

Engine needs to come out, crank needs to go back, and be rebalanced with the external damper/converter.
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Good thinking :) tnks
 
cast cranks are lighter by the manufacturing process. they are less dense than a forged (compressed) crank so your going to have to add weight to the throws to compensate for 1-heavier bobweight of rods and pistons or 2. lighter balance throws to begin with. I think your fighting 2, lighter throws. Tungsten is going to have to be added to the throws to make the bobweight compensation heavier. They had to use external balancing on cast crank 360 and 340 motors because the cranks were lighter by about 5 lbs with all other parts being the same as the forged crank motors so they had to add weight where they could externally, the balancer and the convertor or flywheel. I dont see an issue making it an external, you just have to supply and weighted 360 B&M flex plate and a cast 340/360 balancer, then weight can be taken from these parts. Anything can be internally balanced but at a cost of mallory metal/tungsten.
normal_internalbalance.jpg

If your going to start the balancing act, supply a weighted (cast 340 or 360) balancer to begin with. cheaper that tungsten.
 
pishta said:
cast cranks are lighter by the manufacturing process. they are less dense than a forged (compressed) crank so your going to have to add weight to the throws to compensate for 1-heavier bobweight of rods and pistons or 2. lighter balance throws to begin with. I think your fighting 2, lighter throws. Tungsten is going to have to be added to the throws to make the bobweight compensation heavier. They had to use external balancing on cast crank 360 and 340 motors because the cranks were lighter by about 5 lbs with all other parts being the same as the forged crank motors so they had to add weight where they could externally, the balancer and the convertor or flywheel. I dont see an issue making it an external, you just have to supply and weighted 360 B&M flex plate and a cast 340/360 balancer, then weight can be taken from these parts. Anything can be internally balanced but at a cost of mallory metal/tungsten.
View attachment 1715573250
If your going to start the balancing act, supply a weighted (cast 340 or 360) balancer to begin with. cheaper that tungsten.
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Tnks Pishta :)
 
Max1196 said:
I'm about to build the strategy to correct the unbalance
I have an internal balanced 408 stroker setup


Balanced ................................................Internal balanced, balanced assembly
Connection Rods ....................................Chrysler Rod 6.123
Click to expand...
I'm not so clear as to how or what you have going on! If you had a shop balance it, and even ran it on a dyno, Why does the balance job need to be fixed? Do you have something else out of weight? As in the flex plate or torque convertor? OR, was it never actually balanced. Who assembled it? Was there malaroy metal added to the cast crank, it would have been obvious.[/QUOTE]

This 408 stroker Mopar engine was purchased ready build and the history of balanced or not, will be unknown for all future
 
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I built a 416 a few years ago.
Scat 9000 crank, Scat I beams, ProTrue pistons.
It balanced internally without heavy metal.

I supplied the same part number crank and rods to another customer this spring, along with Icon pistons.
Needed heavy metal for internal balance.

For the next one I used a Molnar steel crank and h beam rods, same # Icon pistons.
Had to take a bunch of weight out to balance it.
 
so these 408 kits that are sold as balanced kits, need balancing ? I have been looking at the Scat 360/408 kits and some are sold balanced and some not balanced, so if the kit is going to need balancing why spend extra money on a kit that is balanced.
 
RedB. said:
so these 408 kits that are sold as balanced kits, need balancing ? I have been looking at the Scat 360/408 kits and some are sold balanced and some not balanced, so if the kit is going to need balancing why spend extra money on a kit that is balanced.
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You don't need to balance the kits sold as balanced. Some people prefer to have stuff balanced locally, and some people are ok with having scat balance them.
 
RedB. said:
so these 408 kits that are sold as balanced kits, need balancing ? I have been looking at the Scat 360/408 kits and some are sold balanced and some not balanced, so if the kit is going to need balancing why spend extra money on a kit that is balanced.
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They come either balanced or not. Balanced is usually a $200-$300 adder
 
My machinist told me when he has checked those that are SCAT balanced, they are not as well balanced as he likes. Course maybe he likes doing the work to pay for his machine.
Just an FYI, the flywheel for external balance is on the spendy side.
 
Idaho said:
My machinist told me when he has checked those that are SCAT balanced, they are not as well balanced as he likes. Course maybe he likes doing the work to pay for his machine.
Just an FYI, the flywheel for external balance is on the spendy side.
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True. I don't have a problem with local machine shops paying for their balancing equipment.
 
Would a flywheel or flex plate, or harmonic balancer from a internal balance 340 318 work on these Scat internal balance cast crank 360/408 ?
 
would depend on your bob weight
if heavier rod and piston the 360 parts save on balancing
get your numbers together and ask your balancer or post back
if tour question was if the rotating assembly is already balanced internally then yes 318 will work or forged crank 340
 
All this balancing talk has reminded me I need to check some piston weights before I screw my fresh race motor together...new pistons new weight.
 
I have now run that crank externally balanced for over 1000 runs and a bunch of street miles. 55,000+. No issues, changed pistons a couple a years ago and had it balanced again externally. The REALLY old, REALLY smart guy who did it is kind of a perfectionist. IIRC Got it to within 1/2 a gram. Way closer than it really needed. Shift it at 6400 rpm.
 
flyfish said:
I can't see doing internal balancing with a cast crank...just doesn't seem cost effective.

For what its worth, my Scat forged crank, forged Icon flat tops & Scat I-beams did not need any heavy metal for balancing.
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Can you use forged flattop pistons, H rods, and CAST crank with a 3.58" throw in a 340 block....and get away without balanceing anything, DONT want to pay if it's in the ball park. Would it be considered internal or external balance?
 
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