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Old 06-04-2008, 07:07 PM
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Flex Plate - Internal or External balanced

Guys - I'm trying to determine the right flex plate to order for my little street truck.

Engine is a 77-79 GM Goodwrench Crate Engine... pretty much stock.

How do I tell if it is internal or external balanced.... i.e., which flex plate that I need?

The block casting # is #14016379 if that helps.

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Old 06-04-2008, 07:12 PM
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As far as I know...all sbc's except the 400 are internally balanced.

Last edited by Henry Highrise; 06-04-2008 at 07:18 PM.
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Old 06-04-2008, 07:15 PM
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Really? According to the application stuff at summit and jegs, they say internal applies too.

It is a GM 350 SB, forgot to mention that.
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Old 06-04-2008, 07:19 PM
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My bad...senior moment...The 350 is internally balanced.
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Old 06-04-2008, 07:23 PM
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How sure are you? If so, that would indicate I need an internal balance flex plate?

Anyone else care to weigh in and confirm?

Many thanks
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Old 06-04-2008, 07:25 PM
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I used the search function on this site...keyed in external internal balance....it brought up a lot of info to verify it. Here is one thread on this subject. Check it out... Balancing Question
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Old 06-04-2008, 07:28 PM
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Yes...you need a internal balance flexplate and also a internal balance harmonic balancer ( damper).
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Old 06-04-2008, 10:03 PM
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Quote:
Originally Posted by Henry Highrise
As far as I know...all sbc's except the 400 are internally balanced.
all sbc are not balanced from the factory, they all come heavy What I mean is the cranks are all heavy because if you want it balanced the weight is there to come off. Also you want a external balanced flex plate. If something should happen to the flex plate and it is internally balanced you would have to disassemble the engine to rebalance the rotating assembly.
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Old 06-04-2008, 10:11 PM
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So how do i tell? I'm really perplexed? Its just a stock replacement 350 crate enginge from 1977-1979. I had planned to use the damper that was on it in the big truck it came out of, but just convert to a 700R transmission.

What are the noticeable differences in an external versus internal balance flex plate?
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Old 06-05-2008, 07:08 AM
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Flexplates for early 350's (gen 1) don't come internal/external balanced. The flexplate is just balanced to itself. Some people will balance a crankshaft with the flexplate attached and compensate by adding or subtracting weight to the crank but if your motor is a stock crate motor and you never took it apart to have it balanced than you'll be ok. The bigger question is whether a flexplate for a 700r4 tranny will even bolt up to an early 2-piece rear main engine like you have.
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Old 06-05-2008, 09:56 AM
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Quote:
Originally Posted by Blacktop Motorsports
Also you want a external balanced flex plate. If something should happen to the flex plate and it is internally balanced you would have to disassemble the engine to rebalance the rotating assembly.

I believe you have it backwards here. If the motor is internally balanced you want an internally balanced flexplate and dampner because they are "zero" balanced. Then if you want to change the flexplate to a flywheel or change the size of the dampner you just need to get ones that are "zero" balanced as well.

Internal balancing is the way to go for flexiblity when it comes to the flexplate and dampner. You can usually buy a new flexplate or dampner and bolt it on if it is neutral. It is always a good idea to have it checked before installation though.

so if you have an externally balanced motor you will need to have the new parts balanced the same way as the old ones and if you have lost your balance card then you will have to take the entire motor apart and have the whole thing redone.
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Old 06-05-2008, 10:04 AM
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Quote:
Originally Posted by dhunt00c

What are the noticeable differences in an external versus internal balance flex plate?

The external balancer will have large area's removed from the sides of the damper in different areas. The internal balancers will be a nice cylinder that is solid all the way around and just have a few holes drilled in it to remove some weight.

The external flexplate will have a large weight welded to it in one spot usually on the inside (towards the motor)

The only ones that have external balancers are the 400's or 383's that are based on a 400 crank.

Your 350 is definately internally balanced, but as stated before is probably not perfect from the factory...however just find a neutral balanced (internal) flexplate with a dual pattern for the torque converter bolts and you will not have a problem.

Here is a cheap one that will work...http://www.competitionproducts.com/p...?number=FRA100

here is a Good one that is SFI rated at a reasonable price

http://www.competitionproducts.com/p...ber=PRW1835001

Just make sure you figure out how many teeth yours has right now.

Last edited by Double_v23; 06-05-2008 at 10:14 AM.
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Old 06-05-2008, 03:46 PM
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Quote:
Originally Posted by dhunt00c
Guys - I'm trying to determine the right flex plate to order for my little street truck.

Engine is a 77-79 GM Goodwrench Crate Engine... pretty much stock.

How do I tell if it is internal or external balanced.... i.e., which flex plate that I need?

The block casting # is #14016379 if that helps.
This is a two piece seal 350, they are all internally balanced and use a zero or neutral balanced flywheel or flexplate, and damper.

Bogie
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