Huh?

Every 1-piece rear seal engine is externally balanced on the flywheel from the factory with the same weight.

Every 2-piece rear seal crank from the factory has an irregularly shaped flange behind the seal that has a heavy side, which of course acts as a balance weight because it's not round and even.

Every 2-piece rear seal 400ci engine is externally balanced on the flywheel from the factory with the same weight.

IF you are balancing a 383 2-piece or 1-piece with an externally balanced flywheel then you use the stock weight. You don't use some other weight. As long as you buy a properly built flywheel with the stock weight it will work.

Manufacturers make flywheels that duplicate the factory weight for both the 1-piece and 2-piece rear seal engines. They also make neutral balanced flywheels for both. All you need to know on a built engine is if you should use a neutral balanced or weighted flywheel.

The above is nothing new, it's the way it has always been.

 

Also,. if done right, the shop will confirm the customer supplied flywheel matches the factory balance. They should not just bolt it to the crank and balance the whole mess together. If they do that then there is the risk that the customer can't simply replace the flywheel with another one and still maintain the engine balance. Same applies to the damper.

 

You are not following at all.
A 2 piece rear main seal 383 external crank has about 70 more ounces of weight out near the gear slinging around. The weight on a 1 piece seal crank is strictly there to compensate for the round crank hub. You yourself said that there is a weightless 1 piece seal flywheel and there is....but not from the factory. So, the added weight is in the rear counterweight. And it is important to have the correct flywheel. This is all I am saying. What baffles me is that if they (Scat/Eagle) are able to compensate for 70/80 oz. of weight that is missing in the 1 piece setup....why don't they change the counterweight on the 2 piece as well so you can just run a neutral flywheel/flexplate?
There are many who balance external stuff to their "shop" flywheel and damper......the Pro's do not and will not. In fact, many won't even balance an external period. Eagle and Scat quit doing it due to returns...they include the flexplate it was spun with and in some cases the damper. You want to gamble....fine, but I will not. Even as far back as the 90's.....if a customer jacked up a flywheel on one of these external assemblies...the new one would be sent with the old one to confirm it. I have seen brand new Pioneer flywheels that have to be drilled to match an existing assembly. It is just good practice and attention to detail.

Jebby

 

The balance weight for a 1-piece is a lot smaller than a 2-piece. They aren't close to the same.

The best way is to use zero balanced parts and then it's an easy check to ensure that a replacement flywheel is correct, but for a mild engine it's acceptable to assume a factory weight is OK and swap between parts. Not all engine build are high dollar race engines. If you pulled a low mile L31 from a pickup would you check the balance before swapping the stock weighted flexplate that was on it for a stock weighted flywheel, or would you just bolt it on and run it?

Here is a balanced Scat kit requiring an external weighted flywheel that is not included. They don't have many options but they do sell them.
https://www.summitracing.com/parts/s...make/chevrolet

Scat only sells externally balanced kits that include a flexplate, not a flywheel. If you want a flywheel go internally balanced when buying the engine kit or else you have to match balance the new to the old or you have to just change it and run it.

There are lots of 2-piece rear seal internally balanced 383 kits available from Scat.
https://www.summitracing.com/search/...nce%3Ainternal

This is all fun to speculate on, but if you buy a complete already built 1-piece rear seal engine and if it requires the external weight it will either come with a flexplate or require you to use use a factory weighted flexplate or flywheel. In all cases, if you require a flywheel then you would have to either match balance it to the supplied flexplate or just install one with a weight and run it. No-one catalog builds 383 engines with flywheels.

 

I agree on the neutral stuff......but it is a matter of $$$$$ and engines are not getting cheaper......and the internal stuff is only available in forged.

I know the 1 piece weight is smaller......because the rear counter weight is bigger. They had to.....nobody makes or would make a flywheel/flexplate with extra weight on it.....so they modified the counterweight. Even though the 1 piece is technically "external" is not balanced to the same numbers as a 2 piece external......confusing I know...and irrelevant so i will leave it.

As far as crate engines not coming with flywheels/flexplates for external.......it is part of the reason I would never recommend someone elses build like that. If you bought one from me......it would have the very balancer and flexplate the crank was balanced with on the engine when you pick it up. Everyone will say what I am saying doesn't matter until one guy gets a shaker......
I don't want anybody bringing anything back to me....so I just dot more I's and cross more T's I guess.......
As far as GM's balance......their assembly line spec is + or - 50 grams......so any differences in flywheel weighting are negligible compared to the + or - 2 grams the Pro Shops use. There are L31 350's out there that run silky smooth and others not so much.......the ones that shake a bit are never noticeable to the owner as there is not another to compare it to.....it may not shake much, but it does. A guy who hands me 5k to build a budget 383 will feel that type of shake like it is in their soul.....
Oh well.....good conversation and thanks for listening to my side of it!

Jebby

 

Now you got me thinking. I have a low milage GM ZZ383 I bought used. He kept the flexplate that came with it but left the balancer. I got a new complete flywheel and clutch setup from Mcloud and had them do the balancing on the whole setup.. Their flywheel is neutral balanced as is the balancer that came with the engine. Are you saying that the flywheel/clutch setup is wrong and should be balanced with the crank. I've always had everything balanced together but I always had internal balanced engines. I would think that GM built this as a neutral balanced engine specificly to be able to install aftermarket flywheels and clutches without having them balanced on the crank, (otherwise what is the point of neutral balance.) since they dont come that way from GM. Am I missing something?
Thanks
Dan

 

Neutral balance generally do not get balanced with damper and/or flywheel as there is no need to. If the damper/flexplate/flywheel is a quality, verified neutral piece.....the crank balancer doen't know if it is there or not.

Jebby

 

Your ZZ383 will need a 1-piece rear seal weighted flywheel. See below

Crankshaft The ZZ383 Engine comes with forged crankshaft part number 12489436. The crankshaft features are outlined below:
- 3.800" stroke
- Externally balanced
- 2.45" main journals/2.10" rod journals
- Radii on main and rod journals
- One-piece style rear main
- Number 1 and 4 crank pins hollowed
- Rod and main oil hole chamfered
- 3.000" crank flange bolt circle
- 4340 steel alloy, nitride treated

Taken from https://www.chevrolet.com/content/da...e-19301295.pdf

 

You missed where he said the machine shop neutral balanced his rotating assembly

 

This is where you have to be VERY careful.....if the shop "neutral balanced it" then what flywheel did they use, or did they use one at all ? The external weight on a 1 piece flywheel/flexplate is not a real "external" balance in the 2 piece rear main seal sense. The weight is there solely to compensate for the loss of a weighted crank flange. This is what Lionel and I were bickering about above......
They DO make 100% neutral 1 piece flywheels/flexplates......but unless the assembly was balanced specifically that way....it is not correct to use. It can be confusing as hell....and I have seen many get it wrong.
If the 1 piece crank was balanced for a neutral flywheel.....it would be balanced without one at all..... Consequently, the 1 piece setup has to be balanced with a flywheel/flexplate if it balanced to GM spec.....
Now this is at the discretion of the guy balancing the crank too......some "external" cranks will balance without the weight at all.....some will not. Just pay close attention to detail on who did what. Get a balance sheet and/or talk to the guy who actually balanced it. If it is built by GM, go with their recommendation.

Jebby

 

I'm in this boat currently as I am doing a 383 Forged rotating assembly on a Vortec block, so it will be internally balanced in the 2pc sense, so I will be able to run a neutral balance flexplate and a fluidampr. The local machine shop I am using leaned towards a Scat Crank instead of an Eagle to make the balance job easier.

 

I don't think I missed anything. The question reads rather clearly to me that the clutch assembly is the part that was neutral balanced and the engine has not been touched.

 

The engine is as it comes from GM without the flexplate. I bought the flywheel and clutch assy from Mcloud and had them balance the PP/clutch to the flywheel. Obviously I told them the engine and trans spec and they gave me the proper flywheel recomended by GM for that crank. (external balance/1 pc seal) As far as I can tell, the only balance weight on the FW is a small weight held on with a couple screws. They must just use that same FW without the weight for internal balanced crank assy. Just drill holes or add weight as required.

 

It sounds right then. The weight being there means it's not zero balanced. Possibly, they zero balance the assembly and then they bolted on the standard weight. I don't know what it is offhand, but GM will have a balance spec for the weight to use on their externally balanced engines. So, the clutch you bought will be offset balanced to that standard.

You did post that the flywheel was zero balanced in your last post, and now you're saying it has the weight. Zero balanced was wrong, but having the weight is right.

Your are correct that lots of aftermarket manufacturers make flywheels with provisions for a bolt-on weight to change it between zero balanced and externally balanced. When you buy one of these you get the weight and can add or remove it depending on your needs.

 

John lingenfelter also believed the 5.850 rod length had an advantage. My 88 trans am he built had them very good engine.