so this new 383 kit I bought off ebay, the business said it is neutral balanced and that I need a flexplate and harmonic balancer without the conterweights. now this is for a 1 peice RMS. I am a little smarter then that I think, and should he have said that I can ditch the counterweight on my balancer, and still use my flexplate with the batwing counterweight? my last 383 was balanced at my shop and i had to use the counterweight on my balancer, but this new crank is 'neutral' balanced as the business called it, so i should just ditch the counterweight and call it good? or am i shopping for a non existant flexplate?

 

If your 383 is internally balanced, then you should be able to use a stock balancer and stock flexplate from a 305 or 350.

 

A neutrally balanced crank means it has enough mass on the counterweights to be considered an internally balanced crank. It actually has an additional counterweight added to do this.

An externally balanced crank requires balanced weight on the outside of the engine to balance out the mass of the crank. The 400 SBC crank didn't have enough room inside the block for the extra mass of the longer stroke so GM made it externally balanced. They did this by adding a counterweight to the vibration dampener and to the flexplate/flywheel. The flexplate/flywheel is also indexed with a dowel so that it can only be installed in one position maintaining the position of the "batwing" in relation to the crank.

Along comes the aftermarket and they produce a 400 crank designed to fit into a 350 block to make a 383 and make it internally balanced. All this means is that you don't need to buy a dampener and flexplate/flywheel designed for a 400. You simply use a neutrally balanced dampener and flexplate/flywheel for a 350 and bolt them on.

Now this doesn't mean your rotating assembly is balanced. Internal/external balance just means where weight is located to balance the crankshaft itself. The amount of reciprocating weight from the rods, pistons, rings etc still need to be balanced out and the crank counterweights need to be adjusted to match the reciprocating weight.

 

i think basically external means a weight on the wheel/plate and/or balancer

and internal means the weight is on the crank itself and not on any of the parts, the parts for internal balance are neutral

like apeiron said, if the crank is internal balance then you can use any sbc parts on the crank, other than 400 or 454

that includes 265 267 283 302 307 327 350 396 402 427

good luck

 

well the problem is, it seems that all flexplates regardless, have the batwing counterweight on it. and all flexplates listed for my 1peice RMS specify external balance. will this flexplate still work on an internal balance and I just leave my weight off the balancer?

 

Having the weight on the flex plate DOES NOT make it "external balance".

A 305, or a 350, or a 383 built with an "internal balance" crank, is INTERNALLY BALANCED. It will STILL require the batwing weight.

"Internal" and "external" balance DOES NOT refer to which side of the oil seal, or even which side of the crank/flywheel junction, that the rearmost bit of counterbalance is located on.

If your crank is "internally balanced", it will use a STOCK flex plate or flywheel; i.e., WITH the little weight.

 

Man, TraviZ, you're making this much too hard. The batwing weight is part of the "neutral" balance 1-piece rear main seal flexplate. It's as simple as that. Leave it on, run it, be done with it.

This "internal" and "external" balance stuff is pure semantics convention, nothing else. Don't get caught up in the technical purity of the description.

 

The reason I argue this, is even today I called the shop again to clarify, and they keep telling me to get a neutral balancer and flexplate.. I explained to them its a 1 peice and that i only find them with the weights, so they give me a phone number to a place that could 'probably' get me the flexplate without a weight on it. is it possible that a crank could have been balanced for a neutral (no counterweight) flexplate? and that the guys i bought my kit from are smoking crack when they balanced it?
if you can tell me that its impossible to balance a rotating assembly for a 1peice rms without that counterweight on just the flexplate. then i will feel confident.

 

What's possible? Most anything.

What's likely? "What we got here is a failure to communicate."

The batwing weight is simply part of the one-piece rear main seal flexplate. That is not a one-piece rear main seal with external balance weights. Get that out of your head. For someone to go to the trouble to figure out what the balance would be without that weight is beyond reasonable. When I had my rotating assembly balanced, I gave them my flexplate with the understanding that they would not alter the flexplate as part of the balancing process. That was simply because the guy doing the work had only dealt with 2-piece rear main assemblies in the past, and didn't have a one-piece flexplate or flywheel. FWIW, it is as smooth as you could ask for.

Put the flexplate on. If you have vibration when you start up the engine, wack off the batwing. If it doesn't go away, pull your engine and have them do it right. And buy a new flexplate.

 

thats alot of work for a guess. but I suppose thats what I have to do. my last engine was balanced but they needed the flexplate and balancer, but they were not touched per say.

I'll wait and see what my shop says, they were gonna call there balancer guy and see what he had to say.

 

Surely the weight on the flexplate is to balance the flexplate as an individual peice (much like you would a car wheel/tyre), regardless of the balance of the crank?

 

uhhh hold up!

before you have that thing bablced, be sure you do a cylinder to cylinder mockup to make sure things are going to clear, the last thing you want to do with a stroker is start to grind things after the balance....

had to learn that one the hard way!

 

If this is an internally balanced engine AND the shop did the complete balance with out the flywheel there then you HAVE to have a zero balanced flywheel.

Basicly if you took in a crank pistons etc and said balance this and they didn
t ask for the balancer or flywheel and in some case pressure plate, I would smack them and assume you need them zero balanced.

I would call to make sure, but how can a shop account for a balance of a flywheel if they don't know what that balance is???

 

i to have a balance prob,i bought crank i thought was "internal" balance so i ran it with stock 350 balancer and flexplate and it shook like crazy.i took it to the shop to get the rotating assembly "balanced", he started his work and said it was "external" and i need a 400 balancer and nothing about a flexplate and balanced it with 400 balancer and stock flexplate.now it shakes half as bad. i dont know if he didnt do a good job or i need a flexplate for external balance, since he didnt say anything about it. any comments?

 

They may assume you'll use a stock-balance spec flywheel.
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