So why is my shop still trying to tell me that my 89 block one peice rear main seal requires the stupid counterweight on the damper? I thought you only used those stupid weights on the older blocks when you actually put a 400 crank in them. he also says my block is strictly external balance when I thought they were an internal balance engine. Im picking up my peices tomorrow and gonna find a different shop.

 

That would be the smart thing to do.

 

Your shop is correct, all 1986 and later SBC are externally balanced, both the flywheel and balancer are used to balance the engine. If you had a 1985 or earlier engine it would be internally balanced.

 

Well he has a 1 Piece RMS, the weight is just a weight that makes the whole plate neutral, thats it.

I am pretty sure the 2 piece RMS that you are referring too as in 86 and below, are the EXACT same way. The 400 was externally balanced 3rd gens were all internally.

 

Here we go again, with the misinformation about "internal" and "external" balance....

One more time:

Understand how balancing works, and this will become much less mysterious. Start with the basics. For correct dynamic balancing, the counterweight for each rod throw must be split in half, with one half located to each side of the throw.

ALL SBCs except for the 400 are internally balanced. They ALL have enough space between the crank centerline and the bottom of the piston when it's at BDC, to fit a large enough counterweight, to correctly counterbalance the rod throws. They have the front half of the counterweight for the front-most rod throw located between the rod throw and the front of the block, behind the front main bearing. This applies to ALL SBCs EXCEPT FOR 400; "all" means ALL, with no exceptions of any kind for any reason; that includes all years, all sizes, all all all. Consequently, ALL SBCs except for the 400 use a neutral-balance crank damper. See definition of "all" above for further clarification if you think there are any exceptions, or if anyone else thinks that there are.

85-back motors located the rear half of the counterweight for the rear-most throw, on the flywheel flange. It cannot go between the rod throw and the inside of the block, because the oil pump is there. That's why they have that funky shape. The flywheel or flex plate is therefore completely "neutral" balanced.

86-up motors have the flywheel flange that is perfectly round, so that the lip seal will go on it. Therefore that rear-most INTERNAL balance weight, that confusing INTERNAL one that is EXTERNAL to the oil seal, can no longer be located there. Instead, the INTERNAL weight is located on the flywheel or flex plate. This DOES NOT make this weight "external"; it DOES NOT mean that the motor is "externally balanced"; these engines are still INTERNALLY balanced, inspite of the fact that the last little bit of INTERNAL balance weight "looks", to the eyeball, as if it is "external". Not only is it "outside" the block, but also, it is not even part of the crank itself, it is a bolt-on. Do not let that appearance fool you. This DOES NOT make it "externally balanced".

If a shop is telling you that you need an unbalanced crank damper for a 350, DO NOT let them TOUCH your parts!!!! Get over there as quick as you can and pick them up before they destroy something in their stupidity. Take your stuff to someone who knows what they're doing.

I suggest hanging out in the pits at your local circle track, and find out who does the machine work for the cars THAT WIN, and use that shop.

 

Thank you sofakingdom, That's pretty much what I thought, maybe just not wording it right. So in a 383 application, as in my case, since it is an aftermarket crank, I should be seeing it setup just like a 350 correct? no counterweight on the damper?

and for the older blocks that people actually crammed a 400crank in, they would retain that counterweight on the damper correct?

 

Well, it would have been nice if you had mentioned this was a 383.

In that case:

Depends.

Depends upon the way the crank was made. If it was made to use a neutral balance damper and a "standard" one-piece rear main seal flexplate/flywheel, then that's what you should use.

If it wasn't, then you need to use a weighted damper and flexplate/flywheel with the additional balancing.

What does your crank manufacturer say?

 

If your rods are 5.7" or longer, then most likely, it's an internally balanced crank, and would use the regular 350 stuff. In the case of 1-pc RMS motors, it's best to just drop the words "internal" and "external" from your vocabulary altogether; and just use the word "stock". And, DON'T BUY any crank that doesn't support "stock" balance, no matter how cheeeeep it is on eBay (yes, some people have had trouble with that here lately).

You can just look at the counterweights and tell. If they're completely circular, then they're enough for internal balance. If they're "flat cut" on top, such that when the CW is "at TDC" it's not as "tall" as it would be if it was circular, then it's an external balance crank. Remember that the CW is directly opposite the rod throw; i.e. when the piston is at TDC, the CW is at BDC pointing away from the piston; and when the piston is at BDC, the CW is at TDC, pointing up toward the bore, right under the back side of the piston. That "flat cut" is to provide clearance for the bottom of the piston so it doesn't hit the CW.

And, you're exactly right about our "old school" way of building a 383, before you could just buy a "kit" with an aftermarket crank like you can nowadays. We would take a stock 400 crank and turn the mains down to 350 size, and then just use stock 400 rods and 350 pistons; and of course, the 400 externally balanced damper and flywheel. A little balancing would usually be required, because the 350 pistons are a little lighter than 400 ones; but not a whole lot.

Stock 400 rods, incidentally, are designed in such a way that the block doesn't have to be ground for them to clear, and they don't hit the cam. They're different from (shorter than) other SBC rod bolts, and the place on the main piece of the rod where they go through isn't as thick. And, their head has an angle cut off of the side. Stock 350 rods aren't like that, so the block has to be clearanced to them.... and sometimes THEY have to be clearanced to the cam. Hence, small base circle cams, to minimize or eliminate that source of interference.

 

Thanks again sofakingdom, I do know my Eagle crank has the full round counterweights, they are not chopped at the top as you mention, so I can safely say to ditch the counterweight on my balancer my shop says I needed. ( I think they are stuck on the old school ways.)
I shouldnt say this but this same shop balanced my last engine in which they still required the stupid weight on the front balancer, this was also with a different eagle 383 crank, and when I got it back the counterweights were full of holes and they said it was really out of whack and had to do a lot of work to make it balance, now I probably know why lol.

 

custom engines can be assembled either way. find out from who is doing the rotating assembly what balance it needs. my eagle 383 kit is balanced like a 400. external.

 

is yours a one peice or two peice RMS?

 

2

 

Thats the difference here. 1peices are much different.

 

no they are not! dont make a mistake call eagle or look on summitracing.com
there are 383 internal and external balnce reguardless of the one or 2 peice block seal.

 

ESP-B13004L03053 summitracing.com

 

That part # is EXTERNAL BALANCE (uses 400 parts); 2 pc RMS

http://www.eaglerod.com/products/Che...ssemblies.html down at the bottom

They supply a stock-replacement-grade damper and flex plate.

Looks like if you have a stick, you need to get a 305 flywheel "unbalanced" to the stock 400 spec; or use a "pork chop".

I would not use that kit if I could help it. I'd strongly recommend buying the 13054 kit instead. You'll eat up the extra $100 or whatever IN A HURRY with a bunch of fooling around.

 

I dont know if you are talking to me or rjt76, The crank I have is part number 435337505700 and as listed, its internal balance. and I have eagle H beam 6" rods. not that that matters.

 

robert i sure hope you have this someplace you can cut and paste it to here. i'd of given up by now.

 

bjankuski, I hope you're following all this. Your post was wrong regardless of the missing information that was later provided.

For the record, the fact that it is a 383 crank, and the p/n, would have been good info to have had in the very first post.

I believe the answer still stands - find another shop; you don't need a weighted damper; you only need a "standard" "factory" "stock" one-piece rear main seal flexplate/flywheel.

 

I was just trying to help. if you now yours is internal balance then whats the issue? get another shop! if you have to babysit them they have to go!
I thought you were unsure of what you had. I wanted to be clear they do make them both ways.