Hot Rod Forum banner
1 - 8 of 8 Posts

·
Registered
Joined
·
15,300 Posts
bwomp969 said:
I'm looking to rebuild my 1983 350sbc and I saw on jegs.com that their kits are "internally balanced" and "externally balanced" whats the difference?
what do each mean?
Your 1983, 350 is internally balanced and uses a two piece rear seal. Where the 350 is concerned, reference to external balance is aimed at the 86/87 and up engines with a one piece rear seal where reshaping the flywheel/flexplate mounting flange forced a small amount of balance weight be placed externally. This is nothing like the 400 or options on stroker cranks like those of the 383 where a much larger portion of the counter balance is carried on both the flywheel/flexplate and the damper rather than just the crankshaft's counterweights, these are truly externally balanced, but can be modified to internal balance for enough bucks.

This is a long way around to say that the damper and flywheel'flexplate of your 1983, 350 are neutral balanced and that all the crankshaft balance is carried internally on the counterweights.

Bogie
 

·
Registered
Joined
·
15,300 Posts
79monster said:
I have a 383 does that mean im supposed to be externally balanced? do i buy proper flywheel/damper combo? if i dont what could happen?
You need to know where your 383 is starting from, stroker cranks and kits are sold in either external or internal balance. If you get it wrong the engine will shake from being a major annoyance at the minimum to perhaps coming apart at the maximum.

Bogie
 

·
Decadent pianoplayer
Joined
·
163 Posts
The answer is Yes to both questions.
Stock 400 cranks are ext. balanced and internal balanced assembleys are better. External balanced means you have an inbalance but you counter it with weights on the damper and flywheel/flexplate; you average zero inbalance so to speak. Internal balanced means you "zero" any inbalance on each part.
 

·
The Ultimate Lurker;)
Joined
·
113 Posts
I would keep in mind that if you do purchase an internally balanced kit you will also need to purchase a neutral balance flex plate/flywheel and balancer....

I have also heard of guys chiseling the balance weights off of the flexplates so they didn't have the cash to buy the neutral plate but it's not something I would recommend....
 

·
Registered
Joined
·
15,300 Posts
79monster said:
so if i have a stock 400 crank @ 3.75 stroke in a 350 then i should be ext. balanced and if i buy a kit i should get it int. balanced? is there advantages to either?

To start with a 400 crank has to have its mains tuned down to the 350 size main.

Personally I prefer an internally balanced engine. But a 400 crank is designed for external balance and it is quite expensive to convert it back to internal balance, so unless I was taking it racing, I wouldn't go thru the expense to convert it to internal balance.

If you're buying a 383 kit, many manufacturer's offer a choice between internal or external balance, for these I choose internal as much as possible. But here's a place where you want to be careful, if you get a cast iron internally balanced shaft the counterweights are larger and can make fitment past the pan rail and the bottoms of the cylinder bores a bigger problem as more clearance is required. For a cast steel, forging, or billet crank the material is denser than cast iron, this allows for a smaller counterweight so clearancing the block is less of an issue.

Internal balance has two advantages, the first is you use a neutral balanced damper and flywheel/flexplate, this makes field replacement of these items simple since they aren't contributing to the crank balance and replacement won't upset overall engine balance. The second advantage is by taking the counterbalance at each rod journal, bending moments are taken from the adjacent mains which in turn takes the resolution of the local loads off those mains. This reduces the likelihood of a failure of the crank or the main bearings since it's one more force they don't have to resolve into the block. In this regard you can see how much the crank of externally balanced moves when you take it a part and look at the wear patterns on the mains.


Bogie
 
1 - 8 of 8 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top