externally balanced vs interally balanced? - Hot Rod Forum : Hotrodders Bulletin Board
Hotrodders.com -- Hot Rod Forum



Register FAQ Search Today's Posts Unanswered Posts Auto Escrow Insurance Auto Loans
Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Engine
User Name
Password
lost password?   |   register now

Reply
 
LinkBack Thread Tools
  #1 (permalink)  
Old 06-15-2009, 02:25 PM
Registered User
 
Last photo:
Join Date: May 2009
Location: Ohio
Posts: 12
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
externally balanced vs interally balanced?

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?

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 06-15-2009, 02:37 PM
Registered User
 
Last photo:
Join Date: Apr 2007
Location: Seattle, Wa
Posts: 7,095
Wiki Edits: 0

Thanks: 4
Thanked 541 Times in 457 Posts
Quote:
Originally Posted by bwomp969
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
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 06-15-2009, 02:59 PM
79monster's Avatar
Registered User
 
Last photo:
Join Date: Oct 2008
Location: San Diego, Ca
Posts: 29
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
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?
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 06-15-2009, 03:05 PM
Registered User
 
Last photo:
Join Date: Apr 2007
Location: Seattle, Wa
Posts: 7,095
Wiki Edits: 0

Thanks: 4
Thanked 541 Times in 457 Posts
Quote:
Originally Posted by 79monster
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
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 06-15-2009, 03:14 PM
79monster's Avatar
Registered User
 
Last photo:
Join Date: Oct 2008
Location: San Diego, Ca
Posts: 29
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
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?
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 06-15-2009, 04:21 PM
Decadent pianoplayer
 
Join Date: Nov 2003
Location: Sweden
Posts: 161
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 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.
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 06-15-2009, 04:43 PM
Steel's Avatar
The Ultimate Lurker;)
 
Last photo:
Join Date: Apr 2008
Location: Fostoria, Ohio
Age: 42
Posts: 113
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 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....
Reply With Quote Quick reply to this message
  #8 (permalink)  
Old 06-15-2009, 04:47 PM
Registered User
 
Last photo:
Join Date: Apr 2007
Location: Seattle, Wa
Posts: 7,095
Wiki Edits: 0

Thanks: 4
Thanked 541 Times in 457 Posts
Quote:
Originally Posted by 79monster
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
Reply With Quote Quick reply to this message

Recent Engine posts with photos

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Hot Rod Forum : Hotrodders Bulletin Board forums, you must first register.
Please enter your desired user name (usually not your first and last name), your email address and other required details in the form below.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Externally Balanced engines and Harmonic dampers... PairOf69's Engine 1 08-21-2008 08:16 AM
Internally vs Externally Balanced Crankshaft leejoy Engine 6 01-03-2007 04:19 PM
How to tell if the engine is internally or externally balanced 84Z Engine 9 01-02-2005 02:15 PM
internally or externally balanced? Fizz Engine 2 05-07-2004 08:31 AM
internally or externally balanced??? chevyelc81 Engine 11 02-13-2004 10:12 PM


All times are GMT -6. The time now is 02:10 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.