Engine Balancing - 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> Hotrodding Basics
User Name
Password
lost password?   |   register now

Reply
 
LinkBack Thread Tools
  #1 (permalink)  
Old 05-08-2013, 05:39 PM
clwhoops44's Avatar
Registered User
 
Last photo:
Join Date: May 2013
Location: Charleston, WV
Posts: 307
Wiki Edits: 0

Thanks: 112
Thanked 19 Times in 18 Posts
Engine Balancing

I have a rotating assembly for a 383 thats already balanced, but plan on switching out the rods to some Scat i beams that are 14 g lighter than the h beams the kit was balanced with. Will the entire thing need rebalanced? its a street/strip 383.. 450-500 hp/tq

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 05-08-2013, 08:33 PM
BOBCRMAN@aol.com's Avatar
Member
 
Last photo:
Join Date: May 2002
Location: Holly, michigan
Posts: 8,244
Wiki Edits: 0

Thanks: 30
Thanked 298 Times in 278 Posts
No, lighter is better. The engine will be slightly "overbalanced" something left turn sportsman racers swear by..
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 05-08-2013, 10:02 PM
vinniekq2's Avatar
Registered User
 
Join Date: Jun 2012
Location: BC,Canada
Age: 56
Posts: 8,680
Wiki Edits: 0

Thanks: 367
Thanked 864 Times in 826 Posts
I once and only once in my life,did not balance an engine.
best machine work to do to any engine
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 05-09-2013, 08:19 AM
Registered User
 
Join Date: Nov 2011
Location: Virginia
Posts: 705
Wiki Edits: 0

Thanks: 0
Thanked 75 Times in 75 Posts
In a manner of speaking, Bob is right. It isn't that "cut and dried", though. IF the "big end" of the rod is very close in weight (a gram or two, no more), but the "little end" is where the significant difference is, THAT is "over-balance" and not a bad thing. Itf the big end is much different, it really should be re-balanced. The "rule of thumb" is, you can go about 10% lighter in the reciprocating mass without worries, but not much at ALL in the rotating mass.

I'm pretty much in agreement with Vinnie. We balance them all, for the most part. Only on "bargain rebuilds" or by customer request, do we not.

Jim
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 05-09-2013, 08:48 AM
Registered User
 
Last wiki edit: General Motors transmissions Last photo:
Join Date: Mar 2006
Location: near Yellowstone park
Posts: 4,479
Wiki Edits: 27

Thanks: 13
Thanked 285 Times in 265 Posts
over balancing

The theory I was told was that when a cylinder Fires it puts more force on the piston and over balancing, having more weight on the crank, can counter act that force.
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 05-09-2013, 02:05 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 clwhoops44 View Post
I have a rotating assembly for a 383 thats already balanced, but plan on switching out the rods to some Scat i beams that are 14 g lighter than the h beams the kit was balanced with. Will the entire thing need rebalanced? its a street/strip 383.. 450-500 hp/tq

The theory I was told was that when a cylinder Fires it puts more force on the piston and over balancing, having more weight on the crank, can counter act that force.
Overbalance is a one -two percent thing not a lot so 14 grams in the total of piston and rod is probably in the range. But overbalance is for a high RPM wide open throttle operation. On the street crusing under part throttle this will shake. This puts a lot of load into the mains and requires a damn good damper hanging on the front of the crank otherwise the twist moments from the crank shake will cause the nose to wander off center taking the number 1 main with it. Breakage of the snout and/or loss of oil pressure from the number 1 main to the number 1 rod from the main being carved up is a fairly common outcome. By the time you belly up to the bar to buy a supergood damper, you could rebalance the crank and take some weight off the counter balances as well, this makes the engine rev faster.

Bogie

Bogie
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 05-10-2013, 08:38 AM
Registered User
 
Join Date: Nov 2011
Location: Virginia
Posts: 705
Wiki Edits: 0

Thanks: 0
Thanked 75 Times in 75 Posts
Agreed with Bogie, excessive over-balance is a "bad" thing. It goes upwards of 7-8% on high revving blown/alcohol engines. I've seen some big (738s, etc) pro-mod types at 10.

The front main "thing" is generally found in Chevy engines, as the thrust is all the way to the rear. Most engines (American V8s) have thrust on #3, at least one on #4 and another on #1, whidch will have less negative effect on the "end" mains.

FWIW

Jim
Reply With Quote Quick reply to this message
  #8 (permalink)  
Old 05-10-2013, 10:36 AM
Registered User
 
Join Date: Aug 2008
Location: kansas
Posts: 51
Wiki Edits: 0

Thanks: 0
Thanked 3 Times in 3 Posts
engine balance sbc

According to David Vizard up to "50 grams of overbalance can be used before there is a detectable loss of smoothness. More than this the engine shakes more than we like. But it is still likely to be less than a balanced 4 cylinder engine"

"Foregoing balancing does not mean there will be more destructive internal engine loads present. The engine is no more likely to fail than a perfectly balanced engine."
Reply With Quote Quick reply to this message
  #9 (permalink)  
Old 05-10-2013, 12:39 PM
Registered User
 
Join Date: Nov 2011
Location: Virginia
Posts: 705
Wiki Edits: 0

Thanks: 0
Thanked 75 Times in 75 Posts
Using a specific "value" in weight applies ONLY to a specific engine. A small block crank weighs about 50 lbs. A big block or Pontiac crank weighs over 70. 50 grams would make a "different" "difference" in these weights. Over-balance should be spoken of in "percentage" unless ALL the parameters are alrready known.

If an engine is far enough "out" of balance, excessive and unusual main bearing wear WILL occur.

FWIW

Jim
Reply With Quote Quick reply to this message

Recent Hotrodding Basics 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
ENGINE BALANCING NAIRB Engine 19 12-29-2013 07:45 PM
Engine balancing Hick_101 Engine 4 01-15-2012 03:21 PM
Engine Balancing brainsboy Engine 5 01-26-2008 05:30 PM
balancing an engine elcaminodragster Engine 11 02-21-2007 08:56 AM
What Really Is Engine Balancing? Canadian Charlie Engine 4 12-03-2005 06:34 PM


All times are GMT -6. The time now is 12:14 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.