does my rotating assembly need 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> Engine
User Name
Password
lost password?   |   register now

Reply
 
LinkBack Thread Tools
  #1 (permalink)  
Old 07-18-2005, 05:12 PM
Mad Maggot's Avatar
The lean mean donut machine
 
Last photo:
Join Date: Aug 2004
Location: Red Deer, Alberta, Canada
Age: 30
Posts: 386
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
does my rotating assembly need balancing?

I'm wondering if I purchase a Scat crank that is balanced and ready to go out of the box, and matched it up with close tolerance (+/- 1 gram) rods and equal weight pistons, if I need to get this assembly balanced. I know this is a costly procedure, and logic dictates that if all the pieces are already balanced, then there is no weight discrepancy from one part to another, so if this is the case, would it be prudent to skip the balancing? I plan on building another SBC 400 and I'm going to rev it around 6000-6200 RPM. I will get good quality forged parts, in case this is a concern.
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 07-18-2005, 05:53 PM
King of my Man-cave.
 
Last photo:
Join Date: Nov 2003
Location: Michigan
Age: 55
Posts: 2,836
Wiki Edits: 0

Thanks: 2
Thanked 4 Times in 2 Posts
There is no such thing as a crank that is balanced and ready to go out of the box. The crank has to be balanced to YOUR particular parts combination. And rod sets and piston sets are rarely within a gram or so. I have checked more that a few "balanced assemblies" that were in need of a good balance job.

If you think that you can gather a bunch of parts that are close enough to not need balancing, think again.

tom
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 07-18-2005, 05:56 PM
coldknock's Avatar
Member
 
Last photo:
Join Date: Feb 2004
Location: Social Circle, Ga.
Age: 42
Posts: 1,528
Wiki Edits: 0

Thanks: 0
Thanked 1 Time in 1 Post
Yep, in spite of the rods and pistons being matched sets, the crankshaft isn't balanced until the machine shop dude weighs them and actually does the job according to the bob-weight established with the pistons and rods you have.

No rough balancing job can account for all the different rod and piston weights. They have a "target" bob-weight that you can work toward when you purchase the rods and pistons but it still needs to be balanced.

Larry
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 07-18-2005, 07:39 PM
crazy larry's Avatar
Member
 

Last journal entry: better comparison before and after shots
Last photo:
Join Date: Oct 2002
Location: East Texas
Age: 42
Posts: 2,299
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
if you've spent the money on a new crank, it would be most prudent to have it balanced. money well spent.
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 07-18-2005, 10:17 PM
Mad Maggot's Avatar
The lean mean donut machine
 
Last photo:
Join Date: Aug 2004
Location: Red Deer, Alberta, Canada
Age: 30
Posts: 386
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
D'OH!!!!!!!!!!

That adds like $700 to the cost of my engine... CH-CHING!!!

I guess if it is necessary I won't cheap out.
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 07-19-2005, 05:07 AM
Member
 
Last photo:
Join Date: Jan 2005
Location:
Posts: 3,707
Wiki Edits: 0

Thanks: 0
Thanked 2 Times in 2 Posts
Most shop's I've delt with charge about $200 to balance an assembly, I usually weight match the pistons and rods before taking them to the machine shop-saves them a little time.
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 07-19-2005, 08:44 AM
Member
 
Last photo:
Join Date: Aug 2003
Location: surrey bc canada
Age: 73
Posts: 630
Wiki Edits: 0

Thanks: 0
Thanked 9 Times in 9 Posts
re ballance

ballance job hear in surrey bc is 250 that is canadian if you want a phone no mad magot send me a email. frt to and from cant be much. cliff ct1940@telus.net. to not ballance with your investment insane.
Reply With Quote Quick reply to this message
  #8 (permalink)  
Old 07-19-2005, 08:57 AM
Hotrodders.com Moderator
 

Last journal entry: PICTURE TEST
Last photo:
Join Date: Jan 2004
Location: york pa
Age: 52
Posts: 2,795
Wiki Edits: 0

Thanks: 0
Thanked 1 Time in 1 Post
balance

I am not sure if you are getting confused about what a target bob weight is???

Many crank makers will list a target bob weight for the crank. But as Tom and other have stated even if you get your assembly to this target weight it is not even close when you spin the crank.....

So for your answer Yes you need to balance it,,,, no you don't need to pay $700 to get the job done!!!!
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:
If you do not want to register, fill this field only and the name will be used as user name for your post.
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
rotating assembly firestone Engine 1 11-21-2004 09:56 AM
rotating assembly question richardson110 Engine 4 10-03-2004 08:47 PM
Turbo SBC Rotating Assembly KA67_72 Engine 7 07-02-2004 09:29 PM
Balanced Rotating Assembly chevytech Engine 5 05-12-2004 07:54 PM
355 stiff rotating assembly Jared Engine 9 09-02-2003 06:20 PM


All times are GMT -6. The time now is 04:57 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.