SBC Valve spring pressure - 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 09-07-2010, 05:42 PM
Member
 
Join Date: Dec 2001
Location: Macedonia, Ohio
Age: 78
Posts: 318
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
SBC Valve spring pressure

I was out today and on the way back my SBC started clacking(rocker arms?) and as soon as I went to an idle it stopped clacking. What it seems to be doing is back firing/missing out the exhaust. I checked the timing/wiring/vacuum leaks and what I have come to the conclusion is that one or more of the exhaust valve springs are getting weak. At idle it purrs like a kitten but at 2000 rpm and up it pops/misses thru the exhaust not the carburetor. If the springs are weak can you compress(move them at all) them a little by hand? It seems to me that the springs are weak. They are very I mean very old. How can you measure spring pressure without taking them to a machine shop?
Thanks - Jerry

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 09-07-2010, 06:52 PM
F-BIRD'88's Avatar
Yada Yada Yada
 
Last photo:
Join Date: Oct 2005
Location: Ontario, Canada
Posts: 9,206
Wiki Edits: 0

Thanks: 5
Thanked 388 Times in 382 Posts
Use a bathroom scale and a drill press. Check them at 1.75" and 1.70".

stock 85# Z28 #105-115 stock diameter race 125-135#
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 09-07-2010, 07:24 PM
Registered User
 
Join Date: Nov 2005
Location: Duffield ,Va
Age: 67
Posts: 526
Wiki Edits: 0

Thanks: 0
Thanked 1 Time in 1 Post
If they are (very old) replace them,new one's are not that expensive. And while you got them off check for valve guide slop. Also may have lobes going on camshaft.


Quote:
Originally Posted by fred56
I was out today and on the way back my SBC started clacking(rocker arms?) and as soon as I went to an idle it stopped clacking. What it seems to be doing is back firing/missing out the exhaust. I checked the timing/wiring/vacuum leaks and what I have come to the conclusion is that one or more of the exhaust valve springs are getting weak. At idle it purrs like a kitten but at 2000 rpm and up it pops/misses thru the exhaust not the carburetor. If the springs are weak can you compress(move them at all) them a little by hand? It seems to me that the springs are weak. They are very I mean very old. How can you measure spring pressure without taking them to a machine shop?
Thanks - Jerry
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 09-08-2010, 04:04 AM
Registered User
 
Join Date: Jul 2008
Location: NC
Age: 33
Posts: 240
Wiki Edits: 0

Thanks: 0
Thanked 1 Time in 1 Post
What the gentleman above said... hope it's not cam lobes.
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 09-08-2010, 04:47 AM
EOD Guy's Avatar
Registered User
 
Last photo:
Join Date: Aug 2010
Location: Alabama
Posts: 2,128
Wiki Edits: 0

Thanks: 1
Thanked 149 Times in 137 Posts
Might ck your dizzy cap and rotor, mine was not secured properly, which led to a misfire condition, which led to plug fouling etc..... new plugs, cap and button ...... runs like it used to.
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 09-08-2010, 05:55 AM
Duntov's Avatar
Visit the NASCAR Hall of Fame
 
Join Date: Jun 2010
Location: Near Charlotte
Posts: 411
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Possible leaky valve?

Quote:
Originally Posted by F-BIRD'88
Use a bathroom scale and a drill press. Check them at 1.75" and 1.70".

stock 85# Z28 #105-115 stock diameter race 125-135#
Back in the Seventies I bought my first adapter in order to pressurize a cylinder so I could replace the valve seals without removing the head.

I realized during the course of that job that it was the best diagnostic tool I had ever had. The first cylinder I pressurized was spewing pressure out of the ex valve/tail pipe, so fast I was worried if it would stay up.

Another cylinder had an intake valve nearly as bad and the carb belched up a puff fuel mixture from the intake. Another cylinder had really weak rings.

All the cylinders had a small leak you could hear but if it's bad there is no mistaking it. I keep a kit on the wall and use it once in a while.
Oh, If anyone does this who has never done it before, I recommend a swivel hose and not a quick coupling. Take no chance of it blowing off. keep fingers away from belts and pulleys
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 09-08-2010, 03:21 PM
Member
 
Join Date: Dec 2001
Location: Macedonia, Ohio
Age: 78
Posts: 318
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
SBC Valve spring pressure

Thanks for the helpful information I am going to pull the heads over the winter and replace all the old stuff. I like the idea to use the bathroom scales to check for pressure, I will remember that. About the distributor I already checked it and while I have the motor apart I will check the cam lobes.

Thanks again for your help.
Jerry
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
SBC valve spring retainers...... 383SBC Engine 6 07-13-2010 01:00 PM
What type of cam has the least chance of failing? 4speed57 Engine 25 01-29-2010 04:46 PM
valve spring pressure GMR Engine 8 11-14-2008 08:37 AM
sbc valve spring notsure Engine 4 07-10-2008 07:22 PM
SBC Valve Spring Setup malc Engine 16 11-10-2006 02:06 PM


All times are GMT -6. The time now is 11:59 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.