Compression problems - 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 02-17-2008, 09:59 AM
427feracer's Avatar
First On Race Day
 
Last photo:
Join Date: Jan 2008
Location: Garden plain
Age: 23
Posts: 71
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Compression problems

Hey guys I was wondering what the actual psi for a cylinder on a 1968 390 2v?
because my engine wont run so i checked spark, timing, valves and the fuel system and there all fine so i went to my friends to barrow a compression Gage. Well i hooked it up and my engines psi was around 60 psi doubtfully enough to even run it. So my question is will it still run? And is it the rings or the valve seals on the heads or would it be good to replace both?

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 02-17-2008, 12:14 PM
Member
 
Join Date: Jul 2005
Location: Montana
Posts: 98
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Factory new compression pressure is 180#. The 60# you have is not enough for it to start with the starter. If you have a manual transmission, you may get it going with a steady push down the road, in gear with the key on. Has the engine been sitting for a while? If so the rings are probably stuck. The only way to tell for sure if its the rings or the valves is to do a dry, then wet compression test on all cyls. one at a time. The wet test consists of squirting a couple shots of engine oil in the spark plug hole then test compression on that cyl. If you have a substantial increase in compression, it will be the rings, if no major change, it will be leaking valves. DO NOT try to road start by towing--You have a 99% chance of rear-ending the tow rig if it starts.
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 02-17-2008, 12:19 PM
richard stewart 3rd's Avatar
Registered User
 

Last journal entry: 351W rebuild
Last photo:
Join Date: Jan 2006
Location: tremont, pa.
Age: 70
Posts: 2,218
Wiki Edits: 0

Thanks: 14
Thanked 15 Times in 14 Posts
Hi,
Most engines have 140 to 160# of compression,
w/no more then a 10% difference between cylinders,
A low reading on one cylinder is usually an E-valve
low compression in two cylinders adjacent to each other is usually a head gasket, low compression in all cylinders usually means a rebuild is necessary.
When you do the test, you should have all the spark
plugs out & the throttle wide open, & the coil grounded or discoed.
Good luck,
Rich
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 02-17-2008, 12:25 PM
justold's Avatar
Registered User
 
Join Date: Sep 2003
Location: South Jersey
Age: 67
Posts: 192
Wiki Edits: 0

Thanks: 0
Thanked 4 Times in 4 Posts
If a little oil in the cylinders doesn't bring up the compression and it is still about #60 across the board , I would give the timing chain a good look .
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
compression ratio compared to compression PSI squids1 Engine 14 12-29-2010 12:36 AM
Compression height question DaSouthWon Engine 7 11-12-2006 10:41 PM
350 problems Dead Cylinder! wed68 Engine 3 04-03-2005 10:15 PM
Compression with supercharger chevyelc81 Engine 3 03-18-2004 06:50 PM
High compression ratio pistons invincible Engine 6 09-22-2003 11:16 PM


All times are GMT -6. The time now is 08:37 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.