72 LT1 Timing Problem - 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
lost password?   |   register now

LinkBack Thread Tools
  #1 (permalink)  
Old 08-30-2006, 07:03 AM
Registered User
Join Date: Aug 2006
Location: Detroit
Posts: 2
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
72 LT1 Timing Problem

The nylon coated cam gear on my 72 LT1 Vette failed. I replaced the timing gears with a dual sprocket set. I am 98% confident that everything is aligned properly. However, I have been unable to get the timing set to the spec of 4 deg btdc. I have been able to get the engine to run at about 28 deg btdc but when I try to advance/retard the distributor, the engine starts to stall. I checked the vacuum which is only about 2" at idle and about 14-15" if I race the engine. Is the low vacuum due to the bad timing or the bad timing due to the poor vacuum. or is soming else going on? I hate to pull everything apart to get to the timing gears again. Any Ideas what to check next?

Reply With Quote Quick reply to this message
Sponsored Links
  #2 (permalink)  
Old 08-30-2006, 09:51 PM
Last photo:
Join Date: May 2003
Location: Shreveport LA
Age: 67
Posts: 5,106
Wiki Edits: 0

Thanks: 0
Thanked 1 Time in 1 Post
Have you checked for a big vacuum leak?
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 09-04-2006, 09:27 AM
Registered User
Join Date: Aug 2006
Location: Detroit
Posts: 2
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
I went back to the beginning and pulled the timing cover. I remounted the balancer with the cover off and confirmed that the gear marks line up when the balancer mark is at tdc. I also made a timing wheel with 5 deg increments that I mounted to the balancer. I went to the intake valves and confirmed that the push rod starts to move around 35 deg btdc (spec in Chilton's was 36 deg). I also tweaked the valve lash to specs of .024/.030 plus .002 for a cold engine.

At this point, the engine runs smoothest at 20 deg btdc. Idle is 1050 - 1100 rpm (spec is 900). Engine vacuum is vibrating between 13.5 and 14.5" (probably worn valve guides).

If I adjust the distributor a little, I can get to 8 deg btdc (spec is 4 deg). idle is 900 rpm. Vacuum, however, drops to 10.5 to 11.5". If I race the engine vacuum drops to 4" and goes up to 22". When I release thottle vacuum drops to 10" and settles between 10.5 and 11.5.

At this point without chasing more major repairs, should I settle for the smoother idle and higher vacuum and adjust down my idle or should I keep it around the 8 deg btdc with the lower vacuum? Or am I missing something else that is relatively simple?
Reply With Quote Quick reply to this message

Recent Engine posts with photos

Quick Reply

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:
Please enter a password for your user account. Note that passwords are case-sensitive.
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:
Please select your insurance company (Optional)


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
Port or Full time vacuum cool rockin daddy Engine 129 10-05-2010 03:00 PM
305 Timing problem mtncat Engine 3 03-15-2006 09:30 PM
SBC timing problem saenz5 Engine 5 02-15-2004 09:40 PM
Timing problem!! KeithB123 Engine 6 09-12-2003 08:42 PM
alignment problem on the 72 72 Z28 Engine 4 12-15-2002 01:27 PM

All times are GMT -6. The time now is 09:39 PM.

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.