The 1947 - Present Chevrolet & GMC Truck Message Board Network







Register or Log In To remove these advertisements.

Go Back   The 1947 - Present Chevrolet & GMC Truck Message Board Network > 47 - Current classic GM Trucks > The 1967 - 1972 Chevrolet & GMC Pickups Message Board

Web 67-72chevytrucks.com


Reply
 
Thread Tools Display Modes
Old 05-02-2021, 08:03 PM   #1
kcstreetracer
Registered User
 
Join Date: Mar 2019
Location: Cleveland MISSOURI
Posts: 53
Timing and balancer help!

Ok fellas, I have a truck I've been building the past few years
And have it to the point I'm ready to get it running. But I am having some timing issues I believe.

I have it close enough on timing that it runs. But I can't get much run time because I'm worried it has some pre-ignition or detonation. Its not rod knock I'm sure of. Basically as the cam lopes as it fires it pops and it sounds like its coming out of the carb. Its not every cycle but almost. I've tried turning the distributor but no luck.

Motor is a 355 with 234/488 cam,sportsman 64cc heads,single plane,fts 750 mechanical secondary carb, hei with heavy and light springs.Have 93 octane in it. I believe compression is probably around 10 to 1

I'm not sure if my balancer is correct for my timing tabs. I can't seem to find anything solid on it. The # is 7704 which i believe is a pre 69 8" balancer? My timing tab is bolted on the cover and tdc is about 2 o'clock. The timing mark on the balancer is just a hair to the left of the keyway. I originally had dropped the dizzy in at tdc, but redid it to what I believe is 8 btdc which seemed to help a tad. Starts easier and idles a bit better. I have a piston stop coming to try and get it but this is all new to me, although I'm pretty decent with a wrench the old school stuff is new to me. Im just wondering if my issue is what I think it is or if I need to focus my attention elsewhere. Thanks
__________________
1968 C10 SWB, mild 355,5/7 drop, budget frame off, piecing it back together!
kcstreetracer is offline   Reply With Quote
Old 05-02-2021, 08:30 PM   #2
truckster
Senior Member
 
truckster's Avatar
 
Join Date: Jan 2001
Location: Orem, Utah
Posts: 6,388
Re: Timing and balancer help!

The only way to be sure of TDC is a piston stop. It replaces the #1 plug and lets you determine exactly where TDC is.

You can buy one:
https://www.summitracing.com/search/...e/piston-stops

or build one:
https://www.hotrod.com/articles/wren...y-piston-stop/

Once you know for sure where TDC is, you can set your timing with confidence.
__________________
I have sworn upon the altar of God, eternal hostility against every form of tyranny over the mind of man. - Thomas Jefferson
truckster is offline   Reply With Quote
Old 05-02-2021, 08:42 PM   #3
jocko
Senior Member
 
jocko's Avatar
 
Join Date: Oct 2009
Location: Burleson, TX
Posts: 17,121
Re: Timing and balancer help!

Recall there are 2 TDCs, you want to set your distributor rotor up to just be starting to touch the #1 plug wire tower contact when your balancer is at approx 8-10 deg BTDC on the compression stroke. Thought I'd mention just in case.

Last edited by jocko; 05-02-2021 at 08:53 PM.
jocko is online now   Reply With Quote
Old 05-02-2021, 08:56 PM   #4
kcstreetracer
Registered User
 
Join Date: Mar 2019
Location: Cleveland MISSOURI
Posts: 53
Re: Timing and balancer help!

Thanks for the replies. It is dropped in at 8 btdc on compression stroke.

Just curious, is that popping im hearing most likely pre ignition or detonation?
__________________
1968 C10 SWB, mild 355,5/7 drop, budget frame off, piecing it back together!
kcstreetracer is offline   Reply With Quote
Old 05-02-2021, 10:04 PM   #5
geezer#99
Registered User
 
geezer#99's Avatar
 
Join Date: Aug 2009
Location: Bowser
Posts: 12,242
Re: Timing and balancer help!

That popping might be a valve problem.
Was the motor broke in right?
Like 1500 to 2000 rpm on first start.
geezer#99 is online now   Reply With Quote
Old 05-02-2021, 10:23 PM   #6
kcstreetracer
Registered User
 
Join Date: Mar 2019
Location: Cleveland MISSOURI
Posts: 53
Re: Timing and balancer help!

Quote:
Originally Posted by geezer#99 View Post
That popping might be a valve problem.
Was the motor broke in right?
Like 1500 to 2000 rpm on first start.
Yes it was. First one got 10 minutes at 2-3k had a issue a d shut it down. Fixed problem and went another 15
__________________
1968 C10 SWB, mild 355,5/7 drop, budget frame off, piecing it back together!
kcstreetracer is offline   Reply With Quote
Old 05-02-2021, 10:29 PM   #7
Willys_MB
Active Member
 
Willys_MB's Avatar
 
Join Date: Apr 2017
Location: Boise, ID
Posts: 632
Re: Timing and balancer help!

I was having this issue a year or so ago. It was all fixed once I spent the time and researched how to tune my carburetor (Holley 4150). I’d suggest you start there and work your way towards the more complex issues.

When checking timing are you plugging/pinching your vacuum advance line?
__________________
1968 GMC C2500 Long Bed Fleetside
Willys_MB is offline   Reply With Quote
Old 05-02-2021, 10:40 PM   #8
RustyPile
Registered User
 
RustyPile's Avatar
 
Join Date: Dec 2017
Location: Elkhart, Texas
Posts: 697
Re: Timing and balancer help!

Quote:
Originally Posted by kcstreetracer View Post
Thanks for the replies. It is dropped in at 8 btdc on compression stroke.

Just curious, is that popping im hearing most likely pre ignition or detonation?
I don't remember the exact years, but some years the timing tab was located at 12 o'clock on the chain cover behind the water pump.. The balancer was marked accordingly.. If that balancer is used in conjunction with the tab located at approximately 2 o'clock, the engine can be made to run but the timing cannot be set properly.. Be sure you have "matching" tab/balancer..

If those two parts are correct, and the timing is set properly using a timing light, the popping sound is caused by something else.. Most likely causes are valves are set too tight or camshaft lobe is going away...
RustyPile is offline   Reply With Quote
Old 05-02-2021, 10:41 PM   #9
kcstreetracer
Registered User
 
Join Date: Mar 2019
Location: Cleveland MISSOURI
Posts: 53
Re: Timing and balancer help!

Yes vacuum is disconnected and plugged on carb and distributor
__________________
1968 C10 SWB, mild 355,5/7 drop, budget frame off, piecing it back together!
kcstreetracer is offline   Reply With Quote
Old 05-02-2021, 11:29 PM   #10
truckster
Senior Member
 
truckster's Avatar
 
Join Date: Jan 2001
Location: Orem, Utah
Posts: 6,388
Re: Timing and balancer help!

Quote:
Originally Posted by kcstreetracer View Post
I have a piston stop coming to try and get it but this is all new to me, although I'm pretty decent with a wrench the old school stuff is new to me. Im just wondering if my issue is what I think it is or if I need to focus my attention elsewhere. Thanks
OK, that's what happens when I'm reading posts and playing with my grandchildren at the same time. You're on the right track; I would start by verifying your TDC matches your timing tab. I read somewhere that 90% of carburetor problems are timing problems. I don't know how true that is, but I do know it's pretty much impossible to get anything else right until the timing is set.
__________________
I have sworn upon the altar of God, eternal hostility against every form of tyranny over the mind of man. - Thomas Jefferson
truckster is offline   Reply With Quote
Old 05-03-2021, 07:11 AM   #11
Ol Blue K20
truck of four colors!

 
Ol Blue K20's Avatar
 
Join Date: Nov 2012
Location: Vacaville , CA
Posts: 13,930
Re: Timing and balancer help!

I had the symptoms that sounded like that once. I discovered 5 and 7 wires were crossed and that's why it had the pop out the carb. Check your wires, it's the little things we overlook sometimes...
__________________
"Some Days Chickens And Some Days Feathers"

Dale
XNGH ECV Sam Brannan 1004
Ol Blue K20 is offline   Reply With Quote
Old 05-03-2021, 08:35 AM   #12
Grumpy old man
Senior Member
 
Grumpy old man's Avatar
 
Join Date: Dec 2013
Location: Gods country East,Tn
Posts: 7,197
Re: Timing and balancer help!

Is this the same engine you were having problems with a few weeks ago ?

https://67-72chevytrucks.com/vboard/...d.php?t=820812


Post up a few pictures of the engine , Pictures always help .
__________________
Grumpy old man is offline   Reply With Quote
Old 05-03-2021, 08:40 AM   #13
BigBird05
Senior Member
 
Join Date: Aug 2019
Location: Cheraw
Posts: 756
Re: Timing and balancer help!

You have a piston stop on order, thats good. But let me ask if you know how to use it to set TDC on the balancer? You rotate the engine either clock wise or counter clockwise till it stops. Put a mark on the balancer at 0 at the timing tab. Then rotate the engine the other direction till it stops. Put another mark on the balancer. Half way between those marks is TDC. It helps to mark TDC on the pulley also because faulty balancers do move over time changing the location of the timing mark.
BigBird05 is offline   Reply With Quote
Old 05-03-2021, 10:19 PM   #14
CC69Rat
Senior Member

 
CC69Rat's Avatar
 
Join Date: Jan 2011
Location: Chattanooga TN
Posts: 6,007
Re: Timing and balancer help!

Quote:
Originally Posted by Ol Blue K20 View Post
I had the symptoms that sounded like that once. I discovered 5 and 7 wires were crossed and that's why it had the pop out the carb. Check your wires, it's the little things we overlook sometimes...
My first thoughts too.. easy to miss it.

18436572. 5 and 7 are right beside each other in the firing order and on the block, so it's easy for those wires to get swapped.
__________________
Chad

1967 C10 SWB - Project Savannah - 6.0/4L80 *Currently underway*
1968 C10 SWB - TOTY 2018, 50th Anniversary Tribute Project * Sold * Pride and Joy
1986 Silverado Short Fleet - Scarlet *Sold*
1985 Silverado Short Fleet *Sold* (Dad has it now)
2017 Ram 2500 Crew Cab 4x4 6.4L (daily)
2001 Jeep Cherokee XJ - Lifted
2003 S10 Blazer 4 door - Dropped, Americans
2013 Honda Accord EX-L v6 Coupe 6spd (wife's ride)
CC69Rat is offline   Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not 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

Forum Jump


All times are GMT -4. The time now is 07:11 PM.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2021, vBulletin Solutions Inc.
Copyright 1997-2020 67-72chevytrucks.com