To much valve lash ??
Thread Starter
Racer
Joined: Jan 2003
Posts: 383
Likes: 0
From: Columbia SC
To much valve lash ??
I replaced the valve seals on all cylinders, along with the O ring just under the keepers.. I replaced the spark pligs, the wires, dist cap and rotor. And I set the valve lash to 1 full turn past zero play on the pushrod.
Now I have a wicked backfire through the carb.....
Too much valve lash ??
Now I have a wicked backfire through the carb.....
Too much valve lash ??
Thread Starter
Racer
Joined: Jan 2003
Posts: 383
Likes: 0
From: Columbia SC
Also...I reset the base timing, so that is off also... But I got to TDC on #1 and adjusted the distributor to the #1 cylinder so that should start the car. But I have backfire thru the carb big time.
I need help..
I need help..
Drifting
Joined: Nov 2002
Posts: 1,665
Likes: 1
From: Ontario
You're sure you have the distributor in the right place and timing set properly? You could disconnect vacuum advance to help troubleshoot.
Could be a vacuum leak, maybe where the carb meets the manifold.
Could be a vacuum leak, maybe where the carb meets the manifold.
Thread Starter
Racer
Joined: Jan 2003
Posts: 383
Likes: 0
From: Columbia SC
Vac advance is not connected and I never removed the carb from the intake. I am sure I dont have a vacuum problem. I am trying to start this on base timing alone, with a little advance by hand...
??
??
Le Mans Master
Joined: Mar 2004
Posts: 7,493
Likes: 1,502
From: Little Rock AR
Most of the time a beginner will misunderstand the lash procedure where it says "play" in the pushrod. The pushrod will be able to move up and down between your fingers as you tighten the adjusting nut to zero lash. As you get close to zero, the pushrod will not be able to move up and down anymore. It WILL still be able to spin very easily though so that is the key. The pushrod is just not able to move up and down freely anymore. You can tighten the nut 1/4 of a turn farther and that is it.
If you are tightening the nut till the pushrod is tight when spinning, you are probably going too far and the valve will be off the seat causing backfiring.
Loosten all the nuts a couple of turns and try again.
-Mark.
If you are tightening the nut till the pushrod is tight when spinning, you are probably going too far and the valve will be off the seat causing backfiring.
Loosten all the nuts a couple of turns and try again.
-Mark.
Drifting
Joined: Dec 2004
Posts: 1,345
Likes: 3
While I agree a half turn is enough tighter after zero lash, the Chevrolet manual calls for a full turn tighter.
It is possible that when you were runnning loose your lifters did not fully extend prior to tightening them. That could cause you to have a valve hanging open causing a backfire.
It is possible that when you were runnning loose your lifters did not fully extend prior to tightening them. That could cause you to have a valve hanging open causing a backfire.
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Race Director
Joined: Nov 2000
Posts: 11,872
Likes: 12
From: Waterloo ontario Canada
Originally Posted by stingr69
Most of the time a beginner will misunderstand the lash procedure where it says "play" in the pushrod. The pushrod will be able to move up and down between your fingers as you tighten the adjusting nut to zero lash. As you get close to zero, the pushrod will not be able to move up and down anymore. It WILL still be able to spin very easily though so that is the key. The pushrod is just not able to move up and down freely anymore. You can tighten the nut 1/4 of a turn farther and that is it.
If you are tightening the nut till the pushrod is tight when spinning, you are probably going too far and the valve will be off the seat causing backfiring.
Loosten all the nuts a couple of turns and try again.
-Mark.
If you are tightening the nut till the pushrod is tight when spinning, you are probably going too far and the valve will be off the seat causing backfiring.
Loosten all the nuts a couple of turns and try again.
-Mark.
The novice will spin the push rod and this is wrong. Long after all play is taken out the rod still spins.Move it up and down until you have no play or close and then absolute maximum 3/4 of a turn maximum.
Safety Car
Joined: Feb 1999
Posts: 3,631
Likes: 14
From: Fountain Hills AZ
Originally Posted by Pete76Shark
Also...I reset the base timing, so that is off also... But I got to TDC on #1 and adjusted the distributor to the #1 cylinder so that should start the car. But I have backfire thru the carb big time.
I need help..
I need help..
I also agree with the other suggestions that have been made. Too tight a valve lash won't allow the valves to fully close and mixed up wiring will also cause your symptoms.
