How do you determine the correct pushrod length?
07-22-2002, 08:55 PM
#1
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How do you determine the correct pushrod length? I just built my motor, LS6 block, 6.0 heads. After it started I had a miss. I found it to be an exhaust valve staying open all the time. If I loosened the rocker I got my compression back. I called the guy that did the heads and he said to use .025 shorter pushrods which I did. It runs O.K. now but clatters. It sounds like it could be from one or two cylinders. I want to know how to determine exact pushrod length that I will need. It sounds like to get it quiet I might have to use different lengths on different cylinders (maybe some irregularities on the valve job). I talked to one guy who said that you tighten the rocker until there is no slack and then count the turns until it is tight. How many turns should that be? I can't stand the way this new engine sounds. Thanks
07-22-2002, 09:58 PM
#2
TECH Fanatic
Re: How do you determine the correct pushrod length? "I talked to one guy who said that you tighten the rocker until there is no slack and then count the turns until it is tight. How many turns should that be? I can't stand the way this new engine sounds. Thanks"
I can't really understand what your friend is talking about. You may be able to identify which valve has too little or too much preload, but thats all I can see that what he is telling you will prove.
If he knows something I don't know, maybe he should explain a little further to you what his counting turns will acomplish. <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" />
I have never heard anyone needed different length pushrods for various different cylinders.
The valves would really need to be sunk [alot]deeper on a particular cylinder to effect lifter preload that much. I just cant see it happening.
If its really only couple of valves that are clattering, I would think that those valves have collapsed lifters. That would cause lifter noise.
Sorry, I cant answer your question on rocker bolt "turns"...
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<small>[ July 22, 2002, 11:59 PM: Message edited by: Kimchee and Rice ]</small>
I can't really understand what your friend is talking about. You may be able to identify which valve has too little or too much preload, but thats all I can see that what he is telling you will prove.
If he knows something I don't know, maybe he should explain a little further to you what his counting turns will acomplish. <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" />
I have never heard anyone needed different length pushrods for various different cylinders.
The valves would really need to be sunk [alot]deeper on a particular cylinder to effect lifter preload that much. I just cant see it happening.
If its really only couple of valves that are clattering, I would think that those valves have collapsed lifters. That would cause lifter noise.
Sorry, I cant answer your question on rocker bolt "turns"...
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<small>[ July 22, 2002, 11:59 PM: Message edited by: Kimchee and Rice ]</small>
07-23-2002, 12:12 AM
#3
TECH Fanatic
Re: How do you determine the correct pushrod length? Also, if this guy that did your heads indeed sunk a valve too deep, the "Installed Height" on that valve would be way off, and the only way to correct the intalled height problem would be to install a shim / spacer under that valve spring to get the installed height back to a proper dimension.
Unless he really screwed up your valve job, I still believe you have a collapsed lifter.
If the lifter are ok, I would be making the guy that screwed up your $$$$ heads buy you a new set before I would run various length pushrods in the motor just to fix his poor work.
Good Luck,
Ron
Unless he really screwed up your valve job, I still believe you have a collapsed lifter.
If the lifter are ok, I would be making the guy that screwed up your $$$$ heads buy you a new set before I would run various length pushrods in the motor just to fix his poor work.
Good Luck,
Ron
07-23-2002, 01:40 AM
#4
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Re: How do you determine the correct pushrod length? </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by 2001WS6Vert:
<strong>I just built my motor, LS6 block, 6.0 heads. After it started I had a miss. I found it to be an exhaust valve staying open all the time. If I loosened the rocker I got my compression back. I called the guy that did the heads and he said to use .025 shorter pushrods which I did. It runs O.K. now but clatters. It sounds like it could be from one or two cylinders. I want to know how to determine exact pushrod length that I will need. It sounds like to get it quiet I might have to use different lengths on different cylinders (maybe some irregularities on the valve job). I talked to one guy who said that you tighten the rocker until there is no slack and then count the turns until it is tight. How many turns should that be? I can't stand the way this new engine sounds. Thanks</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Kinda sounds like you may have set the valves too tight. After you get no slack or the(no longer moves up and down) you only need to turn another 1/4 - 1 turn. If you turn util they are tight, you could end up going 2-3+ turns which will be toooo tight.
If you do them too tight, I think the valves will not close all the way, and you will not get much compression. The car will miss, or not idle at all depending on how may cylinders have the valves set too tight. And the car will sound funny, not too mention loose power.
Also all the cylinders lash (valves) should be set the same.
Set your valves agian , and dont go too tight.
1/4 - 1 turn after full lash would probably be good to make sure they are not to tight. We do it while the engine is running , that way you can hear the pitch of the engine change as you adjust them. If they are set while the engine is running you will see what i mean by what happens if they are set to tight.
<strong>I just built my motor, LS6 block, 6.0 heads. After it started I had a miss. I found it to be an exhaust valve staying open all the time. If I loosened the rocker I got my compression back. I called the guy that did the heads and he said to use .025 shorter pushrods which I did. It runs O.K. now but clatters. It sounds like it could be from one or two cylinders. I want to know how to determine exact pushrod length that I will need. It sounds like to get it quiet I might have to use different lengths on different cylinders (maybe some irregularities on the valve job). I talked to one guy who said that you tighten the rocker until there is no slack and then count the turns until it is tight. How many turns should that be? I can't stand the way this new engine sounds. Thanks</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Kinda sounds like you may have set the valves too tight. After you get no slack or the(no longer moves up and down) you only need to turn another 1/4 - 1 turn. If you turn util they are tight, you could end up going 2-3+ turns which will be toooo tight.
If you do them too tight, I think the valves will not close all the way, and you will not get much compression. The car will miss, or not idle at all depending on how may cylinders have the valves set too tight. And the car will sound funny, not too mention loose power.
Also all the cylinders lash (valves) should be set the same.
Set your valves agian , and dont go too tight.
1/4 - 1 turn after full lash would probably be good to make sure they are not to tight. We do it while the engine is running , that way you can hear the pitch of the engine change as you adjust them. If they are set while the engine is running you will see what i mean by what happens if they are set to tight.
07-23-2002, 08:04 AM
#5
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Thread Starter
Re: How do you determine the correct pushrod length? RPM2800, The rockers are not adjustable on the LS1 like they were on the old small blocks (I wish they were though). I see that some vendors do sell adjustable rocker setups. I might just get one of those and see if it helps instead of installing different pushrods until I get it right. The guy I talked to said that you should get about two turns out of the rocker bolts after the pushrods become tight. Maybe i'm chasing a ghost, maybe its in the forged pistons. This car is so difficult to work on I wish I'd just hot rodded my 79 El Camino instead.
