pushrod length with cam
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From: Morristown, Tn
pushrod length with cam I know, I know, it's a tired subject. I'm putting a texas speed torquerv2 into a running LS6. I think the cam is 232/234 and just under .600 lift. The engine has 34k since a rebuild was done, I bought it with zero miles after the build and ran it until now. I was told that the heads were milled 30 thousandths. Lifters are stock to my knowledge.
My dumb *** didn't think to compare base circles of the stock cam and the new cam before I installed it.
Ive installed the new cam and Ive read up on the PR checking procedure and done a lot of the testing/checking with my comp pushrod checker. I'm having texas speed send my pushrods that came with the cam package as soon as I settle on a size.
I initially did some measuring and determined that a 7.425 would probably work, so thats what I mentioned to texas speed, and they replied:
So I gave this another try.
I put a pushrod in the exhaust side of the cylinder I'm checking, installed the rocker, and turned the crank until the exhaust valve opened. Then I moved the pushrod and rocker to the same cyl's intake valve. I used a different cyl. for this test than the one I was using in the first test, just in case there was something wierd with the lifter on that cyl.
I set my checker pushrod to 7.4 length. I turned the rocker bolt by hand until I could no longer move the rocker up/down (tink/tink/tink) off of the valve stem. Then I torqued the rocker bolt from that point. I got 1.4 turns.
I repeated the procedure with the checker set to 7.425, and got 1.8 turns.
I repeated the procedure with the checker set to 7.375, and got 0.8 turns.
Just for good measure. I shortened the checker and put it into the intake side so it was loose, and torqued the rocker down. Then I lengthened the checker by hand while in the engine, until again I could no longer move the rocker up and down on the valve stem. I took it out and counted the turns and it worked out to 7.325 at zero lash with no preload. So that would seem to indicate that .075 preload would give me 7.4", or 0.100 preload would give me 7.425.
What do you think? 7.4 or 7.425?
My dumb *** didn't think to compare base circles of the stock cam and the new cam before I installed it.
Ive installed the new cam and Ive read up on the PR checking procedure and done a lot of the testing/checking with my comp pushrod checker. I'm having texas speed send my pushrods that came with the cam package as soon as I settle on a size.
I initially did some measuring and determined that a 7.425 would probably work, so thats what I mentioned to texas speed, and they replied:
Originally Posted by Jon@Texas-Speed
That still seems a little long. I would think something like a 7.375" max. Try checking it with the rocker torqued down and backing the checker out until you are at zero lash and see what it measures.
That still seems a little long. I would think something like a 7.375" max. Try checking it with the rocker torqued down and backing the checker out until you are at zero lash and see what it measures.
I put a pushrod in the exhaust side of the cylinder I'm checking, installed the rocker, and turned the crank until the exhaust valve opened. Then I moved the pushrod and rocker to the same cyl's intake valve. I used a different cyl. for this test than the one I was using in the first test, just in case there was something wierd with the lifter on that cyl.
I set my checker pushrod to 7.4 length. I turned the rocker bolt by hand until I could no longer move the rocker up/down (tink/tink/tink) off of the valve stem. Then I torqued the rocker bolt from that point. I got 1.4 turns.
I repeated the procedure with the checker set to 7.425, and got 1.8 turns.
I repeated the procedure with the checker set to 7.375, and got 0.8 turns.
Just for good measure. I shortened the checker and put it into the intake side so it was loose, and torqued the rocker down. Then I lengthened the checker by hand while in the engine, until again I could no longer move the rocker up and down on the valve stem. I took it out and counted the turns and it worked out to 7.325 at zero lash with no preload. So that would seem to indicate that .075 preload would give me 7.4", or 0.100 preload would give me 7.425.
What do you think? 7.4 or 7.425?
Joined: Aug 2007
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From: Turnin' Wrenches Infractions: 005
Even though i have done this several times I still find myself checking several times till I get repeatable results. I like to see the exact same outcome several times in a row before I commit to a pushrod order. This is the method I have always used:
FWIW, EVERY cam install I have done using the LS7 lifter with a cam with greater than .600" lift (read smaller base circle) AND stock heads w/GM MLS gaskets has taken 7.425" pushrods for ~.050"-.060" preload. We measure lifter preload on each and every cam install we do. I have never had a lifter failure nor do we end up with the dreaded "sewing machine" noise.
Its very simple, If you change ANY of the following:
valve sizes, valve job, head milling, thinner/thicker head gaskets, decked block, cam with an altered base circle, etc... YOU MUST CHECK FOR PROPER PUSHROD LENGTH.
I have helped countless numbers of individuals with this process over the phone, via email, and PM's. I've posted the process on at least 3 occasions.
Here it is again in a nutshell:
1. Using the EO/IC method, get the lifter to the base circle of the cam.
2. Using a known length pushrod (7.400" is a good start with stock rockers) run the rocker arm bolt down to zero lash. This is easily done with your fingers "wiggling" the rocker, the point at which the "slack" is just gone is zero lash.
3. Set your torque wrench to 22 lb./ft. Tighten the rocker to full torque and count the number of turns it takes to get there. 1 full turn wtih a stock 8mm X 1.25 bolt is ~.047" preload as measured at the pushrod/rocker interface.
4. I normally shoot for 1 1/4 to 1 3/4 turns with stock type lifters like Comp 850's, LS1, LS7 etc.
For an example, if you use a 7.400" pushrod and come up with 3/4 of a turn, you will need at least .025" longer pushrod to get into range. If you end up with 2 1/4 turns, you will need one .025" shorter...
I might not know everything but I will tell you that this method has worked for me year after year cam swap after cam swap. We average 3 cam swaps a week here so you can do the math.
If you are not familiar with the EO/IC method for determining valve events in a 4 stroke engine, its very simple:
For a given cylinder as the Exhaust valve is Opening, the intake lifter will be on the base circle of the cam and lash/preload should be checked for that intake valve.
For a given cylinder as the Intake valve is Closing, the exhaust lifter will be on the base circle of the cam and lash/preload should be checked for that exhaust valve.
THIS METHOD ALWAYS WORKS!!!
I hope this helps someone. I have explained it so many times I think I do it in my sleep!!!
Shane
Its very simple, If you change ANY of the following:
valve sizes, valve job, head milling, thinner/thicker head gaskets, decked block, cam with an altered base circle, etc... YOU MUST CHECK FOR PROPER PUSHROD LENGTH.
I have helped countless numbers of individuals with this process over the phone, via email, and PM's. I've posted the process on at least 3 occasions.
Here it is again in a nutshell:
1. Using the EO/IC method, get the lifter to the base circle of the cam.
2. Using a known length pushrod (7.400" is a good start with stock rockers) run the rocker arm bolt down to zero lash. This is easily done with your fingers "wiggling" the rocker, the point at which the "slack" is just gone is zero lash.
3. Set your torque wrench to 22 lb./ft. Tighten the rocker to full torque and count the number of turns it takes to get there. 1 full turn wtih a stock 8mm X 1.25 bolt is ~.047" preload as measured at the pushrod/rocker interface.
4. I normally shoot for 1 1/4 to 1 3/4 turns with stock type lifters like Comp 850's, LS1, LS7 etc.
For an example, if you use a 7.400" pushrod and come up with 3/4 of a turn, you will need at least .025" longer pushrod to get into range. If you end up with 2 1/4 turns, you will need one .025" shorter...
I might not know everything but I will tell you that this method has worked for me year after year cam swap after cam swap. We average 3 cam swaps a week here so you can do the math.
If you are not familiar with the EO/IC method for determining valve events in a 4 stroke engine, its very simple:
For a given cylinder as the Exhaust valve is Opening, the intake lifter will be on the base circle of the cam and lash/preload should be checked for that intake valve.
For a given cylinder as the Intake valve is Closing, the exhaust lifter will be on the base circle of the cam and lash/preload should be checked for that exhaust valve.
THIS METHOD ALWAYS WORKS!!!
I hope this helps someone. I have explained it so many times I think I do it in my sleep!!!
Shane
this is how i did mine and every book i have read from lsx builders and ppl iv talked ot that build these motor all said i did it right. i all so trippled checked it. i went with .050 on preload as everyone told me it better to be a little light than too tight on the pre load.
set the timing marks at 12 o'clock to get the lifters on the base cr for number 1 cylinder then i took my comp cams push rod checker and turned it out 10 turns for a 7.3 length installed it and snugged down the rocker arm and watched it push in the push rod checker so i knew that wasn't zero lash. so i took everything back out turned in the checker half a turn witch should be 7.275. reinstalled it and the rocker and it got me zero lash. no up and down movement in rocker and the checker did have no preload on lifter here. so i then added .050 for the preload and came up with 7.325
set the timing marks at 12 o'clock to get the lifters on the base cr for number 1 cylinder then i took my comp cams push rod checker and turned it out 10 turns for a 7.3 length installed it and snugged down the rocker arm and watched it push in the push rod checker so i knew that wasn't zero lash. so i took everything back out turned in the checker half a turn witch should be 7.275. reinstalled it and the rocker and it got me zero lash. no up and down movement in rocker and the checker did have no preload on lifter here. so i then added .050 for the preload and came up with 7.325
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TECH Apprentice
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From: Morristown, Tn
That's the method I used in the first two tests.
Thread Starter
TECH Apprentice
iTrader: (25)
Joined: Feb 2007
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From: Morristown, Tn
On a related note, texas speed has failed to respond to my PM's sent about confirming PR length and getting my pushrods that were part of my cam kit sent out to me, for about a week now.
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Thread Starter
TECH Apprentice
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From: Morristown, Tn
This is the first I've heard of this while using stock rockers? None of the PR length checking writeups I've read have mentioned the need for this with stock rockers. Please, elaborate.
Thread Starter
TECH Apprentice
iTrader: (25)
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From: Morristown, Tn
No. Seeing as how they are a sponsor of this forum, this very section, posted the sale on this forum, the transaction was conducted on this forum via pm...why should I have to call them? Is that not what the PM system is for? The guy was showing online when I sent both pm's over the last week+.
Last edited by RotaryResurrection; Dec 18, 2010 at 11:15 PM.
sounds like Mez is talking about roller rockers not stockers
yea there isnt much u can do about the wipe pattern with stock rockers. And there is no reason to get snappy with me i was just saying. some time the phone works better.
