pushrod length questions
pushrod length questions based on the below..
i just got my heads reworked, new stroker block, new lifters.
i did below. making sure the rocker was able to be wiggled and tq'd the oem bolt down to 22 lb ft. i was only able to get 1/2 a turn
consistently
now.
i am off be 3/4 - 1 1/4 turn off.
would 7.425 be sufficient or should i try for a little bit longer
Originally Posted by XtraCajunSS
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_______________________________
i just got my heads reworked, new stroker block, new lifters.
i did below. making sure the rocker was able to be wiggled and tq'd the oem bolt down to 22 lb ft. i was only able to get 1/2 a turn
consistently
now.
i am off be 3/4 - 1 1/4 turn off.
would 7.425 be sufficient or should i try for a little bit longer
Originally Posted by XtraCajunSS
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_______________________________
It depends on what lifters* your using. If your using stock or ls7 lifters you will want 1 1/4-1 3/4 turns to get the right preload on the lifter. My question is how are you determining zero lash? If you don't get very close to zero lash your measurements will be completely off.
Last edited by z99ls1; Oct 3, 2011 at 12:05 AM.
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It depends on what pushrods your using. If your using stock or ls7 lifters you will want 1 1/4-1 3/4 turns to get the right preload on the lifter. My question is how are you determining zero lash? If you don't get very close to zero lash your measurements will be completely off.
I did the "rocker arm bolt turns from zero lash" method tonight to see what my lifter pre-load was. What I found easy and repeatable to find zero lash was to simply turn the rocker arm bolt until the slightest resistance was felt. This was the zero lash point - no play at the rocker arm tip or at the pushrod. Then count number of turns from there until a torque of 22 ft-lbs was achieved.
I'd think it depends more on what lifters you're using, and what the total plunger travel is in the lifters. You try to get the right length pushrod to put the plunger near the center of the lifter's travel range.
I did the "rocker arm bolt turns from zero lash" method tonight to see what my lifter pre-load was. What I found easy and repeatable to find zero lash was to simply turn the rocker arm bolt until the slightest resistance was felt. This was the zero lash point - no play at the rocker arm tip or at the pushrod. Then count number of turns from there until a torque of 22 ft-lbs was achieved.
I did the "rocker arm bolt turns from zero lash" method tonight to see what my lifter pre-load was. What I found easy and repeatable to find zero lash was to simply turn the rocker arm bolt until the slightest resistance was felt. This was the zero lash point - no play at the rocker arm tip or at the pushrod. Then count number of turns from there until a torque of 22 ft-lbs was achieved.
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Verdad Gallardo I'm not really understanding how your doing it. Could you describe in more detail how your finding zero lash? You should spin the rocker when you just start to feel drag. Or when you lift on the rocker when there is no more "tick" noise".
Last edited by z99ls1; Oct 3, 2011 at 02:35 AM.
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0.035" longer pushrods to get 1-1/4 turns total.
0.047" longer pushrods to get 1-1/2 turns total.
0.059" longer pushrods to get 1-3/4 turns total.
How do you know what length pushrods you have right now?
Tightening the rocker arm bolt by a careful hand until there is no lash works fine ... you will feel the bolt start to resist ever so slightly when zero lash occurs. Seemed to work fine for me, and got repeatable numbers.
so i have 7.400 pushrods currently.
cam is tsunami
w/ ls7 lifters
the heads are prc ls6 that were milled .002
i double checked again with zero lash on bolt and was getting 1 3/4 turn.
when i did zero lash on bolt i validated that the bolt had just started resistance by turning the rocker and noticed it catched the bolt turning so i backed it off a smidge..
however when i do zero lash on bolt, the rocker is easily moved all over the place.
the way i was getting zero lash on the rocker was by wiggling the rocker till it started having resistance. and was getting 1/2 turn.
so at this point. what should i take into account or what can i do to validate?
cam is tsunami
w/ ls7 lifters
the heads are prc ls6 that were milled .002
i double checked again with zero lash on bolt and was getting 1 3/4 turn.
when i did zero lash on bolt i validated that the bolt had just started resistance by turning the rocker and noticed it catched the bolt turning so i backed it off a smidge..
however when i do zero lash on bolt, the rocker is easily moved all over the place.
the way i was getting zero lash on the rocker was by wiggling the rocker till it started having resistance. and was getting 1/2 turn.
so at this point. what should i take into account or what can i do to validate?
You can validate your measurement using an adjustable pushrod and the procedure shown in this post:
https://ls1tech.com/forums/7957678-post2.html
https://ls1tech.com/forums/7957678-post2.html
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so i have 7.400 pushrods currently.
cam is tsunami
w/ ls7 lifters
the heads are prc ls6 that were milled .002
i double checked again with zero lash on bolt and was getting 1 3/4 turn.
when i did zero lash on bolt i validated that the bolt had just started resistance by turning the rocker and noticed it catched the bolt turning so i backed it off a smidge..
however when i do zero lash on bolt, the rocker is easily moved all over the place.
the way i was getting zero lash on the rocker was by wiggling the rocker till it started having resistance. and was getting 1/2 turn.
so at this point. what should i take into account or what can i do to validate?
cam is tsunami
w/ ls7 lifters
the heads are prc ls6 that were milled .002
i double checked again with zero lash on bolt and was getting 1 3/4 turn.
when i did zero lash on bolt i validated that the bolt had just started resistance by turning the rocker and noticed it catched the bolt turning so i backed it off a smidge..
however when i do zero lash on bolt, the rocker is easily moved all over the place.
the way i was getting zero lash on the rocker was by wiggling the rocker till it started having resistance. and was getting 1/2 turn.
so at this point. what should i take into account or what can i do to validate?
I want to double check and make sure I'm right in the way I'm reading this. I have exactly one full turn from zero lash. Does this mean I need a 7.425?
The combo is a set of PRC 5.3's milled .030, Ls7 lifters, G5x3 cam, GM 5.7 MLS gaskets.
We started the engine last night with 7.400 pushrods and it has a ton of valve train noise.
The combo is a set of PRC 5.3's milled .030, Ls7 lifters, G5x3 cam, GM 5.7 MLS gaskets.
We started the engine last night with 7.400 pushrods and it has a ton of valve train noise.
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If you are getting 1 turn with 7.400" pushrods, then using 7.425" pushrods will give you 1-1/2 turns on the rocker bolt from zero lash.
First off how are you making sure you are on the base circle of the cam?
Second the more you check pushrod length on a lifter the harder it gets. When you tighten it down you are pushing oil out of the lifter and with the engine not running there is no way to fill it back up.
I ran into this when I was checking mine a while back. It is much harder to find zero lash with the lifter not being pumped up. Even at zero lash the rocker arm will have side to side movement especially if the lifter isn't pumped up.
I would suggest going to a different cylinder with fresh lifters if you have been using one cylinder for a while.
I'm seriously considering making a video on how to check pushrod length.
Second the more you check pushrod length on a lifter the harder it gets. When you tighten it down you are pushing oil out of the lifter and with the engine not running there is no way to fill it back up.
I ran into this when I was checking mine a while back. It is much harder to find zero lash with the lifter not being pumped up. Even at zero lash the rocker arm will have side to side movement especially if the lifter isn't pumped up.
I would suggest going to a different cylinder with fresh lifters if you have been using one cylinder for a while.
I'm seriously considering making a video on how to check pushrod length.
Quit trying to calculate lifter preload by turns on the rocker. The rockers are not that accurate to begin with. The best way (and only way IMO) is to use an adjustable pushrod. They are cheap. Buy a couple of good ones. Install the pushrod with it adjusted too short. Torque the rocker. then lengthen the push rod while spinning it. Once you feel drag, STOP. Remove the rocker, and measure the pushrod. Calculate how much depth you want in the lifter and and add it to the pushrod length. That's what you order. It's dead on accurate.
ok i have another question to add to this thread.
my shortblock has been rebuilt and i am torquing my heads down today. so obviously all valves are closed. i need to check my pushrod length and am a bit confused on how to. in my case would the correct way of doing this be to bolt up the rocker stand and arm with the pushrod length checker in place and tighten the rocker arm bolt down to zero lash. than open the pushrod length checker till it has some drag and the rocker can not move up and down by hand to create a tapping noise? or should i torque the rocker arm bolt to 22flbs and open the pushrod length checker till it has some drag and stop and that is my pushrod length?
my shortblock has been rebuilt and i am torquing my heads down today. so obviously all valves are closed. i need to check my pushrod length and am a bit confused on how to. in my case would the correct way of doing this be to bolt up the rocker stand and arm with the pushrod length checker in place and tighten the rocker arm bolt down to zero lash. than open the pushrod length checker till it has some drag and the rocker can not move up and down by hand to create a tapping noise? or should i torque the rocker arm bolt to 22flbs and open the pushrod length checker till it has some drag and stop and that is my pushrod length?
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Post #18 above pretty much described how to do it with an adjustable pushrod length checker.
Make sure you do the pushrod length check when the lifter is on the base circle of cam when doing the length check. See post #1 for details on making sure you're on the cam base circle using the EO/IC method. (EO/IC = Exhaust Opening/Intake Closing)
Make sure you do the pushrod length check when the lifter is on the base circle of cam when doing the length check. See post #1 for details on making sure you're on the cam base circle using the EO/IC method. (EO/IC = Exhaust Opening/Intake Closing)