Pushrod question!
10-01-2012, 11:31 PM
#1
Pushrod question! Hey guys I know a guy selling a set of push rods for 40 bucks never used just wondering if the specs sound correct I have stock heads running a 228R comp cam Ls 7 lifters. I've spoken with people and they said the 7.4 pushrod will work with my center but I'm clueless when it comes to the other specs so just tell me if they look correct it's a 5.3 motor
Set of 16, 5/16 Dia. .080 wall pushrodsFor LS1,LS2,LS6 and othersCompair to Comp Cams No. 7955-16 never used
Set of 16, 5/16 Dia. .080 wall pushrodsFor LS1,LS2,LS6 and othersCompair to Comp Cams No. 7955-16 never used
10-02-2012, 12:42 AM
#2
What head gasket? Graphite or MLS? Either way, MOST aftermarket cams have a smaller base circle, so all things being the same, you should "usually" need a 7.425 but the only way to know is to CHECK.
EO/IC Method is what I use.
From Shane at Thunder Racing.
The TDC method is NOT always accurate. Try the EO/IC method to check pushrod length. I have posted directions on this forum numerous times... Here it is again:
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!!!
Check it using the above method and see where you are.
Thanks,
Shane
EO/IC Method is what I use.
From Shane at Thunder Racing.
The TDC method is NOT always accurate. Try the EO/IC method to check pushrod length. I have posted directions on this forum numerous times... Here it is again:
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!!!
Check it using the above method and see where you are.
Thanks,
Shane
10-02-2012, 01:57 AM
#4
Shane told me the ideal preload on an LS7 lifter to avoid the most noise is 1 full turn from zero lash. He's ran them with .010 all the way to .120 and the only thing that changed was sound, not an ounce of power on the dyno.
I myself went to 1 full turn from zero lash to 22ft lbs and it runs great so far.
That write up by shane though was prob the easiest way in the world of explaining something I've ever read. I didn't even use the damned checker.
@ .588 lift you very well may NOT have a smaller base circle on the cam. All you can do to be absolutely sure is throw the stock PR's in cylinder #1 and use the EO/IC method to get zero lash, and count the # of turns to 22ft lbs.
Oh, and My AFR's @ 59cc and a GM MLS head gasket netted me a 7.4 PR on the money.
I myself went to 1 full turn from zero lash to 22ft lbs and it runs great so far.
That write up by shane though was prob the easiest way in the world of explaining something I've ever read. I didn't even use the damned checker.
@ .588 lift you very well may NOT have a smaller base circle on the cam. All you can do to be absolutely sure is throw the stock PR's in cylinder #1 and use the EO/IC method to get zero lash, and count the # of turns to 22ft lbs.
Oh, and My AFR's @ 59cc and a GM MLS head gasket netted me a 7.4 PR on the money.
06-21-2013, 02:38 AM
#6
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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.
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.
I appreciate this simple method you have come up with for preload checking. I am not so sure about the math behind it though.
The rocker bolt is a 8mm bolt with 1.25mm thread pitch. So one complete turn amounts to 1.25mm (or 0.0492"). That is 0.0492" at the rocker bolt.
But isn't the travel at the pushrod then increased due to the rocker ratio? Rocker is 1:1.7 ratio. The valve end stays fixed so if the bolt moves 1.25mm then the pushrod would move 1.25mm x 2.7/1.7 = 1.985mm = 0.0782".
Did you estabish the 0.047" preload per turn through measurement or calculation?
I get 0.078" per turn with my math, which is a big difference. Feel free to correct me if my math is wrong.
Jeremy
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06-21-2013, 06:57 AM
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Not Shane? Whatever.
It seems like a lot of people in the forums are just spouting what others have said as gospel. Once it gets repeated 3 times then really becomes gospel. I guess it could have been the words of Shane from Thunder Racing?
The method makes sense but the stated preloads don't. I guess the question is, has anybody actually measured the lifter preload using the method given in this post and verified the results?? It seems like a good way to go about checking preload.....if the results are correct!
It seems like a lot of people in the forums are just spouting what others have said as gospel. Once it gets repeated 3 times then really becomes gospel. I guess it could have been the words of Shane from Thunder Racing?
The method makes sense but the stated preloads don't. I guess the question is, has anybody actually measured the lifter preload using the method given in this post and verified the results?? It seems like a good way to go about checking preload.....if the results are correct!
06-21-2013, 09:48 AM
#9
Not Shane? Whatever.
It seems like a lot of people in the forums are just spouting what others have said as gospel. Once it gets repeated 3 times then really becomes gospel. I guess it could have been the words of Shane from Thunder Racing?
The method makes sense but the stated preloads don't. I guess the question is, has anybody actually measured the lifter preload using the method given in this post and verified the results?? It seems like a good way to go about checking preload.....if the results are correct!
It seems like a lot of people in the forums are just spouting what others have said as gospel. Once it gets repeated 3 times then really becomes gospel. I guess it could have been the words of Shane from Thunder Racing?
The method makes sense but the stated preloads don't. I guess the question is, has anybody actually measured the lifter preload using the method given in this post and verified the results?? It seems like a good way to go about checking preload.....if the results are correct!
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