Checked pushrod length... Now I'm really confused.
01-13-2012, 07:21 PM
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Checked pushrod length... Now I'm really confused. So I followed this writeup...
All made sense, went and done it and came up with 1/2 a turn on exhaust, 3/4 on intake which by the way that shows, I need either 7.425 or 7.450 pushrods.
I don't understand this because I have a 6.0, 317 heads milled .040 and a comp 228/232 .598 110 LSA cam. I understand with the cam the base circle will be a bit smaller, making me need a tad longer pushrod, but I figured the .040 off the heads would more than make up for that. Am I crazy?
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
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
I don't understand this because I have a 6.0, 317 heads milled .040 and a comp 228/232 .598 110 LSA cam. I understand with the cam the base circle will be a bit smaller, making me need a tad longer pushrod, but I figured the .040 off the heads would more than make up for that. Am I crazy?
01-13-2012, 08:11 PM
#4
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Yeah, that's what I was thinking. He seems to know his stuff from what I have read, and the concept makes total sense. I just don't get how I need longer (not shorter as I had guessed) pushrods.
01-14-2012, 01:33 AM
#7
get a 20 dollar pushrod length checker, figure out the length for 0 lash then add your preload. if you come up with the same amount then you were right in the first place. the adjustable pushrod method takes all of the question on how far you actually turned the bolt.
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01-14-2012, 02:46 AM
#10
So I followed this writeup...
.
.
.
All made sense, went and done it and came up with 1/2 a turn on exhaust, 3/4 on intake which by the way that shows, I need either 7.425 or 7.450 pushrods.
I don't understand this because I have a 6.0, 317 heads milled .040 and a comp 228/232 .598 110 LSA cam. I understand with the cam the base circle will be a bit smaller, making me need a tad longer pushrod, but I figured the .040 off the heads would more than make up for that. Am I crazy?
.
.
.
All made sense, went and done it and came up with 1/2 a turn on exhaust, 3/4 on intake which by the way that shows, I need either 7.425 or 7.450 pushrods.
I don't understand this because I have a 6.0, 317 heads milled .040 and a comp 228/232 .598 110 LSA cam. I understand with the cam the base circle will be a bit smaller, making me need a tad longer pushrod, but I figured the .040 off the heads would more than make up for that. Am I crazy?
01-14-2012, 07:58 AM
#11
There are a number of posts on how to measure. Shane's method approximates the length which is OK if you have the next size to check. If you are using it to buy pushrods, I prefer a direct measurement with an adjustable pushrod. I have verified his measurements with a dial indicator, but you can't just say 1 turn is 0.047" and 2 turns is twice that. It doesn't work that way as you need to account for bolt preload turns from zero lash and the rocker ratio.
With a 1/2 turn, the preload is approximately 0.013" and 3/4 turn is approximately 0.033".
With a 1/2 turn, the preload is approximately 0.013" and 3/4 turn is approximately 0.033".
01-14-2012, 08:12 AM
#12
I agree that is the right way I'm not disputing, I just read the part where he didn't use pushrods checker...that's how I've always seen it done correctly...relax I'm not saying anyone is wrong...damn u guys love to pounce like a lion if I don't fully explain myself, ****...I always thought best way was pushrods checker method using solid lifter and lighter checker valve springs (the real super thin ones)
But from you mods you should be "close", I agree with others saying to try another/all cylinders to get the best idea of what's going on..
But from you mods you should be "close", I agree with others saying to try another/all cylinders to get the best idea of what's going on..
01-14-2012, 10:42 AM
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Heading out right now to check a few other cylinders.
01-14-2012, 10:51 AM
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Oh, I just looked at what cam lobes I have, they are Comp Cams XE-R lobes, 3724 and 3726. How would I go about finding the base circle they use?
01-14-2012, 11:12 AM
#15
i tried to determine that on my Comp Cams xer lobed cam as well and i got a few different answers between ls1tech and Comp Cams tech line so really the only way is to mic the lobes (which is a lil hard to do with the cam installed)...
Do you have a pushrod length checker? did you use ls1 lifters or ls7 lifters? i know there will be a difference in pushrod length depending on the lifter used, as they use a different preload if im not mistaken...
Do you have a pushrod length checker? did you use ls1 lifters or ls7 lifters? i know there will be a difference in pushrod length depending on the lifter used, as they use a different preload if im not mistaken...
01-14-2012, 11:23 AM
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Thought I would throw a variable into the process... We were sweeping the valve train
to maximize lift on an engine project . Stocker Rules require a factory cam lift ie...515
So we burnt up some shims to space the rocker stands up to change lift. If any one needs
to adjust preload this is another quick way to help out that situation. We have the shims in
.035 and .005 ... give me a yell if interested...
[IMG]
[/IMG]
to maximize lift on an engine project . Stocker Rules require a factory cam lift ie...515
So we burnt up some shims to space the rocker stands up to change lift. If any one needs
to adjust preload this is another quick way to help out that situation. We have the shims in
.035 and .005 ... give me a yell if interested...
[IMG]
[/IMG]
01-14-2012, 11:55 AM
#17
I have verified his measurements with a dial indicator, but you can't just say 1 turn is 0.047" and 2 turns is twice that. It doesn't work that way as you need to account for bolt preload turns from zero lash and the rocker ratio.
With a 1/2 turn, the preload is approximately 0.013" and 3/4 turn is approximately 0.033".
With a 1/2 turn, the preload is approximately 0.013" and 3/4 turn is approximately 0.033".
Originally Posted by Shane
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.
01-14-2012, 01:26 PM
#18
In Shane's write-up, I thought it was verified that he used a dial indicator to come up with the "~0.047" per turn". I think I asked that question when I was doing pushrods, and someone came back saying he measured the with a dial-indicator at the pushrod/rocker interface (see red text in his quote below).
01-14-2012, 02:15 PM
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Okay, so I checked 6 cylinders and every one was between 1/3 and 2/3 turn on exhaust and 1/2-3/4 turn on intake. I am going to order 7.450 pushrods. Hope it works, lol.
01-15-2012, 01:54 PM
#20
Also, what lifters are you using? Different part number lifters have different plunger travel, and therefore different ideal pre-load settings.