Checking for pushrod length? I'm not getting it
Checking for pushrod length? I'm not getting it Ok so here is what someone posted on here that knows there stuff (Shane@TR)
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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__________________________________________________ __________________________________________________ _
So my question is why would you want a .025 bigger pushrod if you got 3/4 turn on a 7.4 pushrod? Wouldn't you want a smaller pushrod to get get 1/2-3/4 more turn?
__________________________________________________ __________________________________________________ ______________________
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__________________________________________________ __________________________________________________ _
So my question is why would you want a .025 bigger pushrod if you got 3/4 turn on a 7.4 pushrod? Wouldn't you want a smaller pushrod to get get 1/2-3/4 more turn?
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From: Turnin' Wrenches Infractions: 005
What you are doing is loading the lifter. So in the example (remember one turn is about .050 preload). If you only get 3/4 from 0 lash to 22 ft/lbs, you have loaded your lifter around .035 to .040. You can't go anymore because the rocker is as tight as it will go. The bolt turning is downward motion being pushed in the lifter cup. Same example, you bump your adjustable pushrod .050, now it will catch "0 lash" with more bolt threads exposed, so this time you will get about 1 3/4 of a turn of bolts threads which = about .080 or so being pushed down in the lifter cup until the rocker is seated. You have achieved your preload.
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That's the key to understanding this method. The longer the pushrod is, the more turns you will get on the rocker bolt when starting from a "zero lash" condition to when the rocker bolt is at 22 ft-lbs.
Thanks guys. I was thinking it was something like that, just wanted to double check. I bet the biggest mistake people make when using this method is not getting zero lash right. What do you guys see as "zero lash"? I have always thought the best way is when there is no more up and down movement?
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From: Turnin' Wrenches Infractions: 005
Yep, that's what I do. I have noticed that there is still a little lateral side to side movement at zero lash. If you adjust till all movement is gone, it makes your readings a lot different.
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In the write-up it says:
"1 full turn with a stock 8mm X 1.25 bolt is ~.047" preload as measured at the pushrod/rocker interface."
FYI ... just to be more accurate, a 1.25 mm pitch metric bolt should actually move 0.049" for every turn.
There's 25.4 mm per inch ... so (1.25 mm)/(25.4 mm/in) = 0.0492"
"1 full turn with a stock 8mm X 1.25 bolt is ~.047" preload as measured at the pushrod/rocker interface."
FYI ... just to be more accurate, a 1.25 mm pitch metric bolt should actually move 0.049" for every turn.
There's 25.4 mm per inch ... so (1.25 mm)/(25.4 mm/in) = 0.0492"
Last edited by ZeeOSix; Sep 27, 2011 at 11:42 PM.
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Ahhh ... good point. Maybe he put the dial indicator on the tip of the rocker arm above the pushrod. That would probably be the best way to measure the actual distance the pushrod travels into the lifter as the rocker arm is tightened.
Also after you check a lifter a few times it forces the oil out of and makes it a little more difficult to find zero lash. Also watch the nose of the rocker where the pushrod is, you will be able to see when it starts to move the pushrod down. Doing both of these things will help you get a "feel" of where zero lash is and what it feels like.
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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.
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.
Launching!
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From: Sierra Mountains and Stockton Ca.
Ok im in the middle of putting my engine back together and i was trying to see if my stock pushrods will work with my setup....... im not understanding one thing though.....how are you guys watching rocker movement to see eo/ic if they are loose? do you tighten them all in sequence to 22lbs? then loosen the rocker on the valve that you want to check the pushrod lenth on and watch its companion valve to see what its doing? then get zero lash for that valve and then count turns to check preload? im confused......is that rite?
this is where im at now.....all my rockers are loose and and the #1 cylinder is at tdc. i wanted to check the pushrod lenth before i tighten them all down. the intake valve on cylinder #1 in closed so its at base circle of the cam rite? when i tighten the rocker so the pushrod was at zero lash it was nowhere near even having the rocker seating on the mounting bracket that the rockers sit in......i had to tighten the rocker bolt like 5 or 6 more turns to get it to seat snug. so i know somethings wrong, im not doing something rite.
this is where im at now.....all my rockers are loose and and the #1 cylinder is at tdc. i wanted to check the pushrod lenth before i tighten them all down. the intake valve on cylinder #1 in closed so its at base circle of the cam rite? when i tighten the rocker so the pushrod was at zero lash it was nowhere near even having the rocker seating on the mounting bracket that the rockers sit in......i had to tighten the rocker bolt like 5 or 6 more turns to get it to seat snug. so i know somethings wrong, im not doing something rite.
Last edited by ggino85; Sep 30, 2011 at 01:16 PM.
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this is where im at now.....all my rockers are loose and and the #1 cylinder is at tdc. i wanted to check the pushrod lenth before i tighten them all down. the intake valve on cylinder #1 in closed so its at base circle of the cam rite? when i tighten the rocker so the pushrod was at zero lash it was nowhere near even having the rocker seating on the mounting bracket that the rockers sit in......i had to tighten the rocker bolt like 5 or 6 more turns to get it to seat snug. so i know somethings wrong, im not doing something rite.
Or try this:
Another way to get on the base circle directly opposite the cam lobe peak is to turn the engine until the rocker arm is all the way down (ie, valve all the way open). Mark the crank pulley (piece of tape), and then turn the crankshaft 1 full turn from that point. This will turn the cam 1/2 turn, and put the lifter 180 degrees opposite the cam lobe, and in about the center of the base circle range between cam ramps.
Last edited by ZeeOSix; Sep 30, 2011 at 02:21 PM.
Ok im in the middle of putting my engine back together and i was trying to see if my stock pushrods will work with my setup....... im not understanding one thing though.....how are you guys watching rocker movement to see eo/ic if they are loose? do you tighten them all in sequence to 22lbs? then loosen the rocker on the valve that you want to check the pushrod lenth on and watch its companion valve to see what its doing? then get zero lash for that valve and then count turns to check preload? im confused......is that rite?
this is where im at now.....all my rockers are loose and and the #1 cylinder is at tdc. i wanted to check the pushrod lenth before i tighten them all down. the intake valve on cylinder #1 in closed so its at base circle of the cam rite? when i tighten the rocker so the pushrod was at zero lash it was nowhere near even having the rocker seating on the mount that the rockers sit in......i had to tighten the rocker bolt like 5 or 6 more turns to get it to seat snug. so i know somethings wrong, im not doing something rite.
this is where im at now.....all my rockers are loose and and the #1 cylinder is at tdc. i wanted to check the pushrod lenth before i tighten them all down. the intake valve on cylinder #1 in closed so its at base circle of the cam rite? when i tighten the rocker so the pushrod was at zero lash it was nowhere near even having the rocker seating on the mount that the rockers sit in......i had to tighten the rocker bolt like 5 or 6 more turns to get it to seat snug. so i know somethings wrong, im not doing something rite.
Launching!
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From: Sierra Mountains and Stockton Ca.
ok well i did goof a little, it was the #2 cylinder that was at tdc, thats the cylinder i was checking so i dont think it makes a difference. i know that cylinder is at tdc for sure because i put it there rite before i put my heads on. anyone else have any tips.
zee0six, when you say keep turning until it is at tdc, how will i know when its at tdc?
sorry if i sound like a total goof, this has just really messed with me. i though i understood it but when i went out to actually do it, i didnt get it at all. lol.
im kind of getting it. my first check was 2 and 1/4 turn from zero lash to 22 ft lbs....im going to check another pushrod rite now. thats way too much preload for ls7 lifters if thats what it turns out to be, correct?
zee0six, when you say keep turning until it is at tdc, how will i know when its at tdc?
sorry if i sound like a total goof, this has just really messed with me. i though i understood it but when i went out to actually do it, i didnt get it at all. lol.
im kind of getting it. my first check was 2 and 1/4 turn from zero lash to 22 ft lbs....im going to check another pushrod rite now. thats way too much preload for ls7 lifters if thats what it turns out to be, correct?
Last edited by ggino85; Sep 30, 2011 at 06:36 PM.