Lifter preload and pushrod length frustrations
08-23-2015, 10:37 PM
#1
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Lifter preload and pushrod length frustrations alright so i have a PRC head and Johnson link bar lifter set up that is finally coming together. I have a question that i am hoping someone can help me with. i used the comp checker and got 16.25-16.37 turns.. i checked for base circle with the adjustable checker and a dial indicator. i rotated the motor to find the highest point of the cam and then waited for it to close/lower completely until the dial indicator was at its lowest point. This giving me the lowest point which i assume is the base circle. I then checked this with the IO/EC method. So i came up with 16.37 x.050+6.8+.032=7.650 pushrod length for .032 preload. I did this on cylinders 1,3,5,7 and averaged them all (turns were between 16.25-16.37) So i orders 7.647 pushrods. So i put the motor backed together and found that i only had about .25 turns on the rocker bolt from pushrod to rocker cup contact. I read a thread stating 1 full turn on the rocker bolt is .047 in lenght. With that said i am concerned that my pushrods aren't long enough? I dont have any lash on the rockers but when on the base circle the rocker tips are easy to move left to right but has no lash... I know no one can wave a magic wand and diagnose or measure this for me but just looking for opinions. Can i hurt the motor with less pushrod than desirable? i know it might be noisy and that will tell me if my measurements are wrong. If the 1 full turn method is correct and i only had .25 turns until the rocker seated then i have .011 preload putting me .019 short of the required .030 minimum johnson provided. (.047 /4 =.011 =1/4 turn) Thanks in advance
Matt
Matt
08-23-2015, 11:24 PM
#2
How did you get 16.37 turns? It was hard enough to know .25 or .5 with the piece of junk Comp adjustable pushrod.
Best way to do it is to put some tape on the thread of the adjustable rocker, set it, and then torque the rocker down after you measure to see. That gives you your check. But basically, if you are at 16.25 turns @ .050 + 6.8 = 7.615" + preload. No need to check it if you're on the base circle. Zero lash means you tighten down the bolt just enough to get rid of the up and down slop, but you don't preload the bolt at all. If you did that 7.645" would be the right length regardless of what the rocker bolt turns says.
Best way to do it is to put some tape on the thread of the adjustable rocker, set it, and then torque the rocker down after you measure to see. That gives you your check. But basically, if you are at 16.25 turns @ .050 + 6.8 = 7.615" + preload. No need to check it if you're on the base circle. Zero lash means you tighten down the bolt just enough to get rid of the up and down slop, but you don't preload the bolt at all. If you did that 7.645" would be the right length regardless of what the rocker bolt turns says.
08-24-2015, 07:29 AM
#3
Well, this will help a little. Your calculation doesn't take into account the rocker ratio from the bolt so you can't just ratio off of the 0.047" value. Here is what I get:
0.25 turns X 1.25 mm/turn = 0.3125 mm
0.3125 mm / 25.4 mm per inch = 0.0123 inches
This value is the movement of the bolt, not the tip of the rocker where the pushrod is. The obtain the pushrod movement, you have to use parallel triangles:
0.0123 inches X (2.7/1.7) = 0.019 inches
If you have the dial indicator, back off on the rocker bolt and set the dial indicator in line with the pushrod. Then tighten the bolt to zero lash. Set the dial to zero and then tighten. This will give you the most accurate preload value.
Also, you will get some side to side even with more preload, that is not an issue.
Here is a link to a long thread with diagrams where this is all discussed. Hope it helps. Link
0.25 turns X 1.25 mm/turn = 0.3125 mm
0.3125 mm / 25.4 mm per inch = 0.0123 inches
This value is the movement of the bolt, not the tip of the rocker where the pushrod is. The obtain the pushrod movement, you have to use parallel triangles:
0.0123 inches X (2.7/1.7) = 0.019 inches
If you have the dial indicator, back off on the rocker bolt and set the dial indicator in line with the pushrod. Then tighten the bolt to zero lash. Set the dial to zero and then tighten. This will give you the most accurate preload value.
Also, you will get some side to side even with more preload, that is not an issue.
Here is a link to a long thread with diagrams where this is all discussed. Hope it helps. Link
08-24-2015, 09:40 AM
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Thanks for the reply guys. I used a small rubber band on the the adjustable pushrod on order to hold it in place. it was over 16.25 but under 16.5 so i am confident with that. I am not confident i have achieved the .030 required especially after your reply. Will i hurt this thing if i start it with the lesser preload? i know it may make some noise. I am just in the air on it as i measured 4 cylinders and both lobes on each. I am confident in the measurements i took. the only part that concerned me was the thread that stated one full turn was .047. i don't mean to beat a dead subject and have researched a ton. Thank you for your reply's and time!
08-24-2015, 11:01 AM
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I highly recommend using a caliper to measure the length at zero lash and zero preload. Takes all the guess work out. I borrowed one from work to take the measurements
08-26-2015, 10:12 PM
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that is what i am going to do. i have one comp trunion kit that didnt feel right and have a new one on the way. i am going to use the dial indicator to measure. to be honest i never thought of it. thanks for all the help guys!
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09-07-2015, 09:55 PM
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alright guys quick update on my issue. I did use a dial indicator to figure out what i had and found that the lowest preload was at .009 and the most i had was at .015. keep in mind it is difficult to do this in an F-Body so these measurements are close. So i went a step further and used the adjustable push rod to find desired pushrod length/preload. I found that i needed 17 turns complete. The math says it should be 17 x .050 + 6.8 = 7.65. This is .003 more than i ordered and i have the measured preload as stated. So with that said i bought a caliper and found the JUNK comp checker is not .050 each turn. I found at 17 turns total length is 7.665. This is .015 longer than everyone claims. With that said it would put me right at the .030 i though i measured originally. Frustrating to say the least but i am glad i figured it out. At 17 turns i found i was anywhere between .029 and .039 on different lobes. So another 200 dollars down the drain. With that said i also measured my Manton pushrod and found that they were short .006 from ordered spec. The did state that they had a .006 tolerance but figured they would have been closer. I will update the post at the end of the week when i get the new pushrods and hopefully start the car! 
09-08-2015, 06:02 AM
#9
Manton uses overall lengths for their measurement whereas Trend uses gauge length and Trend makes the pushrods for a lot of companies including Comp.
09-08-2015, 12:14 PM
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So this is gonna sound silly, im a very obvious person though. If an LS7 lifter takes preload of .030 to .120 right (guesstimate)? What the crap are we moaning about .00x differences?
09-08-2015, 12:42 PM
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I think the OP is using Johnson lifters. Much more precision needed on the preload
09-08-2015, 01:28 PM
#13
depends on which ones he's using. the 2116 link bars have a travel of ~.093 and Randy recommends that the preload is in the .035-.045 range. The short travel link bars have a travel of .053 and I honestly dont know what the recommended preload is.More info is needed from the op to proceed.
09-08-2015, 02:35 PM
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If it's the 2126's, the number is .038", which is a half turn from zero lash
09-08-2015, 04:30 PM
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thats correct i am using the johnson 2216lsr. johnson recommended .030-.040. its been a learning experiance to say the least! i am hoping to start the car this weekend. didnt know the difference between gauge length and overall lenght. so if anyone needs some manton 7.647 pushrods 5/16 .118 wall let me know
09-08-2015, 04:58 PM
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thats correct i am using the johnson 2216lsr. johnson recommended .030-.040. its been a learning experiance to say the least! i am hoping to start the car this weekend. didnt know the difference between gauge length and overall lenght. so if anyone needs some manton 7.647 pushrods 5/16 .118 wall let me know
09-09-2015, 02:59 PM
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Since this is relavent here I will disband shane at TRs way of measuring the bolt. I used this method that has become very well quoted here. Here's what I came up with: I measured his way, of turns at the bolt, each one supposed to equal 47 actual dialed in at near 80 at the pushrod. Thats a huge ******* difference. I did this on the table, with a fresh head, valve springs, rockers, and a dial indicator. Now I have to go back in every thread where I backed his method and fix my responses so future surfers dont use this incorrect info. Vettenuts always said it wasnt true, I checked myself, my hats off to you sir!
09-09-2015, 04:27 PM
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Since this is relavent here I will disband shane at TRs way of measuring the bolt. I used this method that has become very well quoted here. Here's what I came up with: I measured his way, of turns at the bolt, each one supposed to equal 47 actual dialed in at near 80 at the pushrod. Thats a huge difference. I did this on the table, with a fresh head, valve springs, rockers, and a dial indicator. Now I have to go back in every thread where I backed his method and fix my responses so future surfers dont use this incorrect info. Vettenuts always said it wasnt true, I checked myself, my hats off to you sir!