lifter preload- check my calculations
05-22-2016, 02:41 AM
#1
lifter preload- check my calculations I had to change the top of my motor reciently. 317 heads milled to 65 cc,MLS Head gaskets, stock rockers with trunion mod. lunati cam 221/221 558/558 @114 . Gm Ls7 lifters. Anyway I put a couple pushrods in some of the cylinderheads(no rocker arms on the motor yet. I turned the motor over until I watched a given cylinders intake and exhaust pushrods go all the way down. I installed the lifter tray and installed the 2 rockers. Thightened them to zero lash with a 7.325 lenght pushrod and the pushrod bairly turned. I re-did the test with an adjustable pushrod set to 10 1/2 turns and they turned slightly. I did this on a couple of cylinders on both heads.
10 1/2 turns on the pushrod checker = 0.525 6.800 + 0.525 = 7.325 now add preload of 0.080 = 7.405 that leaves the pushrod length of 7.400 length pushrods. I hope I did this right.Did I do the math correct? If I used a 7.375 pushrod that made the preload
to about .050" and I thought that would not be enough.
10 1/2 turns on the pushrod checker = 0.525 6.800 + 0.525 = 7.325 now add preload of 0.080 = 7.405 that leaves the pushrod length of 7.400 length pushrods. I hope I did this right.Did I do the math correct? If I used a 7.375 pushrod that made the preload
to about .050" and I thought that would not be enough.
Last edited by transwiz; 05-22-2016 at 02:49 AM.
05-23-2016, 09:53 AM
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Your math looks good. I always recommend getting a 8" caliper and measuring directly vs counting rotations, but your numbers are realistic for a cam with the amount of lift you are using.
05-23-2016, 04:34 PM
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when i checked mine, i made sure my math/length was correct by checking to make sure my preload was correct too. i did this by using this information below to determine how many turns from zero lash equals the desired preload. since you want .08 preload you should be able to check this by setting your checker to 7.4 , setting it at zero lash and counting number of turns until you get to 22ft lbs. for .08 you should be at about one full turn or just a hair past it (assuming your bolt threads are 1.25mm pitch). at first i was just using the standard travel based on the pitch without accounting for the rocker ratio and my numbers never matched up. my numbers did not start to match up until i accounted for the ratio and then it all lined up perfectly and my measurements tied out to each other.
"You'll need to know the thread pitch first and then the preload per turn can be calculated. The common metric thread pitches are 1mm, 1.25mm, and 1.5mm but let's say it's a 1.25mm pitch. That means every turn of the bolt results in 1.25mm travel of the bolt or 1.25/25.4=.0492". Since the valve end of the rocker arm is essentially constrained from moving while turning the rocker arm bolt down from zero lash, it becomes the pivot point of the rocker and the movement at the pushrod end of the rocker arm gets multiplied by the ratio of the distance from the valve to the pushrod divided by the distance from the valve to the rocker arm bolt. Since it's just a ratio, the units and actual dimensions aren't really needed since we already know the ratio with the rocker arm bolt as the pivot point. We know the rocker arm ratio is 1.7:1 which means the distance from the pushrod to the rocker arm bolt is "1" and the distance from the rocker arm bolt to the valve is "1.7"...again, the units and actual dimensions aren't needed. That means the total rocker arm length from the valve to the pushrod is "2.7" so we have all the numbers we need...2.7/1.7=1.588. With a 1.25mm pitch, the lifter preload for each turn of the bolt will be .0492*1.588=.078" and each 1/4 turn will be .0195" or ~.020". For a 1mm pitch, one turn will be .0625" and 1/4 turn will be .0156". For a 1.5mm pitch, one turn will be .094" and 1/4 turn will be .0234"."
Read more: http://www.corvetteforum.com/forums/...#ixzz49W5XznLU
_Zblee
"You'll need to know the thread pitch first and then the preload per turn can be calculated. The common metric thread pitches are 1mm, 1.25mm, and 1.5mm but let's say it's a 1.25mm pitch. That means every turn of the bolt results in 1.25mm travel of the bolt or 1.25/25.4=.0492". Since the valve end of the rocker arm is essentially constrained from moving while turning the rocker arm bolt down from zero lash, it becomes the pivot point of the rocker and the movement at the pushrod end of the rocker arm gets multiplied by the ratio of the distance from the valve to the pushrod divided by the distance from the valve to the rocker arm bolt. Since it's just a ratio, the units and actual dimensions aren't really needed since we already know the ratio with the rocker arm bolt as the pivot point. We know the rocker arm ratio is 1.7:1 which means the distance from the pushrod to the rocker arm bolt is "1" and the distance from the rocker arm bolt to the valve is "1.7"...again, the units and actual dimensions aren't needed. That means the total rocker arm length from the valve to the pushrod is "2.7" so we have all the numbers we need...2.7/1.7=1.588. With a 1.25mm pitch, the lifter preload for each turn of the bolt will be .0492*1.588=.078" and each 1/4 turn will be .0195" or ~.020". For a 1mm pitch, one turn will be .0625" and 1/4 turn will be .0156". For a 1.5mm pitch, one turn will be .094" and 1/4 turn will be .0234"."
Read more: http://www.corvetteforum.com/forums/...#ixzz49W5XznLU
_Zblee
05-23-2016, 04:39 PM
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05-23-2016, 06:27 PM
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Sorry, I posted what I posted, but not the entire thought there.
