Pushrod, lifter preload (math check)
11-08-2011, 08:38 PM
#1
Pushrod, lifter preload (math check) measured today for the correct length push rods for my new cam and new LS7 lifters and trays...
1st) some simple math before measuring, ok old stock cam base circle was 1.55", new cams base circle is smaller 1.45". Difference of 0.1" from old cam to new cams base circle... stock pushrods are 7.4" with stock preload being around .065" or so ( i think). theoretical i should be using 0.10" longer pushrods to get the same preload = new cam would require 7.5" pushrods.
i did port the heads but just cleaned up the decks with Wd-40 and scotch bright pad, there wasn't any reason to clean them up at a machine shop. I also put on new Head gaskets (felpro 26190PT, i called felpro and they told me the compressed thickness of this gasket is the same as the stock gasket compressed thickness, i think it is .50"), i am also using new LS7 lifters.
2) i used my comp cams adjustable pushrod checker to check for correct length and preload.... basically i get with 7.5" push rods 0.0705" of lifter preload. I accomplished this by using the 0 lash then torque to 22ft/lbs method. i extended my pushrod checker 14 turns (starting length is 6.80" + 14 turns (@.050" pr/turn) = 7.5". then i put it in snugged up the rocker to 0 lash, then went to 22 ft/lbs which took 1 and 1/2 turns to reach 22ft/lbs..
sound correct?
also i did this five times to make sure of my measurements and got a little different measurements each time, due to my lack of getting a perfect 0 lash (and it was getting dark on me). the lowest of my five numbers was .0646" and the highest was .07343". If i average all five numbers together I get .06815" lifter preload
sound about right?
1st) some simple math before measuring, ok old stock cam base circle was 1.55", new cams base circle is smaller 1.45". Difference of 0.1" from old cam to new cams base circle... stock pushrods are 7.4" with stock preload being around .065" or so ( i think). theoretical i should be using 0.10" longer pushrods to get the same preload = new cam would require 7.5" pushrods.
i did port the heads but just cleaned up the decks with Wd-40 and scotch bright pad, there wasn't any reason to clean them up at a machine shop. I also put on new Head gaskets (felpro 26190PT, i called felpro and they told me the compressed thickness of this gasket is the same as the stock gasket compressed thickness, i think it is .50"), i am also using new LS7 lifters.
2) i used my comp cams adjustable pushrod checker to check for correct length and preload.... basically i get with 7.5" push rods 0.0705" of lifter preload. I accomplished this by using the 0 lash then torque to 22ft/lbs method. i extended my pushrod checker 14 turns (starting length is 6.80" + 14 turns (@.050" pr/turn) = 7.5". then i put it in snugged up the rocker to 0 lash, then went to 22 ft/lbs which took 1 and 1/2 turns to reach 22ft/lbs..
sound correct?
also i did this five times to make sure of my measurements and got a little different measurements each time, due to my lack of getting a perfect 0 lash (and it was getting dark on me). the lowest of my five numbers was .0646" and the highest was .07343". If i average all five numbers together I get .06815" lifter preload
sound about right?
11-09-2011, 04:11 AM
#2
1st) some simple math before measuring, ok old stock cam base circle was 1.55", new cams base circle is smaller 1.45". Difference of 0.1" from old cam to new cams base circle... stock pushrods are 7.4" with stock preload being around .065" or so ( i think). theoretical i should be using 0.10" longer pushrods to get the same preload = new cam would require 7.5" pushrods.
Stock pushrods are not exactly 7.400" length according to another user who allegedly took precision measurements.
Hope you used something like brake parts cleaner or denatured alcohol after the WD-40.
11-09-2011, 04:47 AM
#3
See below. Hope this helps.
measured today for the correct length push rods for my new cam and new LS7 lifters and trays...
1st) some simple math before measuring, ok old stock cam base circle was 1.55", new cams base circle is smaller 1.45". Difference of 0.1" from old cam to new cams base circle... stock pushrods are 7.4" with stock preload being around .065" or so ( i think). theoretical i should be using 0.10" longer pushrods to get the same preload = new cam would require 7.5" pushrods.
As stated above, it appears you are using diameter whereas the actual lifter displacement due to the base circle change should use radius of the base circle. Also, I have measured several sets of stock pushrods and the actual length is 7.385" gauge lengths. 7.400" has been established as stock on the internet but is not correct. I think it is because this is a standard length that is used by vendors for cam swaps. As you can see, the 7.385" to 7.400" difference is 0.015" of gauge length and with a 0.025" radius change of base circle you are within 0.010" of the original stock preload. Note that none of these numbers are absolutely exact but are nominal values.
i did port the heads but just cleaned up the decks with Wd-40 and scotch bright pad, there wasn't any reason to clean them up at a machine shop. I also put on new Head gaskets (felpro 26190PT, i called felpro and they told me the compressed thickness of this gasket is the same as the stock gasket compressed thickness, i think it is .50"), i am also using new LS7 lifters.
2) i used my comp cams adjustable pushrod checker to check for correct length and preload.... basically i get with 7.5" push rods 0.0705" of lifter preload. I accomplished this by using the 0 lash then torque to 22ft/lbs method. i extended my pushrod checker 14 turns (starting length is 6.80" + 14 turns (@.050" pr/turn) = 7.5". then i put it in snugged up the rocker to 0 lash, then went to 22 ft/lbs which took 1 and 1/2 turns to reach 22ft/lbs..
sound correct?
Not sure how you are getting the preload here. You should open the adjustable to obtain zero lash with the rocker snugged in place and take the measurement. Then add preload.
Don't rely on counting tocker bolt turns, which is what I think you are doing. If you have a dial indicator you can measure directly otherwise use the zero lash method and adding. Using 1-1/2 turns to 22 lb-ft I get a preload of 0.091" using math.
also i did this five times to make sure of my measurements and got a little different measurements each time, due to my lack of getting a perfect 0 lash (and it was getting dark on me). the lowest of my five numbers was .0646" and the highest was .07343". If i average all five numbers together I get .06815" lifter preload
This is normal as there will be differences between each valve, etc. due to tolerances, measurement errors, etc. It is good to verify and make sure there aren't any out of whack though.sound about right?
1st) some simple math before measuring, ok old stock cam base circle was 1.55", new cams base circle is smaller 1.45". Difference of 0.1" from old cam to new cams base circle... stock pushrods are 7.4" with stock preload being around .065" or so ( i think). theoretical i should be using 0.10" longer pushrods to get the same preload = new cam would require 7.5" pushrods.
As stated above, it appears you are using diameter whereas the actual lifter displacement due to the base circle change should use radius of the base circle. Also, I have measured several sets of stock pushrods and the actual length is 7.385" gauge lengths. 7.400" has been established as stock on the internet but is not correct. I think it is because this is a standard length that is used by vendors for cam swaps. As you can see, the 7.385" to 7.400" difference is 0.015" of gauge length and with a 0.025" radius change of base circle you are within 0.010" of the original stock preload. Note that none of these numbers are absolutely exact but are nominal values.
i did port the heads but just cleaned up the decks with Wd-40 and scotch bright pad, there wasn't any reason to clean them up at a machine shop. I also put on new Head gaskets (felpro 26190PT, i called felpro and they told me the compressed thickness of this gasket is the same as the stock gasket compressed thickness, i think it is .50"), i am also using new LS7 lifters.
2) i used my comp cams adjustable pushrod checker to check for correct length and preload.... basically i get with 7.5" push rods 0.0705" of lifter preload. I accomplished this by using the 0 lash then torque to 22ft/lbs method. i extended my pushrod checker 14 turns (starting length is 6.80" + 14 turns (@.050" pr/turn) = 7.5". then i put it in snugged up the rocker to 0 lash, then went to 22 ft/lbs which took 1 and 1/2 turns to reach 22ft/lbs..
sound correct?
Not sure how you are getting the preload here. You should open the adjustable to obtain zero lash with the rocker snugged in place and take the measurement. Then add preload.
Don't rely on counting tocker bolt turns, which is what I think you are doing. If you have a dial indicator you can measure directly otherwise use the zero lash method and adding. Using 1-1/2 turns to 22 lb-ft I get a preload of 0.091" using math.
also i did this five times to make sure of my measurements and got a little different measurements each time, due to my lack of getting a perfect 0 lash (and it was getting dark on me). the lowest of my five numbers was .0646" and the highest was .07343". If i average all five numbers together I get .06815" lifter preload
This is normal as there will be differences between each valve, etc. due to tolerances, measurement errors, etc. It is good to verify and make sure there aren't any out of whack though.sound about right?
11-09-2011, 10:37 AM
#4
Vettenuts thank you for your reply... i have well how do you say it... extra large mitts and there is no way my fingers can turn the pushrod while it is installed into place. thanks for your tip about radius and diameter. I missed that one when doing my math last night... can you describe to me your method for using a dial indicator to find 0 lash.
Last edited by 3rdCoastPowerSports; 11-09-2011 at 01:57 PM.
11-09-2011, 12:00 PM
#5
Also, I have measured several sets of stock pushrods and the actual length is 7.385" gauge lengths. 7.400" has been established as stock on the internet but is not correct. I think it is because this is a standard length that is used by vendors for cam swaps.
I do know however, that Manton pushrod length is defined from flat-to-flat (details on this are in their catalog).
If the OP used a Comp Cams adjustable pushrod, then he has measured the "gauge length" that he requires, as the tool is calibrated to their "gauge length" measurement system.
11-09-2011, 12:10 PM
#6
2) i used my comp cams adjustable pushrod checker to check for correct length and preload.... basically i get with 7.5" push rods 0.0705" of lifter preload. I accomplished this by using the 0 lash then torque to 22ft/lbs method. i extended my pushrod checker 14 turns (starting length is 6.80" + 14 turns (@.050" pr/turn) = 7.5". then i put it in snugged up the rocker to 0 lash, then went to 22 ft/lbs which took 1 and 1/2 turns to reach 22ft/lbs..
sound correct?
sound correct?
also i did this five times to make sure of my measurements and got a little different measurements each time, due to my lack of getting a perfect 0 lash (and it was getting dark on me). the lowest of my five numbers was .0646" and the highest was .07343". If i average all five numbers together I get .06815" lifter preload
sound about right?
sound about right?
11-09-2011, 01:41 PM
#7
i read an interesting article in September issue of Car Craft on hydraulic lifters they recommend limiting the preload to around 0.010-0.015, the idea is to limit the amount of preload so when the valvetrain experiences separation the reduced amount of preload is not enough to hold the valve open. woundering what your thoughts are on this because i am thinking of changing the p-rod length to adjust my preload as they described.
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11-09-2011, 01:51 PM
#8
i read an interesting article in September issue of Car Craft on hydraulic lifters they recommend limiting the preload to around 0.010-0.015, the idea is to limit the amount of preload so when the valvetrain experiences separation the reduced amount of preload is not enough to hold the valve open. woundering what your thoughts are on this because i am thinking of changing the p-rod length to adjust my preload as they described.
11-09-2011, 02:04 PM
#9
first i have heard of it as well. i think the premise of the article was to be able to get solid lifter performance out of hydraulic lifters, they also recommended some serious springs to go with it something like 200 lbs of pressure closed and 450 open. think doin this may cause more problems than its worth prolly should shoot for middle of the road too.
11-09-2011, 06:40 PM
#10
just so you know you come off as an ******* in every single post i have read by you and every single post of mine that you have replied too, maybe your not but you should work on the way you words things,, and dont remind me about how new to the website i am and how long you have been on,,, i do respect your knowledge you just present it in a dick sort of way.
