Preload.. 1 turn = .047" is this really accurate?
06-18-2010, 11:42 AM
#1
Preload.. 1 turn = .047" is this really accurate? Ok, so yesterday I decided to doudle check a few things in my valve train. I'm about to switch to a new cam, but figured, I'd double check things any way.
Cyl I am checking is in it's power stroke, both valves are closed.
Pulling a rocker arm and using an adjustable push rod checker, here is what I did.
Put the push rod in at x.xx" height
Tightened the stud by hand using a socket till there was 0 lash. This seemed to be about the same point in which I could no longer turn the stud. However, I could see the push rod push down slightly in the hole. If I went to where it stoped with out the push rod compressing a little, then I could still push down on the back of the rocker and get the tip to come off the valve making it click.
Mark rocker stud position
Tighten down to 22lbs while counting turns
Here are my findings:
Intake:
7.35" = 1/4 turn
7.40" = 5/8 turn
7.45" = 1 1/8 turn
7.50" = 1 1/2 turn
Exhaust:
7.35" = 1/4 turn
7.40" = 5/8 turn
7.45" = 1 5/8 turn
7.50" = 2 turns
The 2 things I have that I guess could throw my data off are:
I chose the #8 cyl to check because it was in the power stroke to begin with, sitting on the base circle of the cam.
I drove the truck aprox 24 hours prior to checking it.
Would the above cause the lifter to show different readings do to oil in them? IE not bled down?
Any in put would be great. BTW, lifters are CTS-V..
Cyl I am checking is in it's power stroke, both valves are closed.
Pulling a rocker arm and using an adjustable push rod checker, here is what I did.
Put the push rod in at x.xx" height
Tightened the stud by hand using a socket till there was 0 lash. This seemed to be about the same point in which I could no longer turn the stud. However, I could see the push rod push down slightly in the hole. If I went to where it stoped with out the push rod compressing a little, then I could still push down on the back of the rocker and get the tip to come off the valve making it click.
Mark rocker stud position
Tighten down to 22lbs while counting turns
Here are my findings:
Intake:
7.35" = 1/4 turn
7.40" = 5/8 turn
7.45" = 1 1/8 turn
7.50" = 1 1/2 turn
Exhaust:
7.35" = 1/4 turn
7.40" = 5/8 turn
7.45" = 1 5/8 turn
7.50" = 2 turns
The 2 things I have that I guess could throw my data off are:
I chose the #8 cyl to check because it was in the power stroke to begin with, sitting on the base circle of the cam.
I drove the truck aprox 24 hours prior to checking it.
Would the above cause the lifter to show different readings do to oil in them? IE not bled down?
Any in put would be great. BTW, lifters are CTS-V..
06-18-2010, 12:04 PM
#2
Here's what I did. I had measured my preload with a dial indicator. I knew I had 0.050" preload. I then used the turn counting method. I found that it tool 5/8 turn for the rocker to bottom against the head and the 1/3 turn to reach torque (tighten the bolt). Using the 5/8 turn I get:
5/8 X 1.25/25.4 X 2.7/1.7 = 0.049"
The thing to remember, the 1/3 turn to tight the bolt remains constant, in other words as you scale you build in more error but it isn't a lot.
5/8 X 1.25/25.4 X 2.7/1.7 = 0.049"
The thing to remember, the 1/3 turn to tight the bolt remains constant, in other words as you scale you build in more error but it isn't a lot.
06-18-2010, 02:31 PM
#3
I had a similar experience with zero lash at the valve stem, vs zero lash at the push rod... Zero lash at the valve stem seemed to provide a measurable amount of lifter pre-load. I snugged the rocker bolts down until I had zero movement in the push rod, then torqued to 25 ft/lbs. I got about 1 1/4+ turns on each to get to 25 ft/lbs.
If I zero lashed based on the valve stem, It would only take 3/4 turn to achieve the same torque on the bolts. Granted, I was checking when the heads weren't torqued down, but even after I did torque them down, there was a slight difference.
If I zero lashed based on the valve stem, It would only take 3/4 turn to achieve the same torque on the bolts. Granted, I was checking when the heads weren't torqued down, but even after I did torque them down, there was a slight difference.
06-18-2010, 04:30 PM
#7
I am using Comp Cams adjustable push rod. Part number 7702-1 which has a static height of 6.8. Every rotation = .050". To achieve 7.35 I turned it out 11 times. 7.40 turned it 12 times ect..
For each height Iset it going in, when pulling it out, I verified it was still where I set it.
Trending Topics
06-18-2010, 04:49 PM
#8
FormerVendor
iTrader: (2)
Join Date: Dec 2001
Location: Baton Rouge, LA, USA
Posts: 1,954
Likes: 0
Received 3 Likes
on
3 Posts
A couple of points...
Lifter bleed down has absoloutly no effect on preload. The lifter plunger is help "up" by an internal spring when the lifter is not loaded.
Checking lifter preload on the "power" or compression stroke is not an accurate way to check. A better method is using the EO/IC method. Since you got two different results for the same cylinder this shows one of the lifters was not completely on the base circle.
I have actually measured lifter preload directly by using a dial indicator on the pushrod end of the rocker. For a LSx engine with 1.7 rockers and an 8mm X 1.25 rocker bolt, the .047" preload number is accurate. I've also done back to back dyno testing with various preload values and seen little if any differences between any reasonable value.
I guess the bottom line is, with any "stock type" lifter I shoot for 1 to 1 1/2 turns from zero lash. I have found this value to give the best overall valvetrain longevity and power with the least amount of noise.
I hope this helps.
Shane
Lifter bleed down has absoloutly no effect on preload. The lifter plunger is help "up" by an internal spring when the lifter is not loaded.
Checking lifter preload on the "power" or compression stroke is not an accurate way to check. A better method is using the EO/IC method. Since you got two different results for the same cylinder this shows one of the lifters was not completely on the base circle.
I have actually measured lifter preload directly by using a dial indicator on the pushrod end of the rocker. For a LSx engine with 1.7 rockers and an 8mm X 1.25 rocker bolt, the .047" preload number is accurate. I've also done back to back dyno testing with various preload values and seen little if any differences between any reasonable value.
I guess the bottom line is, with any "stock type" lifter I shoot for 1 to 1 1/2 turns from zero lash. I have found this value to give the best overall valvetrain longevity and power with the least amount of noise.
I hope this helps.
Shane
06-18-2010, 04:57 PM
#9
I am using Comp Cams adjustable push rod. Part number 7702-1 which has a static height of 6.8. Every rotation = .050". To achieve 7.35 I turned it out 11 times. 7.40 turned it 12 times ect..
For each height Iset it going in, when pulling it out, I verified it was still where I set it.
For each height Iset it going in, when pulling it out, I verified it was still where I set it.
06-18-2010, 05:04 PM
#10
Both lifters for #8 were on the base circle of the cam. I rotated it over this morning to put #2 TDC so I could check a few more things out on the Valver train. I watch the rockers for movement. I wanted to pull a couple springs and check install height for the new cam (Number 2 is the easiest to get to) and also check spring pressure since the springs have been on for a while now.
Look at the begining numbers. both 7.35 and 7.40 required the same amount of turns to reach 22lbs. The difference was once the push rod got longer 7.45 and 7.50 that the numbers went away from each other. That is something I find very puzzling.
Now, I don't know it all, and that's why I'm asking questions.. So I have another one for you.. In what way is EO/IC going to be more accurate than with the lifter on the base circle? I find that almost contrary to what you are telling me.
If your checking both intake and exhaust while EO/IC your exhaust is obviously not on the base circle of the cam. See my point? Are you telling me to check I while EO and to check E while IO?
06-18-2010, 06:16 PM
#11
TECH Senior Member
iTrader: (96)
Join Date: Aug 2007
Location: Turnin' Wrenches Infractions: 005
Posts: 24,240
Likes: 0
Received 81 Likes
on
72 Posts
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
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
06-18-2010, 07:05 PM
#12
Yes. If the intake is open the exhaust is closed and vice versa. The other thing to be careful of is if you have the regular springs in there and are using an adjustable, the threads of the adjustable have some tolerance in them that will be taken up by the spring force as they are not solid like a regular pushrod and this can skew your results some.
06-18-2010, 07:16 PM
#13
I figured there might be a little slack in the adjustable push rod. But The 2 I have are brand new and feel pretty solid. So hopefully that's not an issue.
Well, I started pulling the passanger side completely apart as far as valve train goes. I have the springs off as well as the seals and hardened spring locators. Measured my spring heights straight to the head surface (Using a Comp cams spring height checker) to figure out what I'm going to need to run to get a 1.80" install height. Not sure what I'm going to do now. The intakes are going to be hard to get there as I believe I can't let the spring ride on the aulum surface of the head.
2e = 1.83
2i = 1.81
4e = 1.839
4i = 1.81
6e = 1.835
6i = 1.81
8e = 1.835
8i = 1.81
Well, I started pulling the passanger side completely apart as far as valve train goes. I have the springs off as well as the seals and hardened spring locators. Measured my spring heights straight to the head surface (Using a Comp cams spring height checker) to figure out what I'm going to need to run to get a 1.80" install height. Not sure what I'm going to do now. The intakes are going to be hard to get there as I believe I can't let the spring ride on the aulum surface of the head.
2e = 1.83
2i = 1.81
4e = 1.839
4i = 1.81
6e = 1.835
6i = 1.81
8e = 1.835
8i = 1.81
06-18-2010, 07:56 PM
#15
I figured there might be a little slack in the adjustable push rod. But The 2 I have are brand new and feel pretty solid. So hopefully that's not an issue.
Well, I started pulling the passanger side completely apart as far as valve train goes. I have the springs off as well as the seals and hardened spring locators. Measured my spring heights straight to the head surface (Using a Comp cams spring height checker) to figure out what I'm going to need to run to get a 1.80" install height. Not sure what I'm going to do now. The intakes are going to be hard to get there as I believe I can't let the spring ride on the aulum surface of the head.
2e = 1.83
2i = 1.81
4e = 1.839
4i = 1.81
6e = 1.835
6i = 1.81
8e = 1.835
8i = 1.81
Well, I started pulling the passanger side completely apart as far as valve train goes. I have the springs off as well as the seals and hardened spring locators. Measured my spring heights straight to the head surface (Using a Comp cams spring height checker) to figure out what I'm going to need to run to get a 1.80" install height. Not sure what I'm going to do now. The intakes are going to be hard to get there as I believe I can't let the spring ride on the aulum surface of the head.
2e = 1.83
2i = 1.81
4e = 1.839
4i = 1.81
6e = 1.835
6i = 1.81
8e = 1.835
8i = 1.81
06-18-2010, 09:29 PM
#16
Not sure where you are getting the 1.800" install height from but all the stock heads I have done set up at around 1.765" unshimmed with seat in place. You can't run them on the aluminum, you must have either a seat or the one piece seat/seal if running beehive springs.
I'm getting recomended instal height of 1.80" from the spring manufacture (Crane http://cranecams.com/?show=browsePar...mber=144832-16) I would assume they are talking about having the locator in place, but perhaps they are talking total free height with out it.
The new cam I am putting in has .644/.625 lift. Crane says at 1.80" install height they can go to .650 lift with .060" clearnce (1.80 - .650 = 1.15.. Coil bind is at 1.045)
The Valve spring locator from Crane is .050 thick (http://cranecams.com/?show=browsePar...mber=144460-16)
1.81 - .050 (locator) = 1.76 install height
1.76 - .644 (Cam Lift) = 1.116 compressed spring height at full lift
1.116 - 1.045 (coil bind) = .0.071 clearence
I supose that should work since Crane calls for .060" clearnece.
Last edited by LIL SS; 06-18-2010 at 09:41 PM.
06-19-2010, 07:55 AM
#18
Especially with duals, one of the two spings can coilbind before the other, so you have to check CB on both and install from the higher CB height, or match inners an outters based on CB height.
06-19-2010, 02:40 PM
#19
FormerVendor
iTrader: (2)
Join Date: Dec 2001
Location: Baton Rouge, LA, USA
Posts: 1,954
Likes: 0
Received 3 Likes
on
3 Posts
I figured there might be a little slack in the adjustable push rod. But The 2 I have are brand new and feel pretty solid. So hopefully that's not an issue.
Well, I started pulling the passanger side completely apart as far as valve train goes. I have the springs off as well as the seals and hardened spring locators. Measured my spring heights straight to the head surface (Using a Comp cams spring height checker) to figure out what I'm going to need to run to get a 1.80" install height. Not sure what I'm going to do now. The intakes are going to be hard to get there as I believe I can't let the spring ride on the aulum surface of the head.
2e = 1.83
2i = 1.81
4e = 1.839
4i = 1.81
6e = 1.835
6i = 1.81
8e = 1.835
8i = 1.81
Well, I started pulling the passanger side completely apart as far as valve train goes. I have the springs off as well as the seals and hardened spring locators. Measured my spring heights straight to the head surface (Using a Comp cams spring height checker) to figure out what I'm going to need to run to get a 1.80" install height. Not sure what I'm going to do now. The intakes are going to be hard to get there as I believe I can't let the spring ride on the aulum surface of the head.
2e = 1.83
2i = 1.81
4e = 1.839
4i = 1.81
6e = 1.835
6i = 1.81
8e = 1.835
8i = 1.81
You will need to take into account the fact that most retainers for a stock diameter spring will fall into the top of the height mic to some degree. With the proper locator and retainer on a stock head you should come out very close to 1.800" installed height. Also, just an FYI, those 144832's won't be long for this world with a cam that aggressive. I always thought Crane was out of their minds with the rating on that spring. Get a good set of Comp or Manley springs and sleep better at night. I sold those 832's for years when there wasn't any other choice but there are much better choices now especially with a cam that aggressive. Crane's lobe designs were always very lazy which allowed them to run those springs. You won't get away with that cam and those springs for long...
Shane
06-19-2010, 02:53 PM
#20
TECH Junkie
iTrader: (2)
Join Date: Jan 2006
Location: Fort Wayne, IN
Posts: 3,776
Likes: 0
Received 0 Likes
on
0 Posts
I'm getting recomended instal height of 1.80" from the spring manufacture (Crane http://cranecams.com/?show=browsePar...mber=144832-16) I would assume they are talking about having the locator in place, but perhaps they are talking total free height with out it.
The new cam I am putting in has .644/.625 lift. Crane says at 1.80" install height they can go to .650 lift with .060" clearnce (1.80 - .650 = 1.15.. Coil bind is at 1.045)
The Valve spring locator from Crane is .050 thick (http://cranecams.com/?show=browsePar...mber=144460-16)
1.81 - .050 (locator) = 1.76 install height
1.76 - .644 (Cam Lift) = 1.116 compressed spring height at full lift
1.116 - 1.045 (coil bind) = .0.071 clearence
I supose that should work since Crane calls for .060" clearnece.
The new cam I am putting in has .644/.625 lift. Crane says at 1.80" install height they can go to .650 lift with .060" clearnce (1.80 - .650 = 1.15.. Coil bind is at 1.045)
The Valve spring locator from Crane is .050 thick (http://cranecams.com/?show=browsePar...mber=144460-16)
1.81 - .050 (locator) = 1.76 install height
1.76 - .644 (Cam Lift) = 1.116 compressed spring height at full lift
1.116 - 1.045 (coil bind) = .0.071 clearence
I supose that should work since Crane calls for .060" clearnece.