Wanted some options on this before I bought new pushrods. I bought the comp cam length checker and followed the instructions as many have posted on this site! I just wanted some options to see if this seems right or not!

Here is my combo.
6.0 bored 30 over
DSS Flat tops -5cc
Scat I beam (6.125)
Stock crank
243 casting heads milled .030
BTR springs .660 lift
LS3 head gaskets (5 layer) .051
Stock rockers with trunion upgrade
Cam spec 239/247 .642/.632 108+4
LS7 lifters

So according to the directions I ran it out to 0 lash.. which was 10.5 turns. So 6.800 + (10.5 X .50 = 5.25) = 7.325
Then add in the preload value which I figure would be about .050.
Which gives me 7.375.
Could anyone tell me if that sounds about right?

Thanks in advance!!

 

7.4 I run

 

Sounds correct...
Measured amount plus desired preload = Total pushrod length..

Personally I shoot for .020 - .025 preload Which would put you at 7.350

 

Is there a reason why you shoot for .020 - .025 preload?

 

In General, less lifter preload is used to prevent "Lifter pump up" at higher rpm's...

effectively, limiting the amount the lifter can pump up under higher oil pressures and flow volumes...

the more preload you use, the farther it can "pump up"

when the lifter pumps up it effectively acts like valve float and hangs the valve open....
this can cause piston to valve contact, as well as cause just a loss in power in general at higher rpm's


all cam manufacturers recommend going with .020~.060 preload in general due to the more aggressive ramp rates of an aftermarket cam lobe.

 

http://www.hotrod.com/how-to/engine/...ngth-pushrods/
In this article they talk about wipe pattern. They use a 1st gen small block as their example but it still pertains. They suggest using checking springs when turning the crank to not damage the tool but do not mention using a solid lifter. For our engines, I've read of people taking apart a LS1 roller lifter and filling it with washers to make a "solid" lifter because sometimes the strength of the checking springs is enough to collapse the spring in the oil-empty lifter.
First, let me say, I have no experience. I've been gathering notes for my first cam and head install. I'm poking my nose in your thread because I am interested in what soundengineer said about preload.
7.375" does sound right because stock is 7.4 and your milled 0.030
So what I take from the article as it applies to the LSx is to use preload to get the correct wipe pattern on your valve tips, since pushrods are usually sold in .025" increments.
Many builders say the minimum piston to valve clearance you should run is 0.070" on the intake. If this is what you have and you run 0.080 preload, if you pump-up your going to contact. If you run 0.041" and you pump up you would barely contact just because of heat expansion. You have to multiply your preload by your rocker ratio (1.7) to know the full extent of what pump-up will do to your PtV.

I assumed to run such a small preload you had to have short travel lifters.

I copied this from another post, some Cajun:
Pushrod length without a pushrod tool
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 with 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...
Kacuziken, that should be a VERY potent engine.

 

the part in RED is wrong

one full turn is .078 Preload
since you are pushing down on the center of the rocker, based on a 1.7 rocker ratio, it will only move the center .049..... the end of the rocker will mover further by the 1.7 ratio since the tip does not move because it should be resting on the top of a closed valve

if you need a visual aid....lay a pencil , hold the pencil point with your finger......then grasp it somewhere in the middle and move that spot down without moving the tip that you are holding with your other hand...
the eraser end will move further than the middle part you are moving.

you can also find this out by actually physically measuring the distance the rocker cup moves (which I have done many times to check actual preload)





the Part in MAGENTA is a very poor practice and you are asking for problems with lifters with too much preload
the ls7 lifters are only designed for a MAXIMUM travel of .130 when bottomed out
LS1 lifters had a maximum travel of .160

if you have an LS7 lifter, 1.75 turns would be .1365...which means you have bottomed out the lifter and are starting to open the valve


you should always shoot for 1/4~1/2 turn after zero lash...1 full turn at the Most...

 

also... if you collapse a lifter with a checker spring, either your lifter is BAD or you are not using the right checker spring.

it is a bit more tricky to measure with a hydraulic lifter than it is with a solid lifter,but it can be done just the same.


you can also Ignore that article about how to adjust wipe pattern as most of it does not apply to a hydraulic lifter with a Rocker arm that rests on a pedestal

it only applies to a floating rocker like a conventional small block/ big block uses.

once you have a rocker that rests on a pedestal like the LS1 does, the only way to adjust wipe pattern is to shim or shave the rocker pedestal, or change the install height of the valve by using a shorter or longer valve


if you have an aftermarket camshaft with more lift (and nothing changes with the gasket/heads/valves), you will have to shim the rocker pedestal by 1/2 of the extra lift to get back to stock geometry to keep the wipe pattern the same as stock
the smaller base circle and the different pushrod length doesnt affect this with a hydraulic lifter
if you use a solid lifter then you would take into account the smaller base circle of most aftermarket cams for your rocker geometry.

the rocker should move outward and then back inwards over the tip if the geometry is correct

 

I appreciate the heads up. I will edit my notes to remove that practice and add what you said about physically measuring the distance the rocker cup moves . Thank you for that correction.
Which would change pushrod length ?
Kacuziken's cam has alot of lift, I wonder how his wipe pattern will turn out.

 

If you shim the pedestal to get geometry correct, it would make pushrod length longer if you did not want to change preload amount..

part of the reason aftermarket cams use the smaller base circle is to fix the change in geometry some

if you go to a .650 lift cam the geometry gets out of whack by .075 to .080
(stock lift ls1 cam is .496 lift IIRC)
the smaller base circle is only about .025 smaller(at the most)...so you have another .050+ to make up to keep geometry the same as stock

most people dont realize this,and most just dont worry about it...
its not enough to cause major issues typically...
but over .630 lift you start to wear out the valve tips and valve guides because the rocker is way up on its nose and pushing at an angle on the valve.....so its best at that point to switch to a pedestal mount roller rocker...ones that come with their own stand are typically a little tiny bit higher than stock, so it fixes the geometry some for you.

 

While I don't disagree with the math used to obtain your value of 0.078", I did a check on my own of this method that is taken at face value on this forum. What I found was that of the 1 turn required to obtain 22 lb-ft, 1/3 turn was used to tighten the bolt from when the rocker bottoms to the torque of 22 lb-ft. That effectively gives 2/3 turn of actual preload, or 0.052" or approximately the internet value of 0.047" preload. The issue becomes that once you go over 1 turn, many simply multiply the turns by 0.047". For example, 2 turns is stated to be 0.094". However, you still need to correct for the 1/3 turn such that with 2 turns to 22 lb-ft, only 1-2/3 turns are actually preloading the lifter. The relationship is non-linear.

 

this is why measuring overall lengths instead of counting turns is awesome. you remove all guesswork