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It's on a stock LS1, delphi ls7 lifters. I measured with 7.350 pushrods and a dial indicator. Do I need to go shorter? Or will I be ok?
The lifters are supposed to have 0.050-0.100in preload.
Ls7 lifters have something like .200" cup travel, so I would try it as is before spending any money. Pushrods are easy to change later if you get any valve float. Unless you have left out a detail such as a huge aftermarket cam, I doubt a little float would cause any PTV strike or otherwise do any harm.
Ls7 lifters have something like .200" cup travel, so I would try it as is before spending any money. Pushrods are easy to change later if you get any valve float. Unless you have left out a detail such as a huge aftermarket cam, I doubt a little float would cause any PTV strike or otherwise do any harm.
I agree it's not too hard to swap them out. Some people on other forums seem convinced that I will have valve float, and that scares me. I have the stock cam, and the trunnion upgrade on rockers, so it should all be the same.
It seems weird to me that the preload is this high, the lifters should only be 0.050" taller, so in theory 7.350" makes sense.
I agree it's not too hard to swap them out. Some people on other forums seem convinced that I will have valve float, and that scares me. I have the stock cam, and the trunnion upgrade on rockers, so it should all be the same.
It seems weird to me that the preload is this high, the lifters should only be 0.050" taller, so in theory 7.350" makes sense.
.110 preload on an LS7 lifter will not make it have valve float easier. Valve float is valve float. It's caused by over revving, it will happen whether you have .125 or .010 preload.
If you tighten the rockers down and get .110 preload that number never changes when the engine is running unless the rpm exceeds the limit of the valve springs and it gets valve train separation (valve float) which, like I said, is going to happen when you exceed the valve spring limits no matter what the preload is.
And FWIW dirt track racers used to use this as a cheat for years. They would put spacers in a hydraulic lifter so they would look stock and pass tech. They did this to reduce the amount of oil in the bottom of the lifter. More oil in the bottom of the lifter can get aerated and decrease lift.
So in short using longer pushrods gives you similar advantages of a short travel lifter. And that brings up another point .110 is almost in the middle of a an LS7 lifters travel. Short travel lifters recommended preload might be a lot less than .110 but it's still near the middle of their travel.
Lifter preload WILL change when the engine is running at operating temps, especially in an all aluminum engine. A .110" preload cold will reduce to probably .102"-.105". But you're correct. With standard LS7 roller lifters, .110" cold should be right in the middle of the .200" plunger travel of the lifter, and has nothing to do with valve float....
What issues are you having? Why does the internet think you have valve float?
In theory, with the only change being the upgrade to LS7 lifters, which are about 0.050" taller than the ls1 lifters, I should only need 7.350" pushrods. This is also according to numerous people here doing the same thing as me. So that's what I bought. When I put them in and measured my preload, I was only expecting to get around 0.050"-0.070" preload, at max 0.100". I didn't, after measuring multiple additional times, I measured around 0.110"-0.120" preload with 7.350" pushrods. Thats why everyone, particularly on reddit, seem adamant that id see valve float. I also got a proper pushrod measuring tool, with that, I also got 7.230" before preload, so 7.300" pushrods.
I've ended up buying some 7.300" pushrods, and I'll remeasure the preload when I get them, hopefully soon.
You guys are probably correct, I wouldn't see any valve float, but since I already have shorter rods on the way, I'll wait and test those before running it.
With te 7.350" pushrod, I tighten the bolt on the rocker arm until I cant feel any up down movement on the valve side. So zero lash. Then I place the tip of the dial indicator in the oil hole of the rocker arm, depressed a few tenths of an inch, zero it out, then tighten the rocker arm to 22ft lb and take that measurement.
Good video, thanks. I also found this in an article "We’ll save you the math conversion but the 8 x 1.25 thread pitch metric bolt is roughly equivalent to 20 threads per inch, so one full turn of adjustment would be equal to 0.050-inch of lifter preload and three-quarters-of-a-turn would be just under 0.040-inch"
The rocker arm is a lever https://en.wikipedia.org/wiki/Lever. The bolt moves the center point of the 3 that are involved with its lever function. Since the rocker ratio in these motors is 1.7:1, then the distance that the push rod end of the rocker moves is MULTIPLIED BY the total end-to-end length of the lever (rocker arm length... the distance from the valve stem to the bolt, which is 1.7 units, PLUS the distance from the bolt to the push rod, which is 1.0 of the same units) divided by the part from the "fulcrum" (the valve stem end, in this usage) to the bolt (again, 1.7 units). This is (1.7 + 1) ÷ 1.7. Which means then, that 1 turn on the bolt (which is indeed plenty close enough to .040" for the task at hand), is about .063" at the push rod end. 1¼ turn would be about .079".
The rocker arm is a lever https://en.wikipedia.org/wiki/Lever. The bolt moves the center point of the 3 that are involved with its lever function. Since the rocker ratio in these motors is 1.7:1, then the distance that the push rod end of the rocker moves is MULTIPLIED BY the total end-to-end length of the lever (rocker arm length... the distance from the valve stem to the bolt, which is 1.7 units, PLUS the distance from the bolt to the push rod, which is 1.0 of the same units) divided by the part from the "fulcrum" (the valve stem end, in this usage) to the bolt (again, 1.7 units). This is (1.7 + 1) ÷ 1.7. Which means then, that 1 turn on the bolt (which is indeed plenty close enough to .040" for the task at hand), is about .063" at the push rod end. 1¼ turn would be about .079".
I was just thinking about this, you're correct.
If the bolt goes down 0.0492126in (1in/20.32tpi) every turn, thats 0.078161in preload on the lifter.
Last edited by Preston.Corvette; Feb 13, 2024 at 01:55 PM.
I just did some calculation and come up with something slightly different.
If the thread pitch is 1.25mm the decimal equivalent equals to .0492" for one full turn.
Then 11/4 turns would be 1.25 x .0492" = .0615" rounded off to .062"
Correct me if I'm wrong.
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Is 0.1035 too much preload? 
