98Redbird

Installing H/C and I read that the LS7 lifters have a different height than do the LS1 lifters. So the 7.4" pushrods that I have maybe will be too long and put too much preload on the lifters?? I think they said the difference in height was .050". 7.350" pushrods?

I do have a comp pushrod length checker 6.8"-7.8" but am unfamiliar with how to use it. Does anyone have a quick guide or how to on how to correctly measure this?

I would assume you just run the tool out to zero lash with the valvetrain tight and the cam on it's base circle. Take that value and then add desired preload?

What is desired preload on an ls7 lifter?

Z06supercharged

Pre-load on a LS7 lifter can be .040 - .130. Ive actually tried .040, .075 and .120 and all felt the same, idled the same and taken to 6800 the same. No big difference in noise either. GM specs show that .082 is the sweet spot cold and then as engine is hot that goes to about .075.

You are trying to get to the point where the lifter doesn't "tick tick" with the pushrod in place nor is the rocker snug. When you get the pushrod length such that you just barely get rid of the "tick tick", you have found "zero lash".
10. When you have found zero lash, carefully remove the rocker and pushrod without rotating the pushrod.
11. Tighten the pushrod until it is fully closed counting the turns as you go.

To figure out your pushrod length you do the following. Let’s assume it took 10-1/2 turns to close the pushrod down to its shortest length after you reached zero lash. Each turn is 0.050".

Your length is then: 6.800" (fully closed length) + 10.5 X 0.050" (number of turns times the length change per turn) = pushrod length minus preload. So for this case:

6.800 +10.5 X 0.050 = 7.325"

This is the length you measured to zero lash without any lifter preload. Now let’s say you want to have 0.075" lifter preload, you add that to the measured number and you end up with 7.400" pushrods.

99% of the time whatever PR length you have in there with LS1 lifters will still work just fine with LS7 lifters. When I swapped my ls6 lifters for ls7 lifters I kept my stock length PR's. I didnt need to go .050 shorter at all.

98Redbird

Z06 supercharged.... Thanks for taking the time to do that! I really appreciate it.

98Redbird

So when you say this, can you hear this "tick tick" by just rotating the motor over by hand? Without the lifters being "pumped up"

Z06supercharged

When you have the adj checker installed tighten it up to where you can barely turn it and then try to lift the rocker tip up and down. The "tick tick" is what you dont want to hear when you move the rocker tip up and down on the valve tip. The lifters dont need to be pumped up to do this. Do a search on comp cams adj pushrod checker, many hot to's will come up especially on ls1tech.

98Redbird

Thanks again man.

I was reading thru some other threads and apparently the LS7 lifter is the only one available now thru GM, so they are using it, it appears, as a drop in replacement without changing pushrod length. So I wouldnt' imagine I would need to change anything. Just as you said.

dougbfresh

I think your supposed to adjust length for optimal wipe on the top of the valve stem.

Z06supercharged

I believe that only works with aftermarket rockers that arent torqued down to 22 ft/lbs like our stock ones. I might be wrong on that but everything ive read about that using different length PR's wont do much for the wipe pattern with stock rockers as thjy cannot be dialed in as well as a set of adjustable post mounted roller rockers, in terms of valve wipe pattern. When I went from .040-.120 pre-load I saw very little if any wipe pattern difference so for me you get what you get wipe pattern wise with stock rockers.

Z06supercharged

With a head and cam change you must check for correct PR length, and even if existing heads are just milled . Do not just throw in PR's you had in. If just doing a lifter swap then existing PR's are usually fine.