It’s all over the place on the CF and internet. Let’s see what the latest preferences are. More interested in what you have now, than “you know a guy who…”

 

Moved to C5 Tech.

 

.050" per turn
1 1/8 to 1 1/4 turn from zero lash = .056 to .063 If you are splitting hairs, .007 between all the cylinders.
I have 7.4 Push rods. GM performance LS7 Lifters PN 1249925.
Min would be .025 and max would be .150 according to Mr Holdener.


Scoggin-Dickey says .160 max on an LS7 lifter

 

Below is a snapshot from the SDPC tech guy who is measuring pushrods for pre load. Now this guy should know what the correct preload is, within a range. He works for a GM parts distributor and does tech videos on their behalf…

Here he states the GM spec is .030-.060, then says some people say .050-.100, so he aims for .050-.070. He doesn’t explain why he is not using the manufacturer (GM) spec.

Now, I’m not picking on this one guy, rather that this is typical of the videos, posts, and articles out there. It’s the preload dartboard.

What preload do you use?

 

I've always been an Olds guy before the Vette and are used to the non-adjustable valve-train with the pedestals rocker arms of those engines. If you had an SBC head guy sink a valve(s) into the heads without accounting for the recession by removing material off the stem would reek havoc with lifter pre-load. You'd have to whack the pedestal with a Bridgeport or shim with washers depending what you had. It was that or Crane adjustable rocker kit or adjustable push rods (never did that). PIA!!! The older SBC you could/would run with the valve covers off, back off till ticking and tighter 1/2 to one turn. Boom, Done. Old 80's feedback Electric Q-Jets noise due to dancing primary metering rods, would throw me for a loop on some old SBC and Olds engines thinking it was lifter noise.
Back to LS1 lifter preload topic....
Make sure you are not compressing the plunger in the lifter when looking for zero lash. I'm sure you have marinated your lifters so they are full of oil.
One of the reasons I decided on the LS7 lifter was the wide allowance of preload (.025 to .150/.160ish). I could have used 7.350 push rods for less preload but already had the 7.4 length and they are not seemingly loud. If I was zinging this thing to 7000+ rpm I would have gone with the 7.350 to get on the shorter side of the plunger pre-load stroke, but at that point I'd be into the $$$ Johnson lifters. Don't forget the original LS7 had a 7k rpm limit. My engine is planned to be running out of steam at about 6k rpm and these lifters are perfect for what I'm doing. Any noise I hear I attribute to the more aggressive lobes of the ramps on the TSP "Performance" cam. I'm sure my new lifters will never be as silent as the old lifters on the stock OEM lobes. 10k miles on the cam/lifters and still pulls like a freight train when pushed, with no change in perceived lifter noise at idle. One thing I wonder if there isn't some injector pulse noise I'm hearing with the hood open at idle... I close the hood and drive.
Didn't you whack the deck .020 on the heads to bump your Compression ratio? That missing .020 will effect your pre-load. Where are you at now, pre-load wise?

 

I had the heads milled 0.010”. My zero lash right now with new LS7 lifters is 7.300.

I have the stock 7.385 pushrods, 7.375 5/16” chromoly rods, and 7.400 11/32” chromoly rods to choose from.

Selecting from these rods, my preload could range from .075 to .100. According to the SDPC tech that is outside the GM specs, wink wink. Still, I know these lifters are commonly run outside that range. My head hurts.

 

7.350 should net you .050 of theoretical pre-load in the lifter if you are at 7.300 zero lash now. Unfortunately, looks like 7.350 is not in your quiver.
I edited my post above its ..050 per turn on the bolt.

 

I don't know where I got this, but saved it years ago from this forum. Last row is LS7 lifter, measurements are in mm. Full travel 0.166", and ideal preload 0.0823". I aimed for around 0.07" to 0.09" but I can't remember exactly the average worked out across all 8 cylinders.

 

 

What preload are YOU using ?

 

Did not vote, since I have not changed the cam yet, but my reading and experience has always been that preload has effects very similar to lash, i.e. less preload (more lash) results in more torque.
I have not tried it with rollers yet, but on Gen 1 small blocks 1/2 turn of preload would be measurably faster than 3/4 turn in the 1/4.

 

One YouTuber suggested checking all four corner lifters to look for machining on either a head or deck that was slanted fore/aft.

 

I haven't changed my lifters yet, but will plan to run Around .030-.050. But I also have adjustable rockers, so I can dial it in until it's silent.

 

Can't seem to find it now, but I recall reading here or another LS forum that someone checked multiple sets of pushrods just to see how consistent the lengths were -- it did not result in nearly as comforting a set of numbers as one might anticipate. We're discussing changes of 0.015" and rod to rod variation may be another 0.010" on top of that.

 

Not to mention that your heads may be different heights from the factory, or milled differently from front to back. Oh, and once the all aluminum engine is up to operating temp and expands, you lose about 0.010 to 0.015” preload.

 

Interesting post on turn method calculation…



https://www.corvetteforum.com/forums...post1578473349