White40thGT

iTrader: (1)

I have been concerned about my preload, and found a post that detailed an easy way to check without a dial indicator.

https://ls1tech.com/forums/11820615-post5.html


So I did all of this as the instructions stated and I got roughly 1.25 turns which should put me dead on the money.

However, what I do not know is if the car should be hot or cold when doing this, and if it matters. I would assume that it would matter due to lifters bleeding down. At the time of the test I had driven the car for about 15 minutes, and let it sit for about 20 minutes with a shop fan pointed at the car.

Should lifter preload be checked with the car hot or cold (I.E. first thing in the morning?)

Thanks!

rsz288

That is a cold setup spec. (IMHO )

Important thing is that when hot, there is still some preload. The AL block grows more than the steel pushrod when it heats up hence more preload is needed when cold.

GM's factory lifter plunger positioning/pre load is targetted to ensure there is still pre load in a very hot engine that has 100k miles+ on it. The pre load caters for production tolerance stack up, wear and metal growth/shrinkage thru hot/cold cycles. And still attempts to provide a quiet self adjusting valvetrain. Which many might say it fails at. At least the quiet part.

White40thGT

iTrader: (1)

So my measurements on a hot engine could be false and needs to be checked on a cold engine, is that correct?

rsz288

Wouldnt exactly say false, but very safe/factory like in terms of never running out of plunger travel. Though if you are running a cam that brings piston to valve clearance onto the tight side, as close as possible to zero lash when hot is the safest in terms of not getting into valve float/seperation and excessive "pump up" if you push the rpm too high. Which you wont right .

White40thGT

iTrader: (1)

I'm just trying to determine when you hear people say that caddy lifters like .060" to .080" preload, if its hot or cold...

rsz288

From memory 0.060" - 0.080" is the factory/stock spec for GM lifters. This range handles hot or cold.

The hot/cold question is around the block expansion from cold to hot, relative to the pushrod expansion. Aluminum expands roughly twice as much as steel.

The factory needs to cater for at least 40 below cold starts through to operating temps that are 220-230F.

GF-4 Oil testing runs at 239F coolant and 302F oil temps, so no doubt GM's upper limit specs are in this range.

So regular operating range of around 270F/150C, and maybe 320F or more with safety margins.

A 212F spread would see the cam to rocker dimension grow 0.020" (lifter plus pushrod), whereas the block/head would grow around double this (give or take).

So the lifter needs to take up an additional 0.020" slack. So to run the preload where the plunger avoids contact with the retaining clip, 0.010-0.020" of clearance at full hot, means a minimum cold preload of 0.030-0.040". Add a little for high mileage wear and production tolerance stack up, and you are at 0.060-0.080" safe.

Crane typically recommends 0.020-0.060" pre load, Comp 875-16 lifters are recommended at zero to 1/8 turn on the adjuster, and they also say 0.002-0.004". Crane is going for a safe factory style spec (very safe in an iron block), Comp is going for an almost zero lash race type spec that minimises "pump up" effects if some valvetrain seperation occurs, and I would guess they mean hot, though they dont say so. If they were done at these clearances cold, they would most likely be a little noisy hot.

IMHO, based on experience, if you are going with your original 1 1/4 turns cold, you will be fine hot, if the adjusters are 24TPI for example, you will have around 0.050" cold pre load, which when you are hot, will mean you are still at ~0.030" pre load.

This minimises the "pump up" lift during any "float", and you should not get near a zero lash situation when hot.

Unless you are pushing your rpm's to where the valvetrain "falls apart" and you have tight piston to valve, you should be fine.

Hope this helps.

White40thGT

iTrader: (1)

Thanks for the explination!

However the 1 1/4 turns was hot, cold it was 2 1/4 turns (roughly .105")

rsz288

Cool! At 1.25 cold you are still on the money .

White40thGT

iTrader: (1)

But it's not 1.25 cold, its 2.25 cold, haha.

rsz288

Yes and you have the option to go back to 1.25 cold.

And currently the plunger has about 0.200" of travel. You are in the middle. It'll work, though if your PTV is close, dont get into valve float. You dont need almost another 0.1" of lift at the wrong time .

DaddySS

For reference, whenever there is a hot or cold alternative the specs are stated that way, if there is no hot spec given, it is assumed to be cold. The preload for LS1s is always cold.

rsz288

Ditto ^^^ with almost any tappets. Though I have trouble with a zero lash cold spec for hydraulics.

White40thGT

iTrader: (1)

Thanks guys.

I went to a shorter pushrod and it fixed all the issues.

XtraCajunSS

iTrader: (2)

I'm glad you got all your issues taken care of. I was wondering if you had checked again cold. Good to see it all worked out!

Shane