C5 Tweaker

I am baffled by my calculations and observations as compared to "rules of thumb" regarding lifter preload.

Depending on lifters, configuration, and who you ask, preload should be somewhere in the range of .025" to .080" (.050" nominal). The "rule of thumb" appears to be 1.5 to 1.75 turns from zero lash.

I calculate the preload as follows:

.50T = .039"
.75T = .058"
1.00T = .078"
1.25T = .098"
1.50T = .117"
1.75T = .137"
2.00T = .156"

As the numbers did not jive, I measured it with a dial indicator on the rocker at the pushrod centerline. It matched the calculation precisely.

Calculation is as follows:

Thread pitch = 1.25mm = .0492"
Ratio = 1.7
(1 Turn x 1.7) / 1.7 = 1.588 multiplier

Thus: 1 Turn x .0492 x 1.588 = .078" Preload

This leads me to believe I want about 1 'turn' of preload rather than the 1.5 to 2 I frequently read.

Am I missing something?

<small>[ May 23, 2002, 08:40 PM: Message edited by: C5 Tweaker ]</small>

FastOrange99Z

I have always gone 3/4 to 1 full turn past zero lash, never more. Id say more is no good. You may need to shim the rocker to get the correct preload.

C5 Tweaker

MTI says 1.5 - 1.75T

Crane instructions with their 1.8 rockers indicates 2 turns (or .153" preload with 1.8 rockers).

Crane tech support says .060"

What the heck?

NoGo

iTrader: (2)

I actually asked Crane tech support this question yesterday. It is 3/4 turn past zero lash. Any more than that and you have to shim your rockers to get the proper preload.

cantdrv65

iTrader: (3)

It sounds like it is no different than the old SBC. I set my lifters at 1 turn when I used Rhoads lifters on my old 331 high school Monza. I'd bet 2 turns would be asking for a collapsed lifter on an Ls1.

C5 Tweaker

I noted that the Corvette Fever article also stated 2 turns with 1.8 rockers. The instructions with the rockers say the same. The generic lifter instructions on their site say .020 to .060 preload.

I called Crane to ask what is up. They said their LS1 lifters 'like' .060, with .040 being the minimum and .090 being the maximum. I asked about the .153" "2-turn" instructions. He dismissed them and said they were only written for the initial vendor that was doing the development. He went on to say that preload over .090 can result in pump-up and float.

It looks like Crane 1.8 instructions proliferated to result in a misinformational article in Corvette Fever.

MelloYellow

I finally understand all this.

Any more comments?
ttt

TRYMYZ

iTrader: (2)

Someone please correct me if I am wrong, but I thought, with stock lifters, you just tightened the rockers down to 22 ft lbs. If I am wrong please instruct me on the proper way to do it.

Thanks
John

NoGo

iTrader: (2)

You can get away with just torqueing (I have a couple times) but ensuring proper lifter preload is "the right way". Its easy to do anyways, 3/4 turn past zero lash.

By just torqueing you run the risk of collapsing a lifter, damaging a lifter, excessive valvetrain noise, and not getting the most out of your car.

TRYMYZ

iTrader: (2)

Ahh. Thanks for the info. So what you normally do is turn the bolt until the pushrod no longer turns or moves, then go 3/4 s of a turn past that ?

MelloYellow

Someone on another forum has mentioned that 'stretching' of the rocker bolt can throw of preload/turns measurements and makes counting turns invalid.

Comments?
ttt

jmX

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by MelloYellow:
<strong>Someone on another forum has mentioned that 'stretching' of the rocker bolt can throw of preload/turns measurements and makes counting turns invalid.

Comments?
ttt</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">At 22ftlbs I really doubt much stretching of any bolts happens. I dont buy that theory.

roy

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by TRYMYZ:
<strong>Someone please correct me if I am wrong, but I thought, with stock lifters, you just tightened the rockers down to 22 ft lbs. If I am wrong please instruct me on the proper way to do it.

Thanks
John</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">John you are correct.

For everyone else out please explain how you are adjusting your preload. The LS1 is not like the old SBC where you set preload with a locking nut on the rocker stud.
The only way I see that you will adj preload on the stock LS1 rocker is with shim stock between the rocker arm and the pedestal on the head .

Please by all means correct me if I am wrong.

Fireball

iTrader: (21)

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by roy:
<strong> </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by TRYMYZ:
<strong>Someone please correct me if I am wrong, but I thought, with stock lifters, you just tightened the rockers down to 22 ft lbs. If I am wrong please instruct me on the proper way to do it.

Thanks
John</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">John you are correct.

For everyone else out please explain how you are adjusting your preload. The LS1 is not like the old SBC where you set preload with a locking nut on the rocker stud.
The only way I see that you will adj preload on the stock LS1 rocker is with shim stock between the rocker arm and the pedestal on the head .

Please by all means correct me if I am wrong.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Either by use of shims by changing pushrod length

roy

Thanks FireBall. I thought Iwas going crazy for a second.