I found the following on the Crane Cams website regarding lifter perload in the LS1/LS6 engines. I should also say that it was prefixed with a pitch to sell their adjustable rock arms. However it does make a lot of sense.

I have found numerous posts here regarding the topic of lifter preload so I thought some of you might be interested in this article. I will personally be putting a new cam in my car in the next few months so I was looking for information and found this topic.

Start of article follows:

LS1/LS6 Engines: Lifter Preload And Its Affect On Valve Spring Life!

Chevrolet’s LS1/LS6 engine family has gained wide usage in most all 2000 to present GM light duty trucks, as well as the Corvettes and Camaro/Firebirds. Some aftermarket manufacturers are recommending setting the hydraulic valve lifter preload at .004-.010” (hot) for maximum performance applications. Many tuners and enthusiasts are not paying attention to the “(hot)” requirement for this lifter preload. This little bit of negligence is wreaking havoc with all LS1/LS6 valve springs. Two problems exist. First, trying to set preload on a street driven LS1/LS6 with the engine hot is next to impossible. The engine will cool down before you can get the coil packs and the valve covers off. Second, the automotive engines feature aluminum block and heads, and the trucks feature iron blocks with aluminum heads. The aluminum engine castings expand more than twice as fast as the steel valve train components. If a tuner or enthusiast sets the lifter preload at .004-.010” with the engine cool, by the time the engine comes up to operating temperature, there will actually be .002-.008” of valve lash in the valvetrain. The hydraulic roller valvetrain has no clearance ramp to take up this lash and, as a result, the lash causes a hammering action to take place in the valvetrain. This has a devastating affect on spring life and strength. In addition, it creates a great deal of noise that causes the knock sensor to retard timing (unless the knock sensor is disabled), resulting in a loss of power and higher than normal engine temperatures.

Lifter preload settings of .004-.010” have been recommended for years (by many aftermarket cam companies including Crane) for maximum effort applications with flat tappet hydraulic valvetrains, but extensive testing at Crane Cams R&D Department has proven conclusively that hydraulic roller lifter valvetrains operate best with .050-.080” of lifter preload. These is no sacrifice of low-end power, and the power holds on beyond the power peak much more noticeably. We have expressed this in previous newsletters, and several magazine editors and independent tuners have corroborated our findings. It is our opinion that improper (inadequate) lifter preload is one of the major causes of valve spring failure (regardless of manufacturer and spring design) on LS1 engines (especially because of the significant thermal expansion properties of the aluminum engine castings).

 

This is most of the issue with Comp R's folks don't understand that an aluminum block grows, so they set .010 preload cold which grows .010 or so when hot, so you end up with 0 preload, or in some cases some positive lash just like a solid roller. Hence the noisy valvetrain, and broken lifters...

 

To add to J-rods..If you have the comp R's to tight and they will blow apart..They are the biggest POS's I have ever worked with. Way to sensitive for our applications.

Stick with stockers if you spinning less than 6800ish. If you need more headroom go with the Morel lifters. They have the same preload range as stock.

Phil

 

What's considered "too tight"? Comp suggests 1/8 turn of the locknut as sufficient preload.

 

WOW!

 

This hits right at home. I just finished my h/c. GM asa cam and heads(milled .055)
and now my car sounds like I have a valve tap or loose rocker. I have 7.350 pushrods. Is it possible these are to short? How do you check the "hot" preload?

 

Stock block?
Gasket thickness?
Base circle of ASA cam?
Stock rockers?

What I did was to use the following as the baseline for my measurements.

Baseline................................ ..........New Setup.....Difference


Stock Cam Radius.... .759 ********** .6825 ***** .0765+

Stock Gasket........... .0523 ********* .054 ***** .0017+

Heads Milled........... .00 *********** .020 ***** .020 -

Stock pushrod........ .7380 ?? ***** 7.40 ******* .020 -

Deck Height.......... 9.235 ******** 9.235 ***** 0.00

Spring Height....... 1.80 ********** 1.80 ****** 0.00

Net result.................................. .............................. 0.0382+

So the way I see it my 7.4 rods are a little short as compared to my base setup.

A couple of unknowns.

Is the stock pushrod 7.380?

What does GM set the factory preload at?

I think my next step is to just get adjustable rockers and quit worrying about it.

 

I dont know the base circle on the cam,
Stock rockers
.054 on the GM gaskets

 

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