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).

Checking Lifter Preload- From Katech

1) The only way to properly check (and know where you are in the travel) is
to use a special checking lifter or completely compress a stock lifter.
a) Checking lifter consists of a lifter that has been disassembled
to install shims that lock the plunger at the top of travel in the lifter body.
If using this method you would add length to the checking pushrod to put the
final pushrods into the middle of travel of the plunger.
b) Using a stock lifter, you must make certain that you have pumped
all the oil out of the lifter. To do this leave it at valve full open (highest
spring load) for a while with an indicator on the pushrod side of the
rocker. Watch to see when the indicator stops moving (when the plunger is
fully compressed in the lifter body). Once you have compressed the lifter
rotate the engine to close the valve, extend your checking pushrod to full
length. Using this method you will subtract length from your checking
pushrod to put the final pushrods into the middle of travel of the plunger.

2) Typical plunger travel on Gen 3/4 lifters is 0.150 - 0.200 depending on
the manufacturer, year, etc. We recommend 0.075-0.100" from the bottom of
travel (using method 'b' described above) or 0.075 from the top of travel
(using method 'a' described above). That will generally put you close to
the middle of travel. While there are many different strategies for where
to put the plunger, for street use we strongly suggest that near the middle
of travel is the safest for durability.

3) The more precise method of checking is 'a' because you are not guessing
that you got all the oil out.