How To Adjust Lifter Preload/Lash

There
are several different ways to adjust hydraulic lifter preload and
all
of them will work if they are done correctly. It\’s just that one
procedure is easier than the others, at least for me it is.
The
procedure I use and recommend to everyone asking for instructions
are
essentially the same as those recommended by some of the big cam
companies like CompCams and has been featured in the Tech Support articles
of various auto magazines.
BACKGROUND:
Using the Service
Manual\’s instructions causes you to go from one side of the engine to
the other, you know, bring the engine up on TDC for #1 then set intake
valves #s whatever and exhaust valve #s whatever. You\’ve got to be
absolutely sure you\’re working on the correct valve, too.
Now if
you make a mistake, and believe me it\’s not hard to do, you\’ll set
the wrong valve or the wrong cylinder and then you\’ve got to later
correct it. You won\’t know it\’s wrong until everything\’s buttoned
up, then you\’ve got to tear into the engine
again.
PREPARATION:
It\’s important to loosen all the
preload on the lifters for about one minute if the lifters that are in an
engine have been run before. This allows the plunger inside the lifter
body to rise to the top so that you will have \”true\” zero lash when
you begin your search for it.
Also, it doesn\’t matter whether
the engine is cold or hot when setting
the preload. Hot settings only
apply to mechanical lifters, not hydraulics.
The procedure I
use on the all the engines I\’ve done over the years (and
I\’ve
tried them all) involves simply starting on one side of the engine
at
either the rear-most or front-most cylinder and going straight down
the
line. Front to back or back to front.
For example,
starting with #1, set those two valves, then move to #3, then #5
the
#7. Or you can start with #7 and move toward the front. Whichever way you
choose, use the same procedure every time and on both sides of the engine.
If you start at the front on one side, then start at the front on the
other side too.
Now cross over and set 2, 4, 6 and 8 or 8, 6, 4
2, depending on what you did on the previous side. Go straight down the
line and don\’t skip any valves, just do them in the order that they are
on the engine. This eliminates any chance of missing
one.
The procedure for setting valves involves basically
three things. One of
them is pretty critical and has to be \”right
on\”, that\’s making sure the
lifter is on the base circle of the
camshaft lobe your working on.
That\’s actually what the manual
is doing in the procedure it recommends, insuring that certain lifters are
on the base circle of the camshaft lobes before you adjust
them.
The other two things are you watch what the INTAKE is doing
to set the EXHAUST then you watch what the EXHAUST is doing to set the
INTAKE. (Yea, I know, it seems backwards, but that�s how it�s done!)
Finally, determining \’zero lash\’ and setting the preload. Is that
four?
So here\’s the deal:
Setting the #1: you bump
the engine (easiest if you have a hand held unit or a friend)and watch
what the #1 INTAKE rocker is doing.
The INTAKE pushrod will begin
to move upward (indicating the Intake valve is beginning to open) so keep
bumping until the pushrod reaches full rise then begins to fall about
two-thirds of the way down (toward closing the valve) stop bumping at that
point and set the EXHAUST.
Yep, that\’s right. You watch the
INTAKE to set the EXHAUST, and, of course you would next watch the EXHAUST
to set the INTAKE.
Here�s where I differ from some of the articles
I�ve read. They recommend twisting the pushrod between your fingers while
slowly tightening the adjusting nut/polylock until a slight resistance is
felt with your fingers. This is the spot that gets some guys into
trouble. What exactly is �slight resistance�? Slight resistance to one
person may not be to another.
So instead I prefer and recommend the
UP AND DOWN METHOD. Once you�ve got the lifter on the base circle of the
cam lobe (which is what we just did by doing all that \’watching�, now
take the pushrod between your fingers and move it up and down as you
slowly tighten the adjusting nut/polylock. When you can no longer move
the pushrod up or down, STOP! You�ve just located zero lash.
Now
set your preload. Some guys like quarter turn, other half turn, still
others three-quarters turn and some, like GM and TPIS recommend one FULL
turn. Choose your own poison here.
Less preload (1/4 turn)
supposedly gives you a few hundred more RPMs up top; meaning the engine
will rev a little higher before the hydraulic lifter pumps up. The
downside is that the valvetrain may be a little noisier at low
RPM.
If you have a mechanical cam, get out your set of feeler
gauges and back off the
adjusting nut until you can just barely get the
correct thickness gauge
between the tip of the valve stem and the
rocker arm. A slight drag is what you\’re looking for here. Leave the
adjusting nut there or lock down the setscrew of your polylock at that
point.
So, what you\’re doing is watching one valve and
setting its mate.
Watching the INTAKE pushrod tells you when the
EXHAUST is on its base
circle and watching the EXHAUST pushrod tells
you when the INTAKE is on
its base circle.
Now move to the
EXHAUST on the same cylinder.
Bump the engine until the EXHAUST
pushrod just begins to move upward. STOP! You�ve just found the base
circle for the INTAKE. Now use the UP AND DOWN METHOD and when the INTAKE
pushrod can no longer be moved up or down you�ve found zero lash. Set
your preload.
Do that for the remaining cylinders right on down
the line and you\’re done.
The preload adjustment is rather
forgiving as you can probably tell by the
wide range of adjustments you
can use (1/4 to 1+ full turn). Basically what you�ll be looking for is
for the lifter plunger to be depressed about .030�, +/- .010. One half
turn will almost always give you the desired .030 plunger depression and
proper preload.
Which preload should you use? I always follow the
cam maker\’s recommendation.
I know before I sign off that there
are others who have procedures that they like better or may have a
slightly different way of setting the exhaust (for example instead of
letting the intake valve pushrod drop half way down, stop when you first
see it start to move downwards or even to let it drop all the way down).
Well, to each his own.
Letting it drop 2/3 of the way down
insures that you passed the point of valve
overlap (when both intake
and exhaust valves are open at the same time).
On street type cams
the overlap is relatively short so both valves are not
open at the same
time for very long, but on racing camshafts, that event
is much longer
so you have to wait until the intake valve is 2/3 or more toward
being
closed before you set the exhaust. Otherwise your exhaust won\’t be on
its base circle and will still be on its closing ramp, see what I
mean?
As with procedures I use for finding TDC for #1, changing
all the engine bearings with the engine in the car, installing an intake
manifold so it won\’t leak, etc., this has worked for me over the
years.
Next time you\’re at a NHRA meet watch the procedure
the �Big Boys� use between rounds. I�ll bet you�ll see them using the
same procedure.
Just trying to help.
Jake