ok, i've had the car(74 Z-28, 383) for a little over a year now. up until a few weeks ago, whenever i got on the throttle almost all the way, i could hear a barely-audible sound of what im thinking was the rocker arms(slight tapping noise and very fast sounding). so, recently, whenever i get the pedal half way down i hear it... is this a problem? also, i've heard the term 'zero lash' for quite a while now. does this relate? thanks for the help

 

sorry, didnt see paul holmes article which was exactly the same subject as this.. so, to narrow my quesiton down, is there any danger if they tick and i continue to drive it? this has only recently become a concern because my daily driver is shafting itself(running on 3 of 4 cylinders, and please dont ask what kind it is... i know i deserve a beating, but it was my first car which was not really my choice of what i was getting), so i have to drive my real baby back to college since spring break is almost over(its 2 hours away)---also, i dont drive it that hard either

 

MTX,

Are you sure what you are hearing isn't detonation. In my 84 Z, that's what it sounds like, a rocker out of adjustment. I pulled the valve cover to check, and found one rocker that wasn't right, fixed it, and still had the problem.

But detonation sounds just like valve "clatter" in my car. What ever it is I'd do some exploring.

Here is what someone sent me once explaining how to adjust your lifters:


IP: Logged
JAKE
Senior Member
From: DESOTO, TX, USA (Just south of Dallas)
Registered: Feb 2000 posted 03-11-2000 03:57 PM

There are several different ways to adjust valves 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.


Using the 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 and you
can 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.

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 fore-most cylinder and going straight down the
line.


For example, starting with #1, set those 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 everytime 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 you cross over and set 2, 4, 6 and 8 or 8, 6, 4 2, depending on what
you did on the other 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.

So here's the deal:


Lube the bottom of the lifters with moly paste and install all the
lifters, pushrods, rockers and nuts and leave everything loose.
Setting the #1: you bump the engine (easiest if you have a hand help
switch connected to the 12V and "S" terminal on the starter)and watch what
the exhaust valve is doing.


When the EXHAUST pushrod just begins to move upward (indicating the the
exhaust valve is just beginning to open) stop bumping and set the INTAKE.
Yep, that's right. You watch the exhaust to set the intake, and, of
course
you would next watch the intake to set the exhaust.


Screw down on the nut or polylock while at the same time twist the pushrod
for that valve with your fingers. As soon as you feel slight resistance
you know that you've taken up all the slack, now set your preload
according to what the cam maker's recommends.

Another way, which by the way is a lot less prone to error, is to use the
lifting method. Instead of twisting the pushrod, lift it up and down.
When you can no longer lift it up or push it down, that's zero lash.

Using the twisting method you're suppose to feel for a slight resistance
and when you do feel it you know that you have zero clearance. Problem
is that what seems slight to one person doesn't to another. So the up and
down method is easier and when you can no longer move the pushrod up or
down, you've got zero.

If you have a hydraulic lifter camshaft, set the preload now. If you have
a mechanical cam, get out your set of feeler gages and back off the
adjusting nut until you can just barely get the correct thickness gage
between the tip of the valve stem and the rocker arm.

On hydraulic cams some guys vary from those settings and use 1/4 turn,
some
use 1/2 turn, still others use 3/4 and some even use one full turn as is
recommended in the service manuals. I always use what the cam manufacturer
recommends and in the case of the ZZ9 hydraulic roller that I'm running
TPIS recommends 1 full turn of preload after finding zero clearance.


The less you preload the more rpm capability it's suppose to give you
before lifter pump up. Downside is that you may get ticking noise due to
the lower preload setting.


So, what you're doing is watching one valve and setting its mate.
Watching the intake pushrod tells you when the exhaust is on it's base
circle and watching the exhaust pushrod tells you when the intake is on
its base circle.


Now move to the intake on the same cylinder.
Bump the engine until the intake pushrod rises to it's maximum height
(intake valve fully open) and then begins to drop back down (valve
closing). When that pushrod is about half way down, stop and set the
exhaust using the same twisting/lifting procedure as with the intake.


Do that for the remaining cylinders 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).

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). Well, to
each his own.


Letting it drop half 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 relative 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 til the intake valve is half way 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 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.

 

thorough response, and really clears up some questions i had. so, zero lash is the amount of clearance, or, no clearance, between the rocker and valve? so i guess ill run down to the gas station and fill up on 89, or 93? octane to see if that eliminates the sound i hear(run 87 in it now, the guy i bought it from said that he usually put 87 in it, but every now and then would use 93... why, i duno, but thats what he did). if not, then it isnt detonation, and as far as i know, that only leaves the valvetrain to be the culprit.