89IROCkid

I'm going to be changing my valve seals tommorow. I'd just like know what is the correct way to set the valve lash on an 89 LB9. The manual says to tighten the rocker bolt until the lifter can rotate rather freely (that's the way they are set now).

Thanks guys,

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Sat "IROCkid" Bimrah
1989 IROC-Z 5.0 L / 5 spd

JakeJr

There are several different ways to adjust the valves and any of them will work if the procedure is followed correctly.

Each guy has his own favorite way, but generally a couple of ways are easier than the others.

What I've been using for over 30 years in all the engines I've built is about the same procedure that is recommended by some of the cam companies like CompCams.

The critical thing in using any of the procedures is to ensure that the lifter is on the base circle of the camshaft lobe.

Since the intake is installed it is very difficult, if not near impossible to see where the lifter is.

So what you do is take it one cylinder at a time and watch the rockers for the that cylinder.

Let's start with the #1, you'd bump the engine over while watching the intake rocker. As the rocker comes to full lift (the valve end of the rocker will be down) and continues on to about half way back up, causing the valve to close, you stop bumping and then set the EXHAUST.

Now you watch what the exhaust rocker is doing and as it just beings to move downwards at the valve end (opening the valve) you stop bumping and set the INTAKE.

In order to determine zero lash, which is the starting point, some folks recommend twisting the pushrod between your thumb and index finger until you just begin to feel a slight resistance. This can be tricky since what is a slight resistance to some isn't to others.

So the procedure I always use is to take the pushrod of the valve I'm trying to set and move it up and down while I slowly tighten the nut or poly lock. When I can no longer move that pushrod up and down, I've found zero clearance.

From that point, zero clearance, I continue turning the nut to the amount of preload the cam maker recommends.

Some guys like to use 1/4 turn, still others like 1/2 to 3/4. GM and others, like TPIS, recommend one full turn after finding zero lash.

Adjusting them with less preload can give the engine a few hundred more RPMs before lifter pump up is experienced, but can cause the engine to be noisy at cold start up.

I always follow the preload recommendation made by the cam company.

Some like to adjust the valves with the engine running and this will work too, but is kind of messy with oil dripping over the hot exhaust/headers. You can get a fire with that procedure too.

To adjust them with the engine running you'd remove one valve cover at a time and while the engine is idling, you back of each adjust nut one at a time until you hear a clacking sound. Now you tighten the nut until the clacking sound goes away; that's zero lash. You'd continue tightening the nut the # of turns you want to use for preload.

Now you'd move on to the next valve.

If the valve train is noisy after you've done all of them, then you may have set one or more of them too loose; if the idle is rough, one or more is too tight.

Hope this helps.

Jake



[This message has been edited by JakeJr (edited October 22, 2000).]

89IROCkid

Thanks for very detailed answer Jake.
I appreciate it.

Might I suggest a tech article on this topic.


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Sat "IROCkid" Bimrah
1989 IROC-Z 5.0 L / 5 spd

ede

easy way i do it when i'm changing valve seals is to use the depth rod on a dial caliper to measure from the top of the stud to the top of the nut and replicate the measurement when i put it back together. if you don't have a caliper a small bolt and double nut would work as a gage to get the correct lash. have also used this method when taking idle and mixture screws out of carbs.

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