HOOK

I am working on installing Crane Roller rockers on my motor. The directions tell me to roll the motor around until the exhaust pushrod starts to rise. Then adjust the rocker arm nut to zero lash, with no lifter preload. Then turn the nut 1/2 to 1 full turn more before tighening the set screw. Zero lash means tighten the nut until you just can't get the last feeler guage in. Is that right? What I am not clear about is the phrase no lifter preload. When the lifter is adjusted to zero lash I assume there is no lifter preload at this point. Is that correct? Now if all this is right I am sure I did the job correctly. My obsevation after the job is that after the all the rockers have been adjusted they are a little loose when the valve is closed. I forgot to check to see if I could get my feeler guage in between the rocker and the valve stem. Is this normal or not. I hope someone can clear all this up for me. Thanks HOOK

jcb999

The best way to set zero lash on a new motor is to tighten the rocker until you can just barely turn the pushrod with your fingers. Make sure the lifters have oil in them. You can pushdown on the pushrod to get the air to pump out.

JakeJr

Let me see if I can help with this.

There are a few different ways to set the valves and any of them will work if the procedure is followed correctly.

The method I've used for over 30 years and the one that is recommended by a few of the big cam companies is the best one I've found.

Other guys may use a different method, and like I said any of 'em will work if done correctly. I just found one that worked for me so I've stuck with it over the years.

Adjusting the valves is not really that complicated, but if you are not use to doing it, it seems that way.

The most critical thing is to make absolutely sure that the lifter is on the base circle of the camshaft lobe that you're trying to set.

There's really no way to see into the lifter valley with the intake manifold on, so what you have to do is watch what one valve is doing and set the other one.

Sounds crazy, but that's the way it's done.

Pick any cylinder, but it's best to start at the front one, say the #1, and work your way back to the last one, then switch sides.

So at #1 you bump the engine over while watching the #1 exhaust valve. As soon s you see the exhaust pushrod begin to move upwards - meaning that the exhaust valve is beginning to open - you stop bumping and set the INTAKE for that cylinder.

When the exhaust valve just begins to open - as evidenced by the pushrod moving upwards - the INTAKE will be on it's base circle.

To achieve zero lash, you slowly tighten the #1 INTAKE nut or poly lock while twisting the INTAKE pushrod between your thumb and index fingers. When you feel a slight resistance, you've achieved zero lash.

This is kind of confusing because that which is a slight resistance to some folks may not be a slight resistance to another.

A better and more fool-proof way is to, instead of twisting, lift up and push down on the pushrod as you slowly tighten the nut. As soon as you can no longer move the pushrod up or down, you've absolutely got zero.

Now is the time to set the preload; once you've established zero. Follow the cam maker's recommendations for this to insure the valve train will remain quiet and the valve will be raised and lowered using the cam's opening closing ramps properly.

Most times this will be one complete turn (360 degrees).

Now to set the exhaust: Continue bumping or turning the engine in it's normal direction of rotation while you watch the intake pushrod.

The intake pushrod should FULLY rise and DESCEND about 1/2 to 3/4 of the way to closing the valve. At that point stop bumping and set the EXHAUST VALVE the same way you did with the intake. Remember, fully open and half way or so closed.

Of course, I'm assuming you're using hydraulic lifters. If your cam is mechanical, then instead of preloading the lifter one full turn, you would use the correct thickness feeler gauge to achieve a slight drag when inserted between the rocker and valve stem.

There are differing opinions on the "slight drag" method. On racing rollers I always used the "Go, No Go" method. If I'm shooting for .020 and a .020 can be forced in but a .021 can't, that's when I'd know it's right. Difference is loose lash plays havoc with the valvetrain in a racing engine.

Hope this helps.

Jake -Not to be confused with my namesake

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1986 Corvette Coupe, 415 CID, Edelbrock 6073s, ZZ9