I know this is basic, but need some help. Reading up swaping my heads and am trying to understand how you measure and make sure your push rods are right.

Thanks

 

If you are using an adjustable pushrod, then you adjust the pushrod length until you reach zero lash. Zero lash is achieved when the pushrod rod is just long enough to take the clearance out of the valve train with the lifter on the base circle of the cam. The old method is to spin the pushrod but I never could get that right, and with an adjustable you chance changing the length. I install the pushrod and the rocker and snug the rocker (you don't need to tighten to the full torque value, rather ensure it is properly seated). Then gently lift the rocker tip at the valve. If you get a "tick" "tick", the pushrod is too short. If a gentle lift get no "tick" "tick" the pushrod is too long. Either way, adjust the pushrod length and try again until you just get rid of the "tick" "tick" or it is barely "ticking" when you lift the rocker tip. Sometimes you can adjust the pushrod in place with your finger tips without it spinning so you don't have to keep taking it apart.

 

Thanks for your response. I'm still a little confused, but I've also never done this before or "messed" with a valve train before. You learn a lot by doing.

 

Here's another way to look at it. Lift the rocker up at the valve. When the pushrod is too short there will be a gap between the rocker and the tip of the valve. At zero lash, that gap has been just closed.

Here's another way. In a hydraulic lifter there is the outer body and then inside the opening at the top is a clip in a groove in the body. Under that clip is a cup where the pushrod sits. The clip holds the pushrod cup inside the lifter body. As the lifter compresses the cup is bushed down inside the body and you get a space between the cup and the clip. Zero lash is the point where the pushrod just barely starts to push the cup down into the lifter.

You have to be careful you do not compress the cup down into the lifte until it bottoms out and call that zero lash. This is usually very easy to do with new hydraulic lifters. Zero lash is when the cup just begins to compress, not when it is bottomed out in the lifter.

Zero lash is always set when the lifter is NOT on the lobe of the cam or when the valve is supposed to be closed. A general rule is 1.5 cycles past the valve opening cycle.

Intake valve
Turn through the intake stroke, bring piston to top of compression stroke and about 1/2 down the power stroke. If you are turning the engine and the exaust valve for the same cylinder just begins to open, then stop turning and adjust it there.

Exaust valve
Turn through the exaust stroke, bringing piston back down through the intake stroke and about 1/2 way back up through the compression stroke. If you turn the engine until the intake valve on the same cylinder has closed then you can go a little further and then stop turning and adjust the exaust valve there.

Doing the above will put the lobe on the cam about 1/2 a rotation away from the lifter and ensure you are on the base circle of the cam.

Peter

 

In it's simplest terms, zero lash means taking all the "slop" out of the valvetrain when the valve is CLOSED. The lifter is on it's lowest part of the travel (the base circle of the cam lobe). Solid lifter valve trains need some "slop" in them cold but hydralic valvetrains are set at ZERO lash cold. The lifters take up any clearance needed during normal running of the engine.

 

No.

Zero lash is for measuring pushrod length purposes only. Once you determine that base length dimension (at zero lash), you then add your desired lifter preload dimension to arrive at your correct pushrod length.

If you set it up with zero lifter preload, it will be just as noisy as a solid lifter engine.

 

Zero lash means zero clearance between the lifter, pushrod, rocker and valve. Preload is the amount "tighter" than zero lash. Zero lash is not just for measuring pushrod length (e.g. if you have adjustable rockers and a hydraulic valve train), IMO.

For example, when setting a hydraulic valve train, you tighten the poly-lock until you hit zero lash, and then go half a turn tighter (or whatever the cam company tells you to do) to set the preload.

Here's what Roger Vinci (Vette owner, life long performance guru, valve train wizard and all around good egg!) has to say:

 

Thanks Turbo, always solid info.