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Old 02-18-2004, 01:40 PM
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When doing the static type of adjustment, Its best to back the nut off some to make sure the pushrod and lifter plunger is totally unloaded.

Hydralic lifters have a spring under the plunger to keep it pushed up against the snap ring when not under any load. What Crane and Comp want you to do is to make sure the lifter is on the lowest part of the cam lobe, then slowly rotate the pushrod with your fingers while tightening down the rocker nut. Once you feel the pushrod start to drag, turn the rocker nut to their specs, usually 1/8 to 1/2 turn.

The 7/8 turn you mention sounds pretty scary if it is indeed that far down. The 1/2 turn is to give the lifter some margin of automatic adjustment as things wear. If you tighten them too far, its possible that you will compress the plunger inside the lifter all the way down and the valve will not close completely, resulting in really bad performance and low/no idle vacuum.

The preload, for the most part, does not affect the overall lift of the cam. It just gives the lifter some working room. If you do happen to over rev the engine, the lifters will usually "pump up" ( the oil fills the lifter all the way up including the preload distance) and the valves will float, as in not completely close. This can be a good thing as it will keep the engine from going balistic and making a mess in the street. Also, if you over rev the engine, the springs will probably not be able to keep up and that will limit the rpms too. Most stock lifters and valve springs will "float" around 5 grand, which is pretty high for most stock engines.

If you are building a performance engine and are expecting to rev higher than stock, then you will want to use "anti-pump up" lifters and valve springs that are rated for higher rpm use.

Mark

Last edited by Jmark; 02-18-2004 at 01:49 PM.
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