Raise

iTrader: (31)

i did a search but i didnt ever really find what "preload" actually means. i hear it referred to in the same sentence as cam and lifters, but i would like to know what exactly it is.

PREDATOR-Z

Hmm, lifter preload is the amount of preset pressure on the lifter cup/spring assembly that is necessary to maintain adequate constant contact and force on the pushrod/lifter/cam lobe assembly.
This variates with different lifters and usually is between .045>.090 on stock lifters.
Too much preload and the lifters will "pump up" and can lead to lifter failure, too little will result in excess clattering and possible valve float from not maintaining constant contact.

Raise

iTrader: (31)

so do lifters have preload already set in them or is it set when u put a pushrod and a rocker arm on and tighten it down?

Cal

iTrader: (1)

The preload for a LS1 has to be designed into the length of the pushrods, since they do not have adjustable rocker arms. Reasons for it to change are a cam with a smaller than stock base circle, and milled heads. You should get 1/4 to 3/4 of a turn on the rocker mounting bolt when the preload is correct.

PREDATOR-Z

No.
That is why there is 2 kinds of rockers.
1- adjustables
2- non adjustables

A- adjustables > lifter preload on these will variate from one manufacturer/design to another and install manual specifications should be followed after 0 lash. This can variate between 1/8th to 2 full turns.
B- non adjustables just tighten them down to 22lbs/ft and go to town. this is where proper or should I say the closest p-rod length needed is more critical.