[2old2fast]

Sometimes when setting up new lifters they will bleed down and you have to leave them sit for a bit and they will eventually will pump back up and tighten back up to your lash setting. I wish I could explain more but I have not really had that problems with setting up hydraulic lifters over the years but I have had where first setting them the rocker arm was loose enough I could wiggle it some when set but after rotating the engine over while setting the others and then I went back to check them they were tight after that and correctly set.

Make sure you do the pushrod moving up and down method and not spin it with your fingers as you can get a false zero lash feel if your new to doing this.

Unless the engine is producing oil pressure , neither a lifter or anything else is going to " pump" up . There is an internal spring in thee valve lifter that will return the plunger to the top , if it does not , either the lifter is defective or has debris in it IMO