Preload

[akadeutsch]

I have been measuring pushrod length and I have noticed that there is a lot of room to move inside a hydraulic lifter. So I started wondering, Why is there so much travel and why should I stick to .020 to .060 preload? Well, I found the answer and I thought it might help others.
With too little preload, the valve train will be noisy and the retaining lock may fail (break or pop out) due to excessive hydraulic force against the retainer. Conversely, too great a preload (more than .060") will produce excessive lifter pump-up, causing the valves to open longer and lift higher, drastically reducing cylinder pressure and hurting engine performance.

[SilverXJ]

You don't want to take up all the travel. Just because you can doesn't mean you should. The further you set the preload the further you compress the spring which will only add to a chance of the lifter pumping up and holding the valves open. That and the oil passages are with a certain area. Change of blocking the oil holes.