Seeking for advise - adjusting hydraulic lifters

It sounds like you've made a mistake; one that I've made myself on my 66 Mustang.  Without oil pressure, hydraulic lifters won't just spring back to their fully uncompressed state immediately. After rotating the crank to make sure the valve is closed all the way, allow the engine to sit in that position for a couple hours to give the lifter time to 'relax.'

Hydraulic-lifter pistons have a very limited amount of travel or preload: .020 to .060 inch. On top, that means approximately 1/4 to 3/4 turn at the rocker arm. When adjusting valve lash, you want the lifters smack on the cam lobes’ heels (valves closed) on compression stroke. But honestly, cam manufacturers offer even more precise advice: Slowly turn the crank until each valve closes completely, then, make your adjustment.

Turn the pushrod with your fingertips while tightening the rocker arm adjustment nut. When the pushrod becomes ever so slightly resistant to your fingertips, turn the adjustment nut 1/4 to 1/2 turn. Though Ford suggests 3/4 turn with some applications, this is too much. If you’re running poly locks, tighten the Allen screw lock. Do this in the engine’s firing order, one cylinder at a time.

You don’t know if you are successful until you fire the engine and it is at operating temperature. If there’s significant rocker arm noise, there’s too much lash and you need to go a little tighter. Some aftermarket rocker arms, such as the Comp Cams Pro Magnum or Ultra Pro Magnum, make a soft clicking sound, which makes a Cleveland sound more like it has mechanical tappets, but is of no consequence.

With roller or flat mechanical tappets, valve-lash adjustment is simple. As with hydraulic tappets, follow the firing order with both valves just closed. Valve lash between rocker arm tip and valvestem is .022-inch cold for both intake and exhaust. When you start the engine, you should hear uniform rocker arm chatter. Any loud clicking is excessive valve lash.

Hydraulic tappets will hydraulically "lock" when the plunger is depressed only 0.005 inch, that's how they are designed. That's why the valves opened when you adjusted the lash. With time they will "bleed down" and the valves will close.

One rule of thumb for adjusting hydraulic tappets is to never compress the plunger more than 1/2 of the plunger’s available travel; however it is important to actually measure the travel of the plunger to verify what it is. The plungers of modern hydraulic tappets do not compress as much as the plungers did decades ago. The plunger travel of modern hydraulic tappets is in the range of 0.060 inch to 0.080 inch. This means hydraulic tappet pre-load should be limited to 0.030 inch to 0.040 inch, and sometimes 0.040 inch will be too much.

There are two ramifications to this reduction in plunger travel:

(1) Even though your engine may be equipped with 100% factory valve train, if it’s using new tappets then the OEM length push rods (8.41 inch length) are probably a bit too long.

(2) If your engine has adjustable rocker arms, you need to measure the tappet’s plunger travel and the thread pitch of the rocker arm adjuster, and calculate how far to limit turning the adjuster to avoid compressing the plunger more than half of its travel.

For Example: The push rod cup style adjuster of a T&D rocker arm has 20 threads per inch pitch, which means each complete turn of the adjuster pre-loads a tappet by 0.050 inch. To pre-load a tappet 0.030 inch would require only 3/5 of a turn of the T&D rocker arm adjuster. Knowing this I would pre-load such a tappet and rocker arm combination with 3/10 of a turn, half of the maximum adjustment (i.e. only 0.015 inch).

Thanks Garth and George for your inputs clearly indicating that I did the wrong thing. I let the engine sit for a day and found that some hydraulic lifters are still hard as a rock. I understood that those need to bleed the contained oil before you should adjust them. I think that as long there is oil in the lifter you do not know in which position the plunger is, right? 

In order to bleed the lifters I have tighten all the adjustment nuts by a couple of extra turns with the results that all valves are now slightly open and thus putting pressure on the hydraulic lifter (valve spring force). I leave this for a day and will check this evening whether all lifters are correctly bleed (show the same "spring effect"). Does it make sense what I'm doing?

Brgds

SIG 

with a feather-duster touch you can feel the point of zero lash on any lifter, pumped up, bleed down or brand new fresh from the box. i prefer to work on completely bleed down lifters so the feel doesn't change drastically at some point when the adjustment meets the plunger oil. IMO priming the engine by spinning the oil pump prior to setting lifter preload is a mistake, there's no need for the lifters to be pumped and causes much confusion.

Success!

The overnight stay with "loaded" hydraulic lifter "oil bled" all of them. They all showed the same soft spring effect. After that it was easy to adjust the lifters. I noticed, when you look now from the side, that all adjustment nuts are on one line. Before there was a significant variation. Before the adjustment the compression tester showed variation of 3 bars between the cylinders which are now down to less than 1 bar indicating that some of the valves were not properly closing. Thank god that I did not burn any of the valves.....

Brgds

SIG