We have a customer car here with an engine that has hydraulic lifters.
They are loud. The adjustment when the car arrived was less than half a turn beyond making contact.
We've also run the engine with the adjusters turned in half a turn and at 1 1/2 turns.
It may be a little quieter at 1 1/2 turns but still much louder than solid lifters set with .006 lash.
My question, and we should be able to verify this easily, is:
If the heads have heavy duty valve springs, would the lifters be unable to pump up properly and be noisy?

Required reading...
http://www.ratwell.com/technical/HydraulicLifters.html

After reading:
Adjust all valves like a solid lifter motor (0.006). Run the motor, short drive is better than just idling/reving, if possible. Check all the rockers again. If ANY of the lifters can be compressed even slightly by hand then they aren't pumped up. Leave the adjuster loose on those and adjust all the 'hard' lifters to the correct spec. Rerun and reassess and repeat until all the lifters pump up.

To more directly answer your question, there is a check valve inside the lifter that makes it incompressible once pressure is applied. HD Springs can't overcome this system (aside from breaking something). So HD springs aren't part of the equation. The lifters just haven't pumped up.

I've usually have to do at LEAST 3 rounds before they all pump up, but 5 or 6 rounds isn't unusual. Some bubbles are quite stubborn. This process is kind of like bleeding brakes. It takes way longer than it seems like it should to get all the bubbles out. I've only done the process in CA, but I suspect thicker/cold oil will make it take longer.

I have heard of people dunking the lifters in a container of oil, then using a pushrod to press on the end of the lifter to try to purge bubbles out. Don't know if that actually has any effect besides psychosomatic, though...

--DD

Works with new lifters to get them partially filled. But you can also just pull the caps out and fill them directly. It doesn't work 100% because the 'press on the end' part ends up shutting the valve. You really need pressurized flow throught the lifter to carry away the bubbles.

Different era vehicle but same basic design, my Vanagon 2.1 takes plenty of time to get quiet and run smooth if the lifters have leaked down.
Regular use and clean oil make a difference.

https://www.youtube.com/watch?v=7lrAcJ67b78


Pull the pressure down to remove air from the lifters before installing.
Vacuum bag them in oil,no disassembly needed.

I had a 2.0 with hydro lifters and currently have a Vanagon as well. In both cases they would always bleed out if left sitting for a while, the older they got the worse this problem seemed to become.

Sometimes after sitting all winter they would absolutely refuse to pump up. My solution when this happens was to buy some cheap lightweight oil (usually 5w30 or lighter, cheap stuff because you dont use it long) Do a complete oil change to the lightweight oil and add a small amount of ATF to help clean things up. Run the motor up to temp and I could usually get the lifters to pump up and stop clattering within 5 or so minutes, you may have to rev it/drive it for a bit to build pressure. Once they are pumped up and quiet, oil change again to your regular weight oil.

Works the same as entrapped gas in your brake lines,the gas rises to the top,being lighter and is trapped there,compressing and expanding as the system pressure changes.
Same thing happens to fuel lines too,vapour lock.
The solution is a fine edm hole in the body of the lifter,strategically placed to allow the air to bleed out while starting,small enough to not affect the running pressure when hot.
The oil feed holes may have to be enlarged to compensate for the larger flow volume.

I have nothing to add regarding the OP's question, just want to remind folks that that ticking is the sound of the valve train beating itself to death. Run too long - and/or with elevated revs - in that state and eventually something will give. In these engines (and some others) it is very often a valve seat. It is akin to running a solid lifter valve train with massive amounts of lash.

I hate hydraulic followers in these engines.

Interesting that the 993 motor does not have this problem.

I have a 90 Vanagon and sometimes a lifter bleeds down causing racket. Once it runs a while above 3K rpms it pumps back up and is quiet again. Usually happens after sitting for a week or more with no activity.

Seems a lot do this.

They could just plain worn out or not pumping up properly due to blockages.
In other engines 2 oil changes with cheap oil normally bring them back,never had any luck with the atf treatment however.
I don't recommend engine flush treatments,on several occasions I have seen this additive make the problem worse....permanently.
Always expect some rattling on startup,good lifters will still do this in an older engine for a short time then clear especially when the engine is reved up.

.
Very different arrangement in a 993
The "hydraulic lifter" in the 993 is actually incorporated in the rocker arms.

Problem solved.
We deleted the secondary relief valve in the oil circuit, based on the fact that hydro cases didn't have that feature according to the Ratwell site.
The lifters quieted down very quickly.

I know that you can, but does it have to be an EDM to make the hole? Don't have the lifters but I have the jewelers drills.

Tough to drill even with solid carbide due to the hardness of the lifter body.
A fine drill of 2 hairs diameter,0.15mm,.006" while capable of drilling soft materials of thin substrates would have a difficult time at that depth/dia ratio.
The spindle speed used is 60K,a specialized drilling machine,air bearings,high frequency ac motor,sounds like a jet.
edm,into the chamber,the leakdown rate smaller than the pumpup by pressure feed.
The purpose is to allow the gas to escape while maintaining prescribed pressure.
A leaky checkvalve in a lifter positioned vertically will do the same thing,allowing the gas to escape,
while the oil,of much greater viscosity will not have the flow rate to affect normal operation.
Horizontally,the bubble remains trapped at the top of the pressure chamber within the lifter body.
Give it a place to go and it will.The oil,if not changed frequently will gum the holes eventually.
This edm process is not cheap,used primarily in injection mold,die making,and aero work in exotic materials.
Some new tech uses laser,plasma and even electron beams in a vacuum chamber.
A larger hole drilled then plugged like a carb jet would work as well,only if you're certain the plug stays put.

/

That should have been done when the engine was built, with hydraulic lifters.

A hydro T4 engine with HD valve springs is whats known as a "mechanical oxymoron".