There has been many posts regarding hydraulic valve lifter lash adjuster (lifter) morning startup noise or permanent noise (ticking). At this time am porting cylinder heads for my new engine and it would be nice idea to check all the lifters before reassembling the head back together.
Member Mike H(AzHeat) had the same problem with some of the lifters being shut open. I whanted him to spend some money for new ones at the time so I did not mention this procedure to him, but I will defenetly send him the link of this post. LOL. Here is his post about his problem:[[ http://www.twinturbo.net/net/viewmsg.aspx?forum=technical&msg_id=875507 ]] That is scary, his machine shop told him they are overpumped???!!! I would not let those guys touch anything of my car. The lifter should go to its base position right after there is not pressure when the car is turned off, the pressure bleeds back out passed the check ball, so he either has check ball stuck in dirt or those holes are plugged up. When inspecting a lifter it should feel the spring resisting the movement by pressing the lifter with fingers, if its rock solid that means the regulator plate holes are plugged up with dirt or carbon inside the lifter or same with check ball. When this happens the lifter either can’t get filled with oil or its full with oil. Normal operating lifter will always be half full of oil inside its plunger when engine is shut off. Soon as the engine starts running and oil pressure builds up the lifter regulator plate holes need to be %100 clean in order for the lifter plunger to fill up fast with high pressure of oil and provide noise free operation. Now if the tiny hair size holes are plugged up the plunger will never get filled with that high pressure oil and it will fail to extend it self resulting in faulty lash clearance and ticking noise will exist.
Those two tiny holes can get unplugged by using some engines oil detergent additives like marvel mystery oil or others, that’s only if you are lucky. Z32 lifters are made of very hard material and its hard to find one that wares out so they are definitely reusable, they only need some good cleaning and they will work like new again and as long as you change oil often they will never plug up again, use marvel mystery oil it’s a good product.  Here is how you take it apart. Hold the lifter in hand and tap it few times in a open vise and watch for the plunger to pop out, hold your hand under it so it drops in your hand.
Inspect the parts for ware and soak them in the barryman fuel injector cleaner solvent, you can get that in AutoZone, that cleaner will dissolve varnish from the parts. Check the plate holes to see if they are not restricted, also inspect the check ball for free movement.
Put the plunger back together, put some oil on it and just pop the lifter body over the plunger, you should be able to hear the snap ring seat itself in, soak the lifter in engine oil for 5 minutes and its ready to go back in the cylinder head, all like brand new. 
Oil pressure comes in the main feed hole, some of it goes out to lube the cam lobe and some of it fills the lifter plunger which will expand and give the engine maximum valve lift for best performance, if you have half clogged lifter the engines power might suffer. VG30 is critical with cylinder power balance, if one valve does not open %100 when you get on WOT and that cylinder is falling behind the others in power output, the engine and power will suffer because it will get out of its balance especially in high revs. 
Just take a look how small those holes are, they can get plugged so easy if the oil is not changed often. 
This is a first time someone mentioned the lifter maintenance here so I think its a good post for FAQ section, I think every member here had valve ticks on engine.
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How to rebuild a hydraulic valve lifter for Z32 FAQ - 
