chasing my tail with tapping lifters

So on my recently purchased z31 300zx I have been fighting a tapping lifter and cant seem to get it to go away. For reference this is what it looks like under the valve covers, with the hydraulic lifters being in the center:

The engine was rebuilt by the previous owner (a fellow GRM'er) and it runs and drives without really any issues except for the lifter noise. The car had sat for a while so i though maybe some of them were gummed up so i added some Marvel Mystery Oil and put a good number of miles on it, still tapping. I then added some sea foam and let it idle and warm up in the driveway before changing the oil, still tapping.

I had a extra set of lifters from some extra head that came wit the car. I submerged them in some oil for over a week. Yesterday I got all the lifters changed out, with none of the old lifters or rockers or anything else showing any signs of wear. all the rockers were tight without any play (as they should be) before i took it apart. everything looks like it was getting oil like it should and where it should. got the new lifters in and back together and... still tapping.

at this point i dont know what else to try. The car shows good oil pressure at cold and warm idle/higher rpm and like i said when changing them i saw zero signs of wear on anything in the valvetrain. The only other info i have is that every now and again when coming to a stop and RPM is dropping down to idle it sometimes wont make any lifter tick for 5-20 seconds then it start tapping again. This isnt every time coming down to idle but occasionally it does, like it's trying to hold pressure and just can and then the tapping starts.

Is there something I am overlooking? anything else i can check/test? time for an LS swap?

So what you're saying is that in only makes noise at low rpms/idle and no where else?

Maybe the oil passage to one of them is [partially] blocked

Time to swap that turbo engine in

LS swap! FTW!

jimbbski wrote: So what you're saying is that in only makes noise at low rpms/idle and no where else?

its definitely prominent at low rpm/idle, when accelerating or decelerating it seems to quiet up, but sometimes at constant cruising speeds (2000-3000 rpm) it will chatter on and off a little.

jfryjfry wrote: Maybe the oil passage to one of them is [partially] blocked

thats what i thought as well which is why i ran the MMO and seafoam through it to try to clean any gunk out, but the oil galley through the center piece that holds the lifters gets its oil from the cam mains/bearings/whatever they are called. I would think if those arent getting oil then there would be some kind of signs of wear and would cause issues on the cam. everything looked like it was well oiled when i took it apart but i guess it could be getting enough pressure at the cam bearings but not enough up to the lifters, stranger things have happened. The question is how would i check that that is for sure the issue and what would the fix be?

and i wouldn't think that it matters but is the NA vg30e engine that was fitted with the turbo parts. these engines are known to have valvetrain noise and i know my xterra with the vg33e definitely did but this is definitely a solid tap/chatter that isnt just typical noisy valvetrain

Maybe its not a lifter noise? Worn rocker or valve stem? maybe the valve seat is worn and causing some binding when hot, collapsing the lifter each lift. Is this a timing chain or belt? worn tensioner on the chain? worn guide?

I once changed all the lifters, rockers, and cam due to an intermittent exhaust leak.

Sounds do funny E36 M3 in engines.

TGMF wrote: Maybe its not a lifter noise? Worn rocker or valve stem? maybe the valve seat is worn and causing some binding when hot, collapsing the lifter each lift. Is this a timing chain or belt? worn tensioner on the chain? worn guide?

its a timing belt so chain noise is out. There were no signs of wear on either end of the rocker or valve stem. it could potentially be a worn valve seat causing the lifter to collapse. it is a pretty freshly rebuilt engine but i dont know the extent of what all was done in the rebuild so the valve seats may still be old. but the noise is definitely high up on the engine in the valve cover area.

Dusterbd13 wrote: I once changed all the lifters, rockers, and cam due to an intermittent exhaust leak. Sounds do funny E36 M3 in engines.

I'm 98% sure it isn't an exhaust leak, ive had 2 ford trucks that both had the typical 5.4 exhaust manifold leak so im familiar with that sound. its a very metallic sounding chatter that sounds pretty much the same as every other bad hydraulic lifter I've ever heard.

but I've been wrong before...

This engine has a distributor right? Have you checked under the cap to see if the rotor is hitting the contacts? worn distributor bearings could be your culprit.

edizzle89 wrote: and i wouldn't think that it matters but is the NA vg30e engine that was fitted with the turbo parts. these engines are known to have valvetrain noise and i know my xterra with the vg33e definitely did but this is definitely a solid tap/chatter that isnt just typical noisy valvetrain

I had an 87 Pathfinder and an 86.5 Hardbody with the VG30. They both ticked at idle. I finally fixed it by selling them. Sorry I'm no help, but it is supposedly common with these engines.

TGMF wrote: This engine has a distributor right? Have you checked under the cap to see if the rotor is hitting the contacts? worn distributor bearings could be your culprit.

never though of that, ill have to check on that.

Dusterbd13 wrote: I once changed all the lifters, rockers, and cam due to an intermittent exhaust leak. Sounds do funny E36 M3 in engines.

I was going to bring this up. The VG engines are known for broken exhaust studs and exhaust leaks. It that should not be intermittent. My neighbors Maxima would do it when cold, but stop once hot.

Tyler H wrote:

edizzle89 wrote: and i wouldn't think that it matters but is the NA vg30e engine that was fitted with the turbo parts. these engines are known to have valvetrain noise and i know my xterra with the vg33e definitely did but this is definitely a solid tap/chatter that isnt just typical noisy valvetrain

I had an 87 Pathfinder and an 86.5 Hardbody with the VG30. They both ticked at idle. I finally fixed it by selling them. Sorry I'm no help, but it is supposedly common with these engines.

yea it still runs great and like i had said didnt show any signs of wear. I have an extra complete vg30et that came with the car so worst case i just drive it as it is and if something decides to let go i can just swap it.

and to be honest an LS isn't out of the question for the future either, especially that there are adapters that will bolt an LS to the FS5R30a trans (used in the late z31's and all the z32's, known to hold up to over 600hp) which is currently bolted to my extra vg30et

I once had a Nissan L20b engine with a valve seat falling out of the head.

The way that I eventually discovered that was the problem was watching and measuring the valve clearance with the VC removed. I had my friend crank the engine with the ignition disconnected while I ran the feeler gages in the gaps. I got inconsistent readings on a couple of intake valves while it was cold, we repeated the test with a warm engine and I didn't even need the gauges to see the problem.

Is it possible to do a test like this with this engine? I know hydraulic lifters won't really be measurable with feeler gauges, but useful observations may still be possible.