Tapping coming from under valve cover (not lifter tick)

[Aphix]

I definitely noticed an improvement once the oil was changed. It was no longer consistent but harder to coax the engine into knocking

 

[Aphix]

Comp test brought back 100 psi and a little under 120 psi on the two cylinders near the tapping. I'm assuming this is a worn cylinder which has led to piston slap?

 

[Calan]

Comp test brought back 100 psi and a little under 120 psi on the two cylinders near the tapping. I'm assuming this is a worn cylinder which has led to piston slap?

Possibly.

Regardless, those are some really low numbers if the comp test was done properly. If they are accurate, it's time for a rebuild.

FYI - Assuming you are on the stock 7-bolt... the standard value should be 178psi, and the service limit is 133 psi.

 

[Aphix]

Yeah thats why I was questioning those two cylinders. I had the head hot tanked along with a leak down test and resurfaced about 1k miles ago. I should have measured the cylinders while it was off dammit.

 

[Aphix]

I did another compression test and came back with cylinders all between 155 and 180 which was a nice surprise. I have been busy with school so the car has been doing a lot of sitting. Anyways I got it back out last weekend and drained some more lifters from the intake cam side and was able to get the tap to stop for about a minute, and then it came back. I kept swapping out those three lifters I had just drained and couldn't get the car to react differently to it.

It got me thinking, I have been having an issue with my oil sending unit for awhile now, it was giving me really uneven readings, so I threw a different one in from U Pull It and it seemed to help; but I noticed that pressure was low at idle, but great when the engine was revved up. And then I got to thinking about how the tap will happen immediately at startup, and then just before I start to really rev the engine up.

So what are the odds of an oil pump not pumping sufficient oil to my lifters?

 

[BogusSVO]

Also I did bleed all the lifters about 1k miles ago when I had the head hot tanked and resurfaced.

How much was milled from the head?

Lifter tic is the reason this mod came about, you may have oil flow to the head restricted.
http://www.dsmtuners.com/forums/newbie-forum/341028-4g63t-head-oil-port-mod.html

If the oil flow is too restricted, it will not matter how many times you change or bleed the HLAs, they will not recive the proper oil flow to find there home and lock into place.

So what are the odds of an oil pump not pumping sufficient oil to my lifters?

Doubt the pump is the issue.

Also with the increse in compression from 100-120 to 155-180 what did you do diffrent?

 

[bryanwheat]

A cracked exhaust manifold can sound an awful lot like a collapsed lifter.

 

[Aphix]

Also with the increse in compression from 100-120 to 155-180 what did you do diffrent?

Made a n00b mistake and kept the other 3 spark plugs in.

Also, I cant be certain how far the head was milled, it was done by a reputable guy in town my other dsm buddy has used on his 450 whp 1g, I actually had it go in for a hot tanking and have them redo the valve seals for 50 bucks. When I came to pick it up he told me he did a leak down test and ran a straight edge down it and said the head was too warped to hold a gasket, he told me a number and I read the spec on head warp and it was legitimately warped, but I forgot to ask him how much he took off unfortunately. Only charged me 80 bucks total too.

A cracked exhaust manifold can sound an awful lot like a collapsed lifter.

Thanks I will definitely take a look at the EM for cracks and check the bolts.

So would the fact it started tapping 2 or 3 weeks after the head was machined still be possible if the oil port was restricted? I am just wondering if I would notice it immediately or if it could take time for the lifters to bleed enough.