VerdeZ28

SO a little background: I have a 2002 Z06 that for a while has had a knocking noise right after a cold start that would subside and eventually stop as the car warmed up. I assumed this was a bad lifter at first till one day I start the car and it has NO OIL PRESSURE. I immediately shut it off and checked the oil level to make sure it wasent a hole in the oil pan or somthing. so that checked out and i started the car again and it built oil pressure but was at around 25psi instead of the normal 50psi or so.

so i preceded to let it sit for a while assuming i had to rebuild the engine and it has sat there for about 8 months now. yesterday i start it up to move it a bit, at this point im already convinced of a rebuild and doing a 383 stroker and all other things involved with that etc. and when it starts up it had NO OIL PRESSURE and was knocking a bit but then after a few seconds (maybe 20 seconds tops) it shoots up to 50psi as it would normally be and stayed there and the knock started to subside as before.

basically im asking can a bad lifter cause a low or no pressure reading. I have experienced this before with my brothers z28 and we ended up changing the lifters and oil pump and he hasent had an oil pressure issue since.
ill try to post a video of this when i can.

VerdeZ28

Any thoughts guys?

joecar

You answered your own question.

zzcamaro00

i second this. bum lifters can get noisy and if you also have a bum oil pump itll make it that much noisier. but i mean if your going into the engine why not just cam it, atleast some mild mods. and no LS7 lifters!!!

VerdeZ28

Yes but I am trying to gauge if people have experience the same issues. I know bad lifters can knock but can they affect oil pressure. Im trying to verify if what I experienced before with the Z28 was a fluke or if that really was the solution to the problem.

mainly I want to know has anyone else seen bad lifters affect oil pressure like as I described. because i know a spun bearing can cause the same issue.

RockinWs6

Very little, you wouldn't be losing 25 psi through the lifters unless one was broken in pieces. You might see lifters causing oil pressure gauge fluctuating a small amount. Moore likely you have oil pump -pickup tube problems.

Thing to consider is the oil pump pickup tube oring letting air past it. This will cause noisy lifters and lower than normal oil pressure.

joecar

Sounds like the pressure relief was hanging open and then it shut.

joecar

If a lifter was not present there would be a leak... if the lifter is present it restricts the leak (it regulates oil flow up the pushrods)... so a single lifter leaking (due to being internally stuck) may not cause that much drop in oil pressure, but maybe multiple lifters may.

joecar

If the o-ring were leaking air, it would not suddenly stop leaking air, it would be consistent.

RockinWs6

Depends the orings can move around and depending on temperature seal or leak. Mine leaks down cold but warmed up seals ok. Cold start I get terrible valve clatter everytime until the air purges out of the lifters. Hot its quiet as a mouse once the oring gets warmed up and seals. Its gotta be changed soon.

The oring wear over time and shrink, the acids in the engine oil also attack them. Its not always a tear failure but usually a wear failure.

RockinWs6

There is no place for the oil to leak inside the lifter except out the push rod bleed hole and its restricted. Like I said NOWAY you are losing 25 psi unless they are broken in pieces. Maybe a small fluctuation in the gauge if some were clogged and not bleeding oil up to rockers but that would actually make the pressure rise slightly.

joecar

Yeah, 25 psi does sound like too much.

VerdeZ28

So I have begun tearing into it. Took out one of the heads for now. I'll keep you guys posted. Will also be replacing heads and cam for a milled .030 243s and a .228/230 .571/.573 112 las cam. I don't think I should have any piston to valve clearance issues.