# 2004 ls1 leak down test fail



## bluebluemblue (Dec 20, 2006)

Hey All,

I recently rebuilt the top end of my 2004 LS1. Springs, chain, pushrods, trunions, new cam etc.
This is prep for a twin turbo...plan 7 psi.

Engine ran fairly good (missing a bit) when I finally cranked it, Idle and 2000 rpm rev only. No boost.
It was rich from a previous tune and I assumed the miss was the tune.

So I lined up a dyno and a transport. The next day I went to turn the car around so it could be easily loaded on the transport.
Started missing badly, started smoking out the exhaust and popping loudly.
Then sputtered to a violent death. Attempts at restart, just pops out thye exhaust. Big problem.

So. Cancel dyno and transport.
Compression test. 211-207 on all 8. Only 30K miles. Thats OK.

Here is my query. I went to do a leakdown and all 8 seem they have no ability to hold compression. Air blows through at 100 PSI.
Rockers are off now but it never blew past either valves anyhow. 

Seems to be blowing into the pan...I know, bad rings or liner.

Just does not make since to me.
I have a true leak down tester on the way...though I do not think it will read any different.

My rig is a 200 PSI compressor with a male to female 100 psi gauge with a regulator. Spark plug hole hose (for in car spring change) Open that ragulator and it blows like nothing is there.

I took the RHS head off to have a look expecting a hole or something.
Even though I drained the radiator when I removed the head water ran onto the pistons. I quickly cleaned and blew that out. Point here is the pistons held water just fine. I know H2O thicker than O2 but...water sat there for a few minutes and did not go down at all. Took me a minute to gather cleaning stuff.

Air blows through like there is not a piston in all 8 cylinders.
My blow by did not seem excessive...but never was able to check once it died

Am I missing something, Hard to belive 8 rings failed in 20 minutes of rich running...but it seems that way.

Thoughts, Suggestions? I hate the implications. I just got this thing together.
Am I doing somethign stupid. I am about brain dead with this project.
Suggestion for the easiest cheapest fix...or smartest.

You have to know I just spent 2 months and a pile of money upgrading nearly every part of my 2004 GTO. 2 months of upgrades prior to this project.
Get it all together and...here I am. Not happy.
Thanks in advance
Blue


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## Phoenix (Dec 22, 2004)

Did you check piston to valve clearance? What are the specs on the new cam? A bent valve could cause what you are seeing. With the leakdown tester on, can you hear air coming out of the tail pipe, throttle body or PCV hose?


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## bluebluemblue (Dec 20, 2006)

Thanks for the reply

Yes, I checked all the usual suspect places you list. Valves are fine, pistons are fine.
I am still scratching my head.

I did the air test again and it seems to only blow out the valley. Valley plate is off. 
Does not seem to blow out the oil pan. I checked the drain hole. Engine oil empty.
Does not blow into the radiator.

I Have just now removed the LHS head. Engine is down to block and rotataing assembly again.All looks good on that side too.

Someone mentioned I could have a broken top ring.....all of them? 30K miles. Do a light test tomorrow. Have a new 2 bolt pick up tube thing anyhow. It came late.

I put 140 psi on each cylinder. Connected to the spark plug hole it slows the air a bit to 70 psi but flows like hell.

I am now thinking my Cometic head gaskets with ARP studs did not seal.
Hard to believe my heads or block are warped. I am building the top of this engine in the car. No machine work....yet.

No air came out around the head to block seal.
On a ls1 there is the lifter trays. I am thinking the air went through the MLS Cometic head gasket into the lifter tray opening.
This is my first use of MLS type gaskets. Did not use copper spray per Cometic.

Reality is I am stumped still. This is not my first engine.

The head gaskets look fine....as in they look new...not compressed. They are also coverd in a film of oil.

I torqued them in steps per ARP. Starting center middle and basically working towards the outside. Per GM 2004 GTO manual torque sequence. 80 lbs final per ARP.
I checked for what I thought maybe I did..tighten the bolts down on the shank of the stud. Its not that. Shank is shorter then the thickness of the head...just threads exposed

Pistons look fine. No play at all. No mark or score on the cylinder wall anywhere.

Besides the oil film and some arp thread seal the gaskets look NEW. Coating still on them. Raised areas still raised. I do not know, guess they rebound.


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