Hello all,

I finished putting together a rebuilt 06 4.8L ready for a good amount of boost. block and heads were sent to the machine shop for a full workup , BTR ls9 small bore headgaskets, ARP 2000 bolts, new pistons and rods, rings gapped to .026 top and .028 bottom.

My issue is that I found I had absolutley no compression in cylinder 7, I scoped that cylinder and didnt see any signs of scoring or piston damage, pulled the rockers and hooked a leak down test up to it and wouldn't hold any air.

I grabbed a hose and listened around and where Im certain it was coming from, it was around the head bolt in the center of the cylinder head.

I pulled the heads and did the liquid test on those valves and they are sealed, next i brought the piston to TDC and and back inspecting it closely. I didnt see any cylinder wall damage or piston damage.

Next i visually checked the headgasket and I cannot see any signs of blowby.

I am here now because I am stumped and nlt aure my next step, other than trying a new headgasket.

I hope I supplied enough information so that someone can guide me in the right direction.

I can attach pictures later today if neccessary.

Cheers

 

Welcome to the forum!

The head bolt was where it was leaking from? That's strange. What casting are the heads? I believe a handful had issues with cracking, but I thought that caused some coolant to burn off?

Was the block decked? You verified all head bolts were torqued down? It's not difficult to actually miss tightening a bolt, with some many bolts.

 

Hello, the air sounded like it was coming from around the headbolt area, I can attach a picture with the area circled.

Ive inspected the heads and havent seem any cracking, also the block leaks like new. I did have the block decked, honed and the heads resurfaced.

My cooling system was normal and wasnt burning any coolant or being pressurized. since I was seeing around 14psi of boost i would of found out real quick if it was bad.

I am confident I torqued them all down to with the required ARP instructions.

I will attach a picture of the bank of cylinders aa well and when I get home I can get pictures of the head gasket.

It will be the far right cylinder and piston area.

 

And then you post pictures of an engine with many hours of run time. There is a big part of the story missing. You put in new pistons and rings and found no compression in #7.
You then posted,

Quote:

Originally Posted by Rustysleeper

...since I was seeing around 14psi of boost i would of found out real quick if it was bad...

The engine in the pictures ran quite a while before you took the pictures that you posted. So what happened to make you test the compression, and why did you think it was not important to tell us?

 

My apologies for missing that part, I rebuilt it a couple weeks ago and have driven it around a 1000 miles. it hasn't shown any misfires on my data logging software and with the aggressive camshaft I couldn't tell that it was running rough. No smoke out of my catch can, my only concern was the lack of power it was making.

So first I pulled injectors and it didnt change the idle, checked for spark and it had spark, next was compression testing all cylinders and 7 cylinder were all within 3 to 5 psi of each other. The 8th cylinder being 0 psi.

So I tried a leak down test and it wouldn't hold at all, checked cylinder with a bore scope and didnt see any signs of damage .

I pulled valve covers and removed rockers and tried leak down again and same thing, it would hold no air. so i cranked the air in and listens around with a hose and tried to pin point where the air was leaking.

There hasnt been any knock or misfires, havent leaned it. I pulled the head and haven't been able to find it. I am going to pull apart the 7 layer head gasket to see if there is any signs between the layers.

I get i didnt give the full or exact details but all im asking is for some guidance to help me figure this out.

If I am missing anything i will gladly supply information so i can get my truck back together without throwing parts at it.

Cheers

 

The far right cylinder in the picture shows that it had enough compression to combust the mixture at some time, or during certain conditions, during those 1000 miles, not sure if that means anything.
I don't think that the head gasket would be the culprit, but I am sorry that I can't be more helpful than that.

 

I would guess that you were hearing leakage in the crankcase through that bolt access hole, but it makes no sense (obviously) as to why it's centered around only one hole.

 

Thank you for the response, I apologize again for any lack of information. I will continue to figure it out and keep using Google to help track down the issue.

I will also say that when I pulled the cylinder head and what coolant I had left in the cylinder head/block drained out and went into the cylinders i noticed it didnt just drain away. My theory is the rings seem to be still intact.

Also the spark plug looked normal like all the others.

my plan is to try a new head gasket and use my old factory bolts and attempt a leak down test again 😅. Then if all is well ill switch them out to my ARP bolts. Im hoping I dont have to drop the pan or pull the motor again. If I dont succeed I will be dropping the oil pan again.


Cheers

 

Thats only 1000 miles of run time and the pistons look like that?
Never seen one with so much carbon build up in such a short amount of time.

That #7 piston is solid black while the others are showing only partially covered.
#5 is mighty clean looking.

Did you try and pressurize #5?
Sometimes you will hear air going past the rings and where the head bolt is, there is a passage to the crank case by the lifters so i bet thats what you were hearing.

Your this far into it, just pull #7 piston out and see what it looks like. could be a broken ring land.

 

I couldnt tell you why the pistons have that much build up, I have only been learning this stuff for about 2 years now.

I didnt check the leak down in cylinder 5, the compression was the same as the rest so i didnt think to check that one.

I hate to hear that I should pull it but you are probably right.