341am

I just recently built a d16z6. I broke the motor in pretty easy and had it tuned. It made good power, and had less then 2% leak down. At 2k miles after noticing that my catch can had a little oil in it, I decided to run another compression leak-down test. Cylinder 1,2, and 4 came out as 4% leak down, but cylinder #3 shows 65%. So with pressure still in the cylinder I pull my catch can line from the black box, and there is no pressure coming out. I pull the radiator cap off, and there are no bubbles. When the oil cap on the valve cover is removed, you can feel some slight pressure. I can only assume that it isn't the head gasket or rings. The thing that gets me is that the car runs the same as always, and doesn't smoke til high rpm, and full boost. Even then its only a small amount.

I'm stumped, and pretty sure the head will have to come off regardless. Any help on what this might be will be greatly appreciated.

Ok here's a little background on the setup.

Z6 block
vitaras and fj rods
acl duraglides
hastings rings
all oem gaskets (cometic HG)
oem water pump, oil pump, timing belt

Y8 head
supertech valvetrain
crower cam

Any help is greatly appreciated, Thank you in advance

341am

No one??

Fabrik8

I would guess that you have a ring sealing problem. The pressures that are used to do a leakdown test aren't high enough to make a ring seal dynamically in the same way that cylinder pressure would while the engine is running. So it may just be a case of that cylinder sealing properly while running but not sealing much at all during the leakdown test. That might explain the pressure at the valve cover and the oil in the catch can. Blowby past the rings will pressurize the crankcase and also pressurize the valve cover because they're connected. I can't really say for sure what the problem actually is, but that's my theory based on what you've said.

341am

Thanks for your reply...I did a normal compression test and the outcome was 180-180-120-180, cylinder 3 obviously being the lowest.

BAN HAMMER

my guess is maybe you forgot to stagger the rings on that piston?

Fabrik8

I've always thought that was a completely useless concept because the rings turn by themselves in normal engine operation.

BAN HAMMER

right, but by staggering them, there is a MUCH smaller chance of them all lining up at the same time. at least thats how its always been explained to me.

341am

The block was machined and assembled by apples machine shop. So I can't be certain, but that's what they do for a living so I can only assume.