Leakdown Results - Bad Cylinder?

[wcover91]

Hey guys. I took my engine out this past winter for a good cleaning, some CIS refurb, and some rusty engine tin repair/repaint. I didn't want to do a full top end rebuild but did inspect all head studs and adjust all the valves into spec with the Stromski tool. I am in the final stages of reassembly with all my new looking parts. I decided to do a quick leadown test for the hell of it and came up with some upseting results.

I used a 100psi reference pressure. I went around the engine twice for double confirmation and here are the results.

1- 97, 97
6- 98, 99
2- 98, 97
4- 93, 95
3- 63, 64
5- 92, 94


As you can see cylinder 3 is way off from the rest which appear to be in pretty great shape. Listening to the test I don't hear much coming from the intake port. I hear a little coming from the exhaust port. I hear quite a bit coming from the breather outlet.

What do yall think? Could I have some busted rings on that piston? Is it bad? Do I need to take it all back apart to rebuild that cylinder?

[yelcab1]

Or, you may have just knocked some crud down the cylinder or have some deposit on the edge of the valves where they don't seal 100% anymore.

[Trakrat]

Originally Posted by wcover91

What do yall think? Could I have some busted rings on that piston? Is it bad? Do I need to take it all back apart to rebuild that cylinder?

I'd start with pulling the spark plug and taking a look at it. Clean the threads and reinstall it and run the test again.

Take the headers off and look up inside the exhaust port, have someone turn the engine and watch the valve open and close.

You could have anything from a stretched valve... crap getting caught in the valve clearance...

[wcover91]

I just pulled off the header on that side and turned the engine through it's cycle observing the valves move. Both intake and exhaust appear normal and seem to close. I tried blowing some air through to dislodge any potential debris. I don't know if this would actually do much though for a stuck particle. I then ran an endoscope down the spark plug hole to observe the piston top. Nothing seems out of the ordinary.

However, I am still getting roughly the same terrible leakdown on that cylinder. What has me worried is that it sounds like most of the air is coming through the breather outlet and not the valve seats. Enough that I can put my had in front of it and feel air.

[BK911]

Squirt some oil in the hole.
Rotate engine a few times.
Retest that hole.
If rings as you suspect, the results will improve.

[RedCoupe]

Originally Posted by BK911

Squirt some oil in the hole.
Rotate engine a few times.
Retest that hole.
If rings as you suspect, the results will improve.

+1 This is the definitive test for bad rings. The oil will temporarily seal the rings, so if this is the source of your compression loss, you will see a noticable improvement in the test.

[wcover91]

Hey everyone. I was finally able to do a wet leakdown test on the suspect cylinder. I turned the engine on its side and squirted a few pumps of oil down the spark plug hole then hooked up the tester. I got a reading of 82 (compared to 64).

So it seems the majority of the leakage is from the rings. This engine has about 120k with a rebuild about 20k ago. Could it really be bad/broken rings?

Is it possible I am just unlucky enough to have the rings currently aligned on that cylinder? Since the engine is on the stand I don't have the convenience to fire it up then test again later.

Any ideas on how I should proceed?

Are you confident in the head gasket on that cylinder?

[wcover91]

I would imagine if the head gasket was leaky there would be some grossness on the exterior of the cylinder and head. It looks very clean (cylinder 3).

[pmax]

Originally Posted by wcover91

So it seems the majority of the leakage is from the rings. This engine has about 120k with a rebuild about 20k ago. Could it really be bad/broken rings?

Maybe the ring never seated properly after.

[mikedsilva]

Sorry to hear about this.. sounds like it has to come apart again...

[Bill Douglas]

What does it look like in the exhaust port, compaired with the other cylinders. And what does the spark plug look like. Again does it look like the others.

[wcover91]

The spark plug, intake valve, and exhaust valve don't look any better or worse than any of the other cylinders.

Intake:


Exhaust:

[lateapex911]

So, the fact that u FEEL it coming out the breather is the indicator, IF you had a bad head gasket, you would't feel that AND you'd hear it running and see tell tale marks. I'd bet $$$ it's a issue with cylinder scoring (unlikely) or busted rings. Sorry.

While you're there, take a good look at everything.

Who built it? What ignition timing have you been running? Is the advance correct? You see where I'm going here, why did they break....and when??? Did you notice a drop in power??

[Bill Douglas]

I know less than everyone around here. But my take on it is... There is not a lot of black and not a lot of oil in the ports, which suggests that it's not a catastrophic failure, and I would be hesitant about tearing the engine down.

[Discseven]

WC... did you listen at intake/breather/exhaust when testing each cylinder? (This tells if there's valve---and what valve---or ring leak.)

[Mrdi]

Staying tuned to this post.

[Dan J]

You're 1 hr away from having that thing apart
It's always better to fix it before it fails
I've had a number of SC's over the years
with broken ring lands that would show those leakdown numbers
Just take it apart

[DRACO A5OG]

+1, do another test and this time try to find where it is leaking from or into case ( rings ) intake (valve), exhaust (valve), at the heads ( head at cylinder) or cylinder to case ( not likely but you never know )

I found mine was leaking out the head to cylinder matting area, as I clearly heard it coming out of my fan housing, it fretted the matting surface :-( horrible top end by POS

[Wayne 962]

What are the details on the "rebuild"? Was it simply a gasket refresh, or were new pistons and cylinders used? Re-ringed or same old used rings used? These are important details...

-Wayne