cylinder leakage test???

Doing a leakdown test on our SBC and we have a low leak (approximate 20%), I know that 20% isnt bad, sounds like the leak is past the valve seals, is this possible? Would replacing the seals change anything? I know it has to get past the valves to get to the seals but everything seems pretty tight? I can push down on the intake and cause it come out the carb and I can push down on the exhaust and make it come out there...
The compression tests and vacuum tests didnt pinpoint any problems but I have a miss and the thing smokes bad, like CARTOON bad...

any ideas?? thanks-

 

What color is the smoke? Does it stop after it warms up? Does it smoke at idle and on the road?

 

i have a couple of questions . if you have an engine miss have you done a cylinder balance test ? 2nd , is the reason for the leakdown to find said smoking concern ? 3rd , have you done a wet and dry compression test ? if so , what are the results of the balance and compression test . if it were me , that is where i would start at . also , what color is the smoke , and is it using a **** load of oil ?

 

With a cylinder properly at TDC, with both valves closed, the leak down will be past the rings or one of the valves. If the head gasket is bad, it can leak into another cylinder or into a water/oil port. I don't think it can leak past the valve stem seals...

 

IF you think you can hear the leak past the valve seals, my guess is you're actually hearing the sound from one of the oil return holes near the valve spring area, indicating the sound is in the crank case and coming from the rings leaking (or maybe the head gskt). Valve seals don't leak compression

 

as far as the cartoon smoke with only 20% leakdown, how about the intake gasket pulling oil from the lifter area, or a bad vacuum modulator if it's an auto trans?

 

I had that happen once. Found it by accident. I was going to rebuild/ lean out the carb, when I pulled the vacuum lines, red fluid. I was happy. $10 later it was fixed.

 

Good advice fro* Groucho. Valve seals only keep excess oil fro* going down the valve guides and don't do anything to seal co*pression in.

The valve guides would have to be beyond shot plus having bad valves to allow any air past the guides on a leakdown test and even then the air would go out the intake or out the exhaust first in 99.9999999 percent of the cases.

 

If you hear air coming from the valve area you have a gagged valve guide and the valve seat is leaking. Just keep the cylinder aired up and pull the springs off of that cylinder. Put a clamp on each valve stem and unhook the air hose. Do the wobble test on the valve and see what you have >>>>.